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Primary familial brain calcification (PFBC) is a genetic neurological disease, yet no effective treatment is currently available. Here, we identified five novel intronic variants in SLC20A2 gene from six PFBC families. Three of these variants increased aberrant SLC20A2 pre-mRNA splicing by altering the binding affinity of splicing machineries to newly characterized cryptic exons, ultimately causing premature termination of SLC20A2 translation. Inhibiting the cryptic-exon incorporation with splice-switching ASOs increased the expression levels of functional SLC20A2 in cells carrying SLC20A2 mutations. Moreover, by knocking in a humanized SLC20A2 intron 2 sequence carrying a PFBC-associated intronic variant, the SLC20A2 -KI mice exhibited increased inorganic phosphate (Pi) levels in cerebrospinal fluid (CSF) and progressive brain calcification. Intracerebroventricular administration of ASOs to these SLC20A2 -KI mice reduced CSF Pi levels and suppressed brain calcification. Together, our findings expand the genetic etiology of PFBC and demonstrate ASO-mediated splice modulation as a potential therapy for PFBC patients with SLC20A2 haploinsufficiency. [Display omitted] • Cryptic-exon incorporation reduces SLC20A2 mRNA expression • Splice-switching ASOs restore SLC20A2 expression in patient-derived cells • Humanized SLC20A2 knockin mice phenocopy PFBC pathology • ASOs restore brain phosphate homeostasis and suppress brain calcification Zhao et al. discover that mRNA and protein expression of phosphate importer SLC20A2 is compromised by intronic mutations, which resulted in increased cryptic-exon incorporation. Splice-switching ASOs targeting cryptic exons restore SLC20A2 expression and brain phosphate homeostasis and suppress brain calcification, providing a therapeutic strategy for PFBC patients with SLC20A2 haploinsufficiency. [ABSTRACT FROM AUTHOR]

该文报道1例特发性基底节钙化病例, 临床主要表现为进行加重性运动障碍, 头颅 CT 扫描提 示双侧基底节、丘脑、小脑、大脑半球广泛性对称性钙化病灶, 二代基因测序示 SLC20A2基因突变. 特发性基 底节钙化是一种罕见的对称性基底节或其他部位钙化的遗传性神经疾病, 临床表现多样, 越来越多的致病基因 被认识, 不同致病基因临床特征不一. 此病例同一家族谱系2位家属与患者钙化灶类似而临床症状表现各不 相同. 分析其临床特点、病程演变过程及影像学特点, 以提高临床医师对罕见病的诊断. [ABSTRACT FROM AUTHOR]

Abstract Background Idiopathic basal ganglia calcification (IBGC) is a genetic disorder of the nervous system commonly known as Fahr disease. IBGC patients with a genetic background are considered to have primary familial brain calcification (PFBC), also known as familial basal ganglia calcification (FBGC), or familial Fahr disease. It is a rare degenerative neurological disorder characterized by extensive bilateral basal ganglia calcification that can lead to a range of extrapyramidal symptoms and neuropsychiatric manifestations. Studies have suggested that more than 50 variants of SLC20A2 gene mutations account for approximately 50% of IBGC cases. There is a wide spectrum of mutation types, including frameshift, nonsense, and splice site mutations in addition to deletion and missense mutations. Here we report a case of familial basal ganglia calcification caused by a frameshift mutation in the SLC20A2 gene. We identified a heterozygous mutation in the SLC20A2 gene, c.1097delG (p.G366fs*89). To our knowledge, this mutation site has not been reported before. Case presentation A 57-year-old male patient was admitted to the hospital with “unstable walking and involuntary movements between the eyes and eyebrows for 6 months”. Based on the patient’s family history, symmetrical calcification foci in the bilateral caudate nucleus head, thalamus, cerebellum and parietal lobe indicated by head CT, and gene test results, the diagnosis of familial Fahr disease caused by mutations in the SLC20A2 gene, c.1097delG p.G366fs*89) was confirmed. Conclusion For the first time, we identified c.1097delG (p.G366fs*89) as a frameshift mutation in the IBGC family. This frameshift mutation caused the condition in this family of patients. This mutation not only broadens the range of known SLC20A2 mutations but also aids in the genetic diagnosis of IBGC.

Many conditions can present with accumulation of calcium in the brain and manifest with a variety of neurological symptoms. Brain calcifications can be primary (idiopathic or genetic) or secondary to various pathological conditions (e.g., calcium–phosphate metabolism derangement, autoimmune disorders and infections, among others). A set of causative genes associated with primary familial brain calcification (PFBC) has now been identified, and include genes such as SLC20A2, PDGFB, PDGFRB, XPR1, MYORG, and JAM2. However, many more genes are known to be linked with complex syndromes characterized by brain calcifications and additional neurologic and systemic manifestations. Of note, many of these genes encode for proteins involved in cerebrovascular and blood–brain barrier functions, which both represent key anatomical structures related to these pathological phenomena. As a growing number of genes associated with brain calcifications is identified, pathways involved in these conditions are beginning to be understood. Our comprehensive review of the genetic, molecular, and clinical aspects of brain calcifications offers a framework for clinicians and researchers in the field. [ABSTRACT FROM AUTHOR]

The Golgi apparatus is vital for protein modification and molecular trafficking. It is essential for nerve development and activity, and damage thereof is implicated in many neurological diseases. Primary familial brain calcification (PFBC) is a rare inherited neurodegenerative disease characterized by multiple brain calcifications. SLC20A2 , which encodes the inorganic phosphate transporter 2 (PiT-2) protein, is the main pathogenic gene in PFBC. The PiT-2 protein is a sodium-dependent phosphate type III transporter, and dysfunction leads to a deficit in the cellular intake of inorganic phosphate (Pi) and calcium deposits. Whether the impaired Golgi apparatus is involved in the PFBC procession requires elucidation. In this study, we constructed induced pluripotent stem cells (iPSCs) derived from two PFBC patients with different SLC20A2 gene mutations (c.613G > A or del exon10) and two healthy volunteers as dependable cell models for research on pathogenic mechanism. To study the mechanism, we differentiated iPSCs into neurons and astrocytes in vitro. Our study found disruptive Golgi structure and damaged autophagy in PFBC neurons with increased activity of mTOR. We also found damaged mitochondria and increased apoptosis in the PFBC dopaminergic neurons and astrocytes. In this study, we prove that dysfunctional PiT-2 leads to an imbalance of cellular Pi, which may disrupt the Golgi apparatus with impaired autophagy, mitochondria and apoptosis in PFBC. Our study provides a new avenue for understanding nerve damage and pathogenic mechanism in brain calcifications. [Display omitted] • Neurons and astrocytes differentiated from PFBC-patient-derived iPSCs have same gene mutation and symptoms with the donors. • Dysfunctional PiT-2 caused to Golgi disruption in PFBC. • Impaired autophagy and mitochondria also participated in PFBC. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC) is a rare neurodegenerative and neuropsychiatric disorder characterized by bilateral symmetric intracranial calcification along the microvessels or inside neuronal cells in the basal ganglia, thalamus, and cerebellum. Slc20a2 homozygous (HO) knockout mice are the most commonly used model to simulate the brain calcification phenotype observed in human patients. However, the cellular and molecular mechanisms related to brain calcification, particularly at the early stage much prior to the emergence of brain calcification, remain largely unknown. In this study, we quantified the central nervous system (CNS)-infiltrating T-cells of different age groups of Slc20a2-HO and matched wild type mice and found CD45+ CD3+ T-cells to be significantly increased in the brain parenchyma, even in the pre-calcification stage of 1-month-old -HO mice. The accumulation of the CD3+ T-cells appeared to be associated with the severity of brain calcification. Further immunophenotyping revealed that the two main subtypes that had increased in the brain were CD3+ CD4- CD8- and CD3+ CD4+ T-cells. The expression of endothelial cell (EC) adhesion molecules increased, while that of tight and adherents junction proteins decreased, providing the molecular precondition for T-cell recruitment to ECs and paracellular migration into the brain. The fusion of lymphocytes and EC membranes and transcellular migration of CD3-related gold particles were captured, suggesting enhancement of transcytosis in the brain ECs. Exogenous fluorescent tracers and endogenous IgG and albumin leakage also revealed an impairment of transcellular pathway in the ECs. FTY720 significantly alleviated brain calcification, probably by reducing T-cell infiltration, modulating neuroinflammation and ossification process, and enhancing the autophagy and phagocytosis of CNS-resident immune cells. This study clearly demonstrated CNS-infiltrating T-cells to be associated with the progression of brain calcification. Impairment of blood–brain barrier (BBB) permeability, which was closely related to T-cell invasion into the CNS, could be explained by the BBB alterations of an increase in the paracellular and transcellular pathways of brain ECs. FTY720 was found to be a potential drug to protect patients from PFBC-related lesions in the future. [ABSTRACT FROM AUTHOR]

Primary brain calcification (PBC), also known as idiopathic basal ganglia calcification (IBGC), primary familial brain calcification (PFBC) and so on, is a rare intractable disease characterized by abnormal mineral deposits, including mostly calcium in the basal ganglia, thalamus, and cerebellum. The causative gene of familial PBC is SLC20A2 , which encodes the phosphate transporter PiT-2. Despite this knowledge, the molecular mechanism underlying SLC20A2 -associated PBC remains unclear. In the present study, we investigated whether haploinsufficiency or a dominant-negative mechanism reduced Pi uptake in two PiT-2 variants (T115 M and R467X). We demonstrated that the presence of T115 M or R467X had no dominant-negative effect on Pi transport activity of wild-type (WT). In addition, the subcellular localization of R467X completely differed from that of WT, indicating that there is no interaction between R467X and WT. Conversely, T115 M and WT showed almost the same localization. Therefore, we examined the interaction between T115 M and WT using the bioluminescence resonance energy transfer (BRET) method. Although WT and T115 M interact with each other, T115 M does not inhibit WT's Pi transport activity. These results suggest that the role of SLC20A2 in the pathogenesis of PBC may involve decreased intracellular Pi uptake by a haploinsufficiency mechanism rather than a dominant-negative mechanism; agents promoting PiT-2 dimerization may be promising potential therapeutic agents for PBC. • The SLC20A2 gene was first identified as a causative gene of PBC. • The role of SLC20A2 in PBC may involve decreased Pi uptake by a haploinsufficiency mechanism. • Agents promoting PiT-2 may be promising potential therapeutic agents for PBC. [ABSTRACT FROM AUTHOR]

Aberrant inorganic phosphate (Pi) homeostasis causes brain calcification and aggravates neurodegeneration, but the underlying mechanism remains unclear. Here, we found that primary familial brain calcification (PFBC)-associated Pi transporter genes Pit2 and Xpr1 were highly expressed in astrocytes, with importer PiT2 distributed over the entire astrocyte processes and exporter XPR1 localized to astrocyte end-feet on blood vessels. This polarized PiT2 and XPR1 distribution endowed astrocyte with Pi transport capacity competent for brain Pi homeostasis, which was disrupted in mice with astrocyte-specific knockout (KO) of either Pit2 or Xpr1. Moreover, we found that Pi uptake by PiT2, and its facilitation by PFBC-associated galactosidase MYORG, were required for the high Pi transport capacity of astrocytes. Finally, brain calcification was suppressed by astrocyte-specific PiT2 re-expression in Pit2 -KO mice. Thus, astrocyte-mediated Pi transport is pivotal for brain Pi homeostasis, and elevating astrocytic Pi transporter function represents a potential therapeutic strategy for reducing brain calcification. [Display omitted] • Enriched and polarized distribution of PiT2 and XPR1 in astrocytes • Astrocyte-mediated Pi transport is essential for brain Pi homeostasis • MYORG facilitates PiT2 membrane expression and transporter function in astrocytes • Therapeutical re-expression of PiT2 in astrocytes suppresses brain calcification Cheng et al. discover that astrocytes transport inorganic phosphate through the polarized distribution of importer PiT2 and exporter XPR1, which maintain brain homeostasis of inorganic phosphate, providing a therapeutic strategy for calcification amelioration in patients with primary basal ganglion calcification. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC), often called Fahr's disease, is a condition in which calcium phosphate accumulates in the brain, mainly in the basal ganglia, thalamus, and cerebellum, and without the association of any metabolic or infectious cause. Patients present a variety of neurological and psychiatric disorders, usually during adulthood. The disease is caused by autosomal dominant pathogenic variants in genes such as SLC20A2, PDGFRB, PDGFB, and XPR1. MYORG and JAM2 are the other genes linked to homozygous patterns of inheritance. Here, we briefly discuss the recent cases reported by Ceylan et al. (2022) and Al-Kasbi et al. (2022), which challenge the current association with two previous genes and a clear pattern of inheritance. Ceylan et al. report a new biallelic variant related to a pathogenic variant in the SLC20A2 gene, which is typically associated with a heterozygous mutation pattern. The affected siblings displayed a severe and early onset of the disease, revealing a phenotype similar to that seen in CMV infections, often named as pseudo-TORCH. Furthermore, a study of genes related to intellectual disability conducted by Al-Kasbi et al. demonstrated that the biallelic manifestation of the XPR1 gene was associated with early symptoms, leading to the belief that the homozygous pattern of genes responsible for causing PFBC with an autosomal dominant pattern may also be linked to early-onset manifestations of PFBC. Further studies might explore the variety of clinical presentations linked to PFBC genes, especially if we pay attention to complex patterns of inheritance, reinforcing the need for a more detailed bioinformatic analysis. [ABSTRACT FROM AUTHOR]

Tics, Tourettism, primary familial brain calcification, SLC20A2 Keywords: tics; Tourettism; primary familial brain calcification; SLC20A2 EN tics Tourettism primary familial brain calcification SLC20A2 1152 1154 3 07/21/23 20230701 NES 230701 Primary Familial Brain Calcification (PFBC) is a genetic disorder characterized by bilateral abnormal calcium deposition in one or more regions of the brain in the absence of a secondary cause.[1] Its genotypic and phenotypic spectrum continues to evolve and be elucidated.[2] Here, we describe a patient with PFBC due to a pathogenic variant in the solute carrier family 20 member 2 ( I SLC20A2) i gene who presented with adult-onset Tourettism. Imaging in the patient demonstrated bilateral basal ganglia, posterior thalami, and frontal and parietal subcortical white matter calcifications (Fig. [Extracted from the article]

Background: Idiopathic basal ganglia calcification (IBGC) is a genetic disorder of the nervous system commonly known as Fahr disease. IBGC patients with a genetic background are considered to have primary familial brain calcification (PFBC), also known as familial basal ganglia calcification (FBGC), or familial Fahr disease. It is a rare degenerative neurological disorder characterized by extensive bilateral basal ganglia calcification that can lead to a range of extrapyramidal symptoms and neuropsychiatric manifestations. Studies have suggested that more than 50 variants of SLC20A2 gene mutations account for approximately 50% of IBGC cases. There is a wide spectrum of mutation types, including frameshift, nonsense, and splice site mutations in addition to deletion and missense mutations. Here we report a case of familial basal ganglia calcification caused by a frameshift mutation in the SLC20A2 gene. We identified a heterozygous mutation in the SLC20A2 gene, c.1097delG (p.G366fs*89). To our knowledge, this mutation site has not been reported before.Case Presentation: A 57-year-old male patient was admitted to the hospital with "unstable walking and involuntary movements between the eyes and eyebrows for 6 months". Based on the patient's family history, symmetrical calcification foci in the bilateral caudate nucleus head, thalamus, cerebellum and parietal lobe indicated by head CT, and gene test results, the diagnosis of familial Fahr disease caused by mutations in the SLC20A2 gene, c.1097delG p.G366fs*89) was confirmed.Conclusion: For the first time, we identified c.1097delG (p.G366fs*89) as a frameshift mutation in the IBGC family. This frameshift mutation caused the condition in this family of patients. This mutation not only broadens the range of known SLC20A2 mutations but also aids in the genetic diagnosis of IBGC. [ABSTRACT FROM AUTHOR]

Keywords: gaze palsy; parkinsonism; PFBC; SLC20A2 EN gaze palsy parkinsonism PFBC SLC20A2 501 503 3 03/23/23 20230301 NES 230301 The spectrum of clinical features associated with Primary Familial Brain Calcification (PFBC) remains broad. An axial cut centered in the midbrain does not reveal any calcification. gl To date, VSGP has been reported in only eight patients with diffuse brain calcification, four diagnosed with PFBC. [Extracted from the article]

Many conditions can present with accumulation of calcium in the brain and manifest with a variety of neurological symptoms. Brain calcifications can be primary (idiopathic or genetic) or secondary to various pathological conditions (e.g., calcium–phosphate metabolism derangement, autoimmune disorders and infections, among others). A set of causative genes associated with primary familial brain calcification (PFBC) has now been identified, and include genes such as SLC20A2, PDGFB, PDGFRB, XPR1, MYORG, and JAM2. However, many more genes are known to be linked with complex syndromes characterized by brain calcifications and additional neurologic and systemic manifestations. Of note, many of these genes encode for proteins involved in cerebrovascular and blood–brain barrier functions, which both represent key anatomical structures related to these pathological phenomena. As a growing number of genes associated with brain calcifications is identified, pathways involved in these conditions are beginning to be understood. Our comprehensive review of the genetic, molecular, and clinical aspects of brain calcifications offers a framework for clinicians and researchers in the field.

We describe a postmortem case of familial idiopathic basal ganglia calcification (FIBGC) in a 72‐year‐old Japanese man. The patient showed progressive cognitive impairment with a seven‐year clinical course and calcification of the basal ganglia, thalami, and cerebellar dentate nuclei. A novel heterozygous missense variant in SLC20A2 (c.920C>T/p.P307L), a type III sodium‐dependent phosphate transporter (PiT‐2), was subsequently identified, in addition to typical neuropathological findings of FIBGC, such as capillary calcification of the occipital gray matter, confluent calcification of the basal ganglia and cerebellar white matter, widespread occurrence of vasculopathic changes, cerebrovascular lesions, and vascular smooth muscle cell depletion. Immunohistochemistry for PiT‐2 protein revealed no apparent staining in endothelial cells in the basal ganglia and insular cortex; however, the immunoreactivity in endothelial cells of the cerebellum was preserved. Moreover, Western blot analysis identified preserved PiT‐2 immunoreactivity signals in the frontal cortex and cerebellum. The variant identified in the present patient could be associated with development of FIBGC and is known to be located at the large intracytoplasmic part of the PiT‐2 protein, which has potential phosphorylation sites with importance in the regulation of inorganic phosphate transport activity. The present case is an important example to prove that FIGBC could stem from a missense variant in the large intracytoplasmic loop of the PiT‐2 protein. Abnormal clearance of inorganic phosphate in the brain could be related to the development of vascular smooth muscle damage, the formation of cerebrovascular lesions, and subsequent brain calcification in patients with FIBGC with SLC20A2 variants. [ABSTRACT FROM AUTHOR]

This systematic MDSGene review covers individuals with confirmed genetic forms of primary familial brain calcification (PFBC) available in the literature. Data on 516 (47% men) individuals, carrying heterozygous variants in SLC20A2 (solute carrier family 20 member 2, 61%), PDGFB (platelet‐derived growth factor subunit B, 12%), XPR1 (xenotropic and polytropic retrovirus receptor, 16%), or PDGFRB (platelet‐derived growth factor receptor beta, 5%) or biallelic variants in MYORG (myogenesis‐regulating glycosidase, 13%) or JAM2 (junctional adhesion molecule 2, 2%), were extracted from 93 articles. Nearly one‐third of the mutation carriers were clinically unaffected. Carriers of PDGFRB variants were more likely to be clinically unaffected (~54%), and the penetrance of SLC20A2 and XPR1 variants (<70%) was lower in comparison to the remaining three genes (>85%). Among the 349 clinically affected patients, 27% showed only motor and 31% only nonmotor symptoms/signs, whereas the remaining 42% had a combination thereof. While parkinsonism and speech disturbance were the most frequently reported motor manifestations, cognitive deficits, headache, and depression were the major nonmotor symptoms/signs. The basal ganglia were always calcified, and the cerebellum, thalamus, and white matter contained calcifications in 58%, 53%, and 43%, respectively, of individuals. In autosomal‐dominant PFBC, mutation severity influenced the number of calcified brain areas, which in turn correlated with the clinical status, whereby the risk of developing symptoms/signs more than doubled for each additional region with calcifications. Our systematic analysis provides the most comprehensive insight into genetic, clinical, and neuroimaging features of known PFBC forms, to date. In addition, it puts forth the penetrance estimates and newly discovered genotype–phenotype relations that will improve counseling of individuals with mutations in PFBC genes. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society [ABSTRACT FROM AUTHOR]

The suprachiasmatic nucleus (SCN) encodes time of day through changes in daily firing; however, the molecular mechanisms by which the SCN times behavior are not fully understood. To identify factors that could encode day/night differences in activity, we combine patch-clamp recordings and single-cell sequencing of individual SCN neurons in mice. We identify PiT2 , a phosphate transporter, as being upregulated in a population of Vip + Nms + SCN neurons at night. Although nocturnal and typically showing a peak of activity at lights off, mice lacking PiT2 (PiT2 −/−) do not reach the activity level seen in wild-type mice during the light/dark transition. PiT2 loss leads to increased SCN neuronal firing and broad changes in SCN protein phosphorylation. PiT2 −/− mice display a deficit in seasonal entrainment when moving from a simulated short summer to longer winter nights. This suggests that PiT2 is responsible for timing activity and is a driver of SCN plasticity allowing seasonal entrainment. [Display omitted] • PiT2 expression is upregulated in night-active Vip + Nms + SCN neurons • Mice lacking PiT2 show decreased behavioral activity at the light/dark transition • Loss of PiT2 leads to increased SCN neuronal firing and phosphorylation changes in the SCN • Winter seasonality entrainment depends on PiT2 function in SCN neurons Pierre-Ferrer et al. report that the phosphate transporter PiT2 regulates behavior at the light/dark transition in mice by decreasing the firing frequency and modifying the phosphorylation landscape of suprachiasmatic nucleus (SCN) neurons. Furthermore, PiT2 is essential for proper winter seasonality entrainment at the light/dark transition. [ABSTRACT FROM AUTHOR]

Brain calcifications are frequent findings on imaging. In a small proportion of cases, these calcifications are associated with pathogenic gene variants, hence termed primary familial brain calcification (PFBC). The clinical penetrance is incomplete and phenotypic variability is substantial. This paper aims to characterize a Swedish PFBC cohort including 25 patients: 20 from seven families and five sporadic cases. Longitudinal clinical assessment and CT imaging were conducted, abnormalities were assessed using the total calcification score (TCS). Genetic analyses, including a panel of six known PFBC genes, were performed in all index and sporadic cases. Additionally, three patients carrying a novel pathogenic copy number variant in SLC20A2 had their cerebrospinal fluid phosphate (CSF-Pi) levels measured. Among the 25 patients, the majority (76%) displayed varying symptoms during the initial assessment including motor (60%), psychiatric (40%), and/or cognitive abnormalities (24%). Clinical progression was observed in most patients (78.6%), but there was no significant difference in calcification between the first and second scans, with mean scores of 27.3 and 32.8, respectively. In three families and two sporadic cases, pathogenic genetic variants were identified, including a novel finding, in the SLC20A2 gene. In the three tested patients, the CSF-Pi levels were normal. This report demonstrates the variable expressivity seen in PFBC and includes a novel pathogenic variant in the SLC20A2 gene. In four families and three sporadic cases, no pathogenic variants were found, suggesting that new PFBC genes remain to be discovered. • Brain calcification was variable, predominantly seen in central structures. • Most patients (76%) exhibited motor, psychiatric, and/or cognitive symptoms. • There was clinical progression in most but only a modest increase in calcification. • We identified a novel pathogenic genetic variant in the SLC20A2 gene. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC, OMIM#213600), also known as Fahr's disease, is characterized by bilateral and symmetric brain calcification in the basal ganglia (globus pallidus, caudate nucleus, and putamen), thalamus, subcortical white matter, and cerebellum. PFBC can be caused by loss-of-function mutations in any of the six known causative genes. The most common clinical manifestations include movement disorders, cognitive impairment, and neuropsychiatric signs that gradually emerge in middle-aged patients. To broaden the PFBC mutation spectrum, we examined nine members of a family with PFBC and two sporadic cases from clinical departments, and sequenced all PFBC-causative genes in the index case. Two novel frameshift mutations in SLC20A2 [NM_001257180.2; c.806delC, p.(Pro269Glnfs*49) and c.1154delG, p.(Ser385Ilefs*70)] and one novel splice donor site mutation (NM_002608.4, c.456+1G>C, r.436_456del) in PDGFB were identified in the patient cohort. c.806delC co-segregated with brain calcification and led to SLC20A2 haploinsufficiency among the affected family members. The c.456+1G>C mutation in PDGFB resulted in aberrant mRNA splicing, thereby forming mature transcripts containing an in-frame 21 base pair (bp) deletion, which might create a stably truncated protein [p.(Val146_Gln152del)] and exert a dominant negative effect on wild-type PDGFB. All three mutations were located in highly conserved regions among multiple species and predicted to be pathogenic, as evaluated by at least eight common genetic variation scoring systems. This study identified three novel mutations in SLC20A2 and PDGFB, which broadened and enriched the PFBC mutation spectrum.

Abstract Background Primary familial brain calcification (PFBC) is a rare inheritable neurodegenerative disease characterized by bilateral calcification in different brain regions and by a range of neuropsychiatric symptoms. Six causative genes of PFBC (SLC20A2, PDGFRB, PDGFB, XPR1, MYORG, and JAM2) have been identified. Methods Sanger sequencing was used to identify the causative genes associated with PFBC in this study. Results We describe the first PFBC case with both SLC20A2 and PDGFRB heterozygous mutations. Notably, this patient with the digenic mutation (who was only 5 years old) showed severe brain calcification and migraine, whereas the patient's parents, who each carried a heterozygous mutation in SLC20A2 or PDGFRB, exhibited varying degrees of brain calcification but were clinically asymptomatic. Conclusion This case highlights the digenic influences on the characteristics of PFBC patients.

BackgroundPrimary familial brain calcification (PFBC, OMIM#213600), also known as Fahr’s disease, is a rare autosomal dominant or recessive neurodegenerative disorder characterized by bilateral and symmetrical microvascular calcifications affecting multiple brain regions, particularly the basal ganglia (globus pallidus, caudate nucleus, and putamen) and thalamus. The most common clinical manifestations include cognitive impairment, neuropsychiatric signs, and movement disorders. Loss-of-function mutations in SLC20A2 are the major genetic causes of PFBC.ObjectiveThis study aimed to investigate whether Slc20a2 knockout mice could recapitulate the dynamic processes and patterns of brain calcification and neurological symptoms in patients with PFBC. We comprehensively evaluated brain calcifications and PFBC-related behavioral abnormalities in Slc20a2-deficient mice.MethodsBrain calcifications were analyzed using classic calcium-phosphate staining methods. The Morris water maze, Y-maze, and fear conditioning paradigms were used to evaluate long-term spatial learning memory, working memory, and episodic memory, respectively. Sensorimotor gating was mainly assessed using the prepulse inhibition of the startle reflex program. Spontaneous locomotor activity and motor coordination abilities were evaluated using the spontaneous activity chamber, cylinder test, accelerating rotor-rod, and narrowing balance beam tests.ResultsSlc20a2 homozygous knockout (Slc20a2-HO) mice showed congenital and global developmental delay, lean body mass, skeletal malformation, and a high proportion of unilateral or bilateral eye defects. Brain calcifications were detected in the hypothalamus, ventral thalamus, and midbrain early at postnatal day 80 in Slc20a2-HO mice, but were seldom found in Slc20a2 heterozygous knockout (Slc20a2-HE) mice, even at extremely old age. Slc20a2-HO mice exhibited spatial learning memory impairments and sensorimotor gating deficits while exhibiting normal working and episodic memories. The general locomotor activity, motor balance, and coordination abilities were not statistically different between Slc20a2-HO and wild-type mice after adjusting for body weight, which was a major confounding factor in our motor function evaluations.ConclusionThe human PFBC-related phenotypes were highly similar to those in Slc20a2-HO mice. Therefore, Slc20a2-HO mice might be suitable for the future evaluation of neuropharmacological intervention strategies targeting cognitive and neuropsychiatric impairments.

Primary familial brain calcification (PFBC, OMIM#213600), also known as Fahr's disease, is characterized by bilateral and symmetric brain calcification in the basal ganglia (globus pallidus, caudate nucleus, and putamen), thalamus, subcortical white matter, and cerebellum. PFBC can be caused by loss-of-function mutations in any of the six known causative genes. The most common clinical manifestations include movement disorders, cognitive impairment, and neuropsychiatric signs that gradually emerge in middle-aged patients. To broaden the PFBC mutation spectrum, we examined nine members of a family with PFBC and two sporadic cases from clinical departments, and sequenced all PFBC-causative genes in the index case. Two novel frameshift mutations in SLC20A2 [NM_001257180.2; c.806delC, p.(Pro269Glnfs*49) and c.1154delG, p.(Ser385Ilefs*70)] and one novel splice donor site mutation (NM_002608.4, c.456+1G>C, r.436_456del) in PDGFB were identified in the patient cohort. c.806delC co-segregated with brain calcification and led to SLC20A2 haploinsufficiency among the affected family members. The c.456+1G>C mutation in PDGFB resulted in aberrant mRNA splicing, thereby forming mature transcripts containing an in-frame 21 base pair (bp) deletion, which might create a stably truncated protein [p.(Val146_Gln152del)] and exert a dominant negative effect on wild-type PDGFB. All three mutations were located in highly conserved regions among multiple species and predicted to be pathogenic, as evaluated by at least eight common genetic variation scoring systems. This study identified three novel mutations in SLC20A2 and PDGFB , which broadened and enriched the PFBC mutation spectrum. [ABSTRACT FROM AUTHOR]

Background: Primary familial brain calcification (PFBC) is a rare inheritable neurodegenerative disease characterized by bilateral calcification in different brain regions and by a range of neuropsychiatric symptoms. Six causative genes of PFBC (SLC20A2, PDGFRB, PDGFB, XPR1, MYORG, and JAM2) have been identified. Methods: Sanger sequencing was used to identify the causative genes associated with PFBC in this study. Results: We describe the first PFBC case with both SLC20A2 and PDGFRB heterozygous mutations. Notably, this patient with the digenic mutation (who was only 5 years old) showed severe brain calcification and migraine, whereas the patient's parents, who each carried a heterozygous mutation in SLC20A2 or PDGFRB, exhibited varying degrees of brain calcification but were clinically asymptomatic. Conclusion: This case highlights the digenic influences on the characteristics of PFBC patients. [ABSTRACT FROM AUTHOR]

Background: Primary familial brain calcification (PFBC, OMIM#213600), also known as Fahr's disease, is a rare autosomal dominant or recessive neurodegenerative disorder characterized by bilateral and symmetrical microvascular calcifications affecting multiple brain regions, particularly the basal ganglia (globus pallidus, caudate nucleus, and putamen) and thalamus. The most common clinical manifestations include cognitive impairment, neuropsychiatric signs, and movement disorders. Loss-of-function mutations in SLC20A2 are the major genetic causes of PFBC. Objective: This study aimed to investigate whether Slc20a2 knockout mice could recapitulate the dynamic processes and patterns of brain calcification and neurological symptoms in patients with PFBC. We comprehensively evaluated brain calcifications and PFBC-related behavioral abnormalities in Slc20a2 -deficient mice. Methods: Brain calcifications were analyzed using classic calcium-phosphate staining methods. The Morris water maze, Y-maze, and fear conditioning paradigms were used to evaluate long-term spatial learning memory, working memory, and episodic memory, respectively. Sensorimotor gating was mainly assessed using the prepulse inhibition of the startle reflex program. Spontaneous locomotor activity and motor coordination abilities were evaluated using the spontaneous activity chamber, cylinder test, accelerating rotor-rod, and narrowing balance beam tests. Results: Slc20a2 homozygous knockout (Slc20a2 -HO) mice showed congenital and global developmental delay, lean body mass, skeletal malformation, and a high proportion of unilateral or bilateral eye defects. Brain calcifications were detected in the hypothalamus, ventral thalamus, and midbrain early at postnatal day 80 in Slc20a2 -HO mice, but were seldom found in Slc20a2 heterozygous knockout (Slc20a2 -HE) mice, even at extremely old age. Slc20a2 -HO mice exhibited spatial learning memory impairments and sensorimotor gating deficits while exhibiting normal working and episodic memories. The general locomotor activity, motor balance, and coordination abilities were not statistically different between Slc20a2 -HO and wild-type mice after adjusting for body weight, which was a major confounding factor in our motor function evaluations. Conclusion: The human PFBC-related phenotypes were highly similar to those in Slc20a2 -HO mice. Therefore, Slc20a2 -HO mice might be suitable for the future evaluation of neuropharmacological intervention strategies targeting cognitive and neuropsychiatric impairments. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC) is a neurological condition characterized by the presence of intracranial calcifications, mainly involving basal ganglia, thalamus, and dentate nuclei. So far, six genes have been linked to this condition: SLC20A2, PDGFRB, PDGFB, and XPR1 inherited as autosomal-dominant trait, while MYORG and JAM2 present a recessive pattern of inheritance. Patients mainly present with movement disorders, psychiatric disturbances, and cognitive decline or are completely asymptomatic and calcifications may represent an occasional finding. Here we present three variants in SLC20A2, two exonic and one intronic, which we found in patients with PFBC associated to three different clinical phenotypes. One variant is novel and two were already described as variants of uncertain significance. We confirm the pathogenicity of these three variants and suggest a broadening of the phenotypic spectrum associated with mutations in SLC20A2. [ABSTRACT FROM AUTHOR]

A patient with Parkinson's disease (PD) who was examined as a candidate for DBS was initially rejected due to extensive brain calcifications. Upon second opinion and planning of trajectories she underwent successful surgery. Genetic analyses identified a mutation in SLC20A2, a gene known to cause brain calcifications, but no mutation known to cause PD was found. [ABSTRACT FROM AUTHOR]

Background: Idiopathic basal ganglia calcification (IBGC) is a genetic disorder characterized by bilateral basal ganglia calcification and neural degeneration. In this study, we reported a new SLC2OA2 mutation of IBGC and reviewed relevant literature to explore the association between phenotypes and genotypes in Chinese IBGC patients. Methods: Clinical information of the proband and her relatives were collected comprehensively. Blood samples of both the patient and her father were obtained, and genetic screening related to IBGC was performed using second generation sequencing with their consent. Findings were confirmed by Sanger sequencing. Polyphen-2 was used to predict the potential association between mutations and disease. Then, we retrieved literatures of Chinese IBGC patients and explored the association between phenotype and genotype. Results: A novel mutation was identified through genetic testing, and it is suggested to be a damage mutation predicted by Polyphen-2. Through literature review, we found that SLC20A2 mutation is the most common cause for IBGC in China. Its hot spot regions are mainly on the 1st and 8th exons; the second common one is PDGFB where the hot spot covered a length of 220–230 bp localized on the 2nd exon; moreover, Chinese IBGC patients featured early-onset, more severe movement disorder and relatively mild cognitive impairment compared with those in other countries. Conclusions: There is significant heterogeneity both in phenotype and genotype in Chinese IBGC patients. Further research of pathogenic mechanism of IBGC is required to eventually develop precise treatment for individuals who suffered this disease.

Objective: Primary familial brain calcification (PFBC) is a rare cerebral microvascular calcifying disorder with diverse neuropsychiatric expression. Five genes were reported as PFBC causative when carrying pathogenic variants. Haploinsufficiency of SLC20A2, which encodes an inorganic phosphate importer, is a major cause of autosomal-dominant PFBC. However, PFBC remains genetically unexplained in a proportion of patients, suggesting the existence of additional genes or cryptic mutations. We analyzed exome sequencing data of 71 unrelated, genetically unexplained PFBC patients with the aim to detect copy number variations that may disrupt the expression of core PFBC-causing genes.Methods: After the identification of a deletion upstream of SLC20A2, we assessed its consequences on gene function by reverse transcriptase droplet digital polymerase chain reaction (RT-ddPCR), an ex vivo inorganic phosphate uptake assay, and introduced the deletion of a putative SLC20A2 enhancer mapping to this region in human embryonic kidney 293 (HEK293) cells by clustered regularly interspaced short palindromic repeats (CRISPR) - CRISPR-associated protein 9 (Cas9).Results: The 8p11.21 deletion, segregating with PFBC in a family, mapped 35 kb upstream of SLC20A2. The deletion carriers/normal controls ratio of relative SLC20A2 mRNA levels was 60.2% (P < 0.001). This was comparable with that of patients carrying an SLC20A2 premature stop codon (63.4%; P < 0.001). The proband exhibited a 39.3% decrease of inorganic phosphate uptake in blood (P = 0.015). In HEK293 cells, we observed a 39.8% decrease in relative SLC20A2 mRNA levels after normalization on DNA copy number (P < 0.001).Discussion: We identified a deletion of an enhancer of SLC20A2 expression, with carriers showing haploinsufficiency in similar ranges to loss-of-function alleles, and we observed reduced mRNA levels after deleting this element in a cellular model. We propose a 3-step strategy to identify and easily assess the effect of such events. © 2020 International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Idiopathic basal ganglia calcification (IBGC) or primary familial brain calcification is a rare genetic condition characterized by an autosomal dominant inheritance pattern and the presence of bilateral calcifications in the basal ganglia, thalami, cerebellum and cerebral subcortical white matter. The syndrome is genetically and phenotypically heterogeneous. Causal mutations have been identified in four genes: SLC20A2, PDGFRB, PDGFB and XPR1. A variety of progressive neurological and psychiatric symptoms have been described, including cognitive impairment, movement disorders, bipolar disorder, chronic headaches and migraine, and epilepsy. Here we describe a family with a novel SLC20A2 mutation mainly presenting with neurological symptoms including cortical myoclonus and epilepsy. While epilepsy, although rare, has been reported in patients with IBGC associated with SLC20A2 mutations, cortical myoclonus seems to be a new manifestation. [ABSTRACT FROM AUTHOR]

• A rare splicing mutation related to PFBC in SLC20A2 (c.730 + 1G > A) was found. • The splicing mutation leads to exon 6 skipping in SLC20A2. • The mutation results in a 39 amino acid deletion in SLC20A2 protein. Primary familial brain calcification (PFBC) is a rare degenerative disease characterized by symmetrical bilateral calcinosis in the basal ganglia and other brain regions. It has an autosomal dominant inheritance pattern in most cases and exhibits genetic heterogeneity. Previous studies reported that SLC20A2, PDGFRB, PDGFB , XPR1 and MYORG are associated with PFBC, with SLC20A2 the main culprit. However, other mutations may also cause PFBC. Here, we performed a study to reveal the contributing mutations that gave rise to PFBC in a Chinese PFBC family. We recruited a PFBC family consisting of eight patients and eight healthy family members across three generations. Whole-exome sequencing, Sanger sequencing and RT-PCR were used to detect the genetic mutations. Whole-exome sequencing revealed that c.730 + 1G > A of SLC20A2 was the candidate pathogenic mutation for the proband in this family. Genomic DNA PCR amplification and Sanger sequencing confirmed that all the patients from the family carried this mutation, while the healthy subjects in the family did not. Complementary DNA (cDNA) PCR amplification and Sanger sequencing confirmed that the patients had a mutation that caused exon 6 skipping in SLC20A2. We identified a SLC20A2 splicing variant (c.730 + 1G > A) in a PFBC family. This mutation led to an alternative splicing event that skipped exon 6 in SLC20A2. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC) is a rare neurological disorder. Mutations in five genes (SLC20A2, PDGFRB, PDGFB, XPR1, and MYORG) have been linked to PFBC. Here, we used SYBR green‐based real‐time quantitative polymerase chain reaction (PCR) assay and denaturing high‐performance liquid chromatography analysis to detect copy number variants (CNVs) in 20 unrelated patients with PFBC, negatively sequenced for the five known genes. We identified three deletions in SLC20A2, including a large de novo full gene deletion and two exonic deletions confined to exon 2 and exon 6, respectively. Subsequent linked‐read whole‐genome sequencing of the patient with the large deletion showed a 1.7 Mb heterozygous deletion which removed the entire coding regions of SLC20A2 as well as 21 other genes. In the family with a deletion of exon 6, a missense variant of uncertain significance (SLC20A2: p.E267Q) also co‐segregated with the disease. Functional assay showed the deletion could result in significantly impaired phosphate transport, whereas the p.E267Q variant did not. Our results confirm that deletion in SLC20A2 is a causal mechanism for PFBC and highlight the importance of functional study for classifying a rare missense variant as (likely) pathogenic. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC) is a rare neurodegenerative disorder with four causative genes (SLC20A2, PDGFRB, PDGFB, and XPR1) that have been identified. Here, we aim to describe the mutational spectrum of four causative genes in a series of 226 unrelated Chinese PFBC patients. Mutations in four causative genes were detected in 16.8% (38/226) of PFBC patients. SLC20A2 mutations accounted for 14.2% (32/226) of all patients. Mutations in the other three genes were relatively rare, accounting for 0.9% (2/226) of all patients, respectively. Clinically, 44.8% of genetically confirmed patients (probands and relatives) were considered symptomatic. The most frequent symptoms were chronic headache, followed by movement disorders and vertigo. Moreover, the total calcification score was significantly higher in the symptomatic group compared to the asymptomatic group. Functionally, we observed impaired phosphate transport induced by seven novel missense mutations in SLC20A2 and two novel mutations in XPR1. The mutation p.D164Y in XPR1 might result in low protein expression through an enhanced proteasome pathway. In conclusion, our study further confirms that mutations in SLC20A2 are the major cause of PFBC and provides additional evidence for the crucial roles of phosphate transport impairment in the pathogenies of PFBC. We made a genetic diagnosis in 16.8% of PFBC probands and identified 30 mutations; Mutations in SLC20A2 are the major cause of PFBC, while the other three genes are relatively rare; Our findings also strongly support crucial roles of phosphate transport impairment in the pathogenies of PFBC. [ABSTRACT FROM AUTHOR]

Abstract Idiopathic Basal Ganglia Calcification (IBGC) is a rare neuropsychiatric illness also known as Fahr's disease or Primary Familial Brain Calcification (PFBC). IBGC is caused by SLC20A2 variants, which encodes the inorganic phosphate (Pi) transporter PiT-2, a transmembrane protein associated with Pi homeostasis. We have reported novel SLC20A2 variants in the Japanese population and established an induced pluripotent stem cells (iPSCs) from an IBGC patient carrying a SLC20A2 variant. To investigate the effect of these SLC20A2 variants identified in our previous study, we used Chinese hamster ovary (CHO) cells expressing these variant proteins using the Flp-In system (Flp-In CHO cells), and showed that variant SLC20A2 proteins significantly disrupted the Pi transport activity in Flp-In CHO cells. Endothelial cells (ECs) represent important target cells for elucidating the pathology of IBGC. Using patient-derived iPSCs in this study, we differentiated these cells into ECs and found no significant difference in their differentiation capacity into ECs compared with control iPSCs. However, the Pi transport activity of IBGC patient-derived iPS-ECs was significantly decreased compared with that of control iPS-ECs without changing the gene expression of the other SLC 20 family members. We confirmed that SLC20A2 variants caused the loss of function of the Pi transport activity in both Flp-In CHO cells and disease-specific iPSCs. This is the first report to show an in vitro model of iPSCs in IBGC with patient-identified SLC20A2 variants. These useful tools will help in elucidating IBGC pathogenesis and can be used for screening drug candidates. Highlights • The SLC20A2 variants with IBGC cause the loss of function for the Pi transport activity. • The Pi transport was triggered by a mechanism different from membrane translocation. • The Pi transport activity was reduced in IBGC patient-derived iPS-ECs. • The tool using iPSCs will be very useful for elucidating IBGC pathogenesis. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC) is a rare neurodegenerative disorder characterized by symmetrical and bilateral brain calcification. It is typically inherited as an autosomal dominant disorder, and de novo variants have also been described. Interestingly, just recent studies have reported the first autosomal recessive PFBC-causative gene. PFBC patients exhibit high clinical heterogeneity including Parkinsonism, dystonia, ataxia, depression, and migraine. Mice studies, an important research tool, have been a breakthrough in increasing the understanding of PFBC's main signs and symptoms, and many findings reported in these mice have been subsequently reported in patients. One phenotype that has been observed in PFBC mice models but not in PFBC patients, however, is the development of ophthalmic abnormalities. This way, this report focused on performing an ophthalmic assessment in six Brazilian patients genetically diagnosed with PFBC. The assessments showed that none of the PFBC individuals included presented any of the ophthalmic abnormalities reported in mice models, such as cataracts, ocular calcification, abnormal iris and lens morphology, and retinal deterioration. Additionally, of the six PFBC patients described, two SLC20A2 mutation carriers showed physiological excavation of the optic nerve head and partial vitreous detachment, while just one individual presented bilateral narrowing of retinal arterioles. In summary, no evidence of similar ophthalmological abnormalities found in mice were found in our patients; nonetheless, further studies in larger sample size are warranted to corroborate with our findings. To our knowledge, this study is the first to focus on investigating, in PFBC patients, the ophthalmological phenotypes described in the PFBC mice models. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC), widely known as Fahr's disease, is a rare disorder caused by pathogenic variants in SLC20A2, PDGFB, PDGFRB, XPR1, or MYORG genes. It is characterized by ectopic brain calcification, mostly affecting basal ganglia, thalamus, and cerebellum. PFBC patients can present a wide spectrum of symptoms including cognitive, neuropsychiatric, and motor alterations. However, it is well established that PFBC individuals also present high clinical heterogeneity, though the genetic cause of this phenotypic is not understood. Recently, Wang et al. (Front Cell Neurosci. 10.3389/fncel.2019.00250, 2019) reported on the role of MEA6 gene in cerebellar development and motor performance, also citing that MEA6 might be linked to PFBC. A MEA6 variant was described in 2007 as a PFBC candidate gene in an American family. However, this family was later linked to the SLC20A2 gene discarding the MEA6 as a PFBC-gene and also some members were confirmed as phenocopy. Additionally, five independent studies have been shown that variants in a second gene, not related to PFBC, were identified in PFBC patients, promoting a complex and heterogeneous phenotype. Thus, further investigation is required to explain whether and how MEA6 contributes to the clinical presentation in this American family. Finally, this letter highlights the possible digenic influence on clinical heterogeneity of PFBC patients, and such a possibility might advance our understanding of PFBC phenotypes. [ABSTRACT FROM AUTHOR]

It has been recently reported that mutations inSLC20A2gene are a major cause of primary familial brain calcifications, a rare neurodegenerative disorder characterized by symmetrical and bilateral intracranial calcification. We conducted a pedigree study by performing next Generation Sequencing in a Chinese family with three generations. Three members in this family developed Parkinsonism in their sixth decade, also, the proband presented with schizophrenia for 40 years. Next Generation Sequencing identified a novel nonsense heterozygous substitution c.1158C > A (p.Thr 386 ) ofSLC20A2gene, introducing a stop codon in exon 10. The mutation was present in symptomatic and asymptomatic individuals with intracranial calcification, but absent in the individual without calcification, suggesting the mutation segregates with brain calcification. mRNA expression was decreased by 35% in the proband. We are the first to demonstrate a novel c.1158C > A mutation ofSLC20A2gene in a Chinese family with primary familial brain calcifications. [ABSTRACT FROM AUTHOR]

Objectives Primary familial brain calcification ( PFBC) is a rare neurological disease often inherited as a dominant trait. Mutations in four genes ( SLC20A2, PDGFB, PDGFRB, and XPR1) have been reported in patients with PFBC. Of these, point mutations or small deletions in SLC20A2 are most common. Thus far, only one large deletion covering entire SLC20A2 and several smaller, exonic deletions of SLC20A2 have been reported. The aim of this study was to identify the causative gene defect in a Finnish PFBC family with three affected patients. Materials and methods A Finnish family with three PFBC patients and five unaffected subjects was studied. Sanger sequencing was used to exclude mutations in the coding and splice site regions of SLC20A2, PDGFRB, and PDGFB. Whole-exome ( WES) and whole-genome sequencing ( WGS) were performed to identify the causative mutation. A SNP array was used in segregation analysis. Results Copy number analysis of the WGS data revealed a heterozygous deletion of ~578 kb on chromosome 8. The deletion removes the 5′ UTR region, the noncoding exon 1 and the putative promoter region of SLC20A2 as well as the coding regions of six other genes. Conclusions Our results support haploinsufficiency of SLC20A2 as a pathogenetic mechanism in PFBC. Analysis of copy number variations ( CNVs) is emerging as a crucial step in the molecular genetic diagnostics of PFBC, and it should not be limited to coding regions, as causative variants may reside in the noncoding parts of known disease-associated genes. [ABSTRACT FROM AUTHOR]

Introduction: There are now a number genes, known to be associated with familial primary brain calcification (PFBC), causing the so called 'Fahr's' disease or syndrome. These are SCL20A2, PDGFB, PDGFRB and XPR1. In this systematic review, we analyse the clinical and radiological features reported in genetically confirmed cases with PFBC. We have additionally reviewed pseudohypoparathyroidism which is a close differential diagnosis of PFBC in clinical presentation and is also genetically determined.Methods: We performed a Medline search, from 1st Jan 2012 through to 7th November 2016, for publications with confirmed mutations of SCL20A2, PDGFB, PDGFRB, and XPR1 and found twenty papers with 137 eligible cases. A second search was done for publications of cases with Pseudohypoparathyroidism or pseudopseudohypoparathyroidism, and found 18 publications with 20 eligible cases.Results: SLC20A2 was the most common gene involved with 75 out of 137 cases included with PFBC (55%) followed by PDGFB (31%) and PDGFRB (11%). Statistically significant correlation was found between the presence of parkinsonism with SLC20A2 mutations, headache in PDGFB and generalised tonic-clonic seizures in patients with pseudohypoparathyroidism.Conclusion: We combine statistical analysis and clinical inference to suggest a diagnostic algorithm based on the observations in this study to help with investigation of a patient with neurological features and brain calcification. [ABSTRACT FROM AUTHOR]

Primary brain calcification (PBC) is a neurodegenerative disorder characterized by calcium-phosphate deposits in the basal ganglia and often also other areas of the brain. The prevalent clinical manifestations are cognitive impairment, neuropsychiatric symptoms, and movement disorders. In recent years, monoallelic variants in SLC20A2, which encodes the type III sodium-dependent inorganic phosphate (P) transporter 2 (PiT2), have been linked to the familial form of PBC in 40-50% of the families reported worldwide as well as to sporadic cases of PBC. Further insight into the disease mechanism is, however, needed. Based on co-expression studies of wild-type and variant PiT2 in Xenopus laevis oocytes, the molecular disease mechanism associated with SLC20A2 missense variants has formerly been suggested to be haploinsufficiency. We have here used mammalian cells isolated from a Slc20a2 mouse and co-expression of human wild-type and variant PiT2. Two of the variants studied have both been reported twice in unrelated PBC cases: PiT2D28N in two sporadic cases and PiT2E575K in a familial and a sporadic case. We find that in mammalian cells, the analyzed SLC20A2 missense variants can exert their effect in a dominant negative manner resulting in decreased wild-type PiT2 P transport. Thus, compared to monoallelic lack of functional PiT2 protein expression, which reasonably points towards haploinsufficiency, certain SLC20A2 missense variants may be more detrimental for cellular P uptake and potentially contribute to an earlier disease onset and/or a more severe phenotype as observed for Slc20a2 mice compared to Slc20a2 mice. [ABSTRACT FROM AUTHOR]

Idiopathic basal ganglia calcification is a brain calcification disorder that has been genetically linked to autosomal dominant mutations in the sodium-dependent phosphate co-transporter, SLC20A2. The mechanisms whereby deficiency of Slc20a2 leads to basal ganglion calcification are unknown. In the mouse brain, we found that Slc20a2 was expressed in tissues that produce and/or regulate cerebrospinal fluid, including choroid plexus, ependyma and arteriolar smooth muscle cells. Haploinsufficient Slc20a2 +/− mice developed age-dependent basal ganglia calcification that formed in glymphatic pathway-associated arterioles. Slc20a2 deficiency uncovered phosphate homeostasis dysregulation characterized by abnormally high cerebrospinal fluid phosphate levels and hydrocephalus, in addition to basal ganglia calcification. Slc20a2 siRNA knockdown in smooth muscle cells revealed increased susceptibility to high phosphate-induced calcification. These data suggested that loss of Slc20a2 led to dysregulated phosphate homeostasis and enhanced susceptibility of arteriolar smooth muscle cells to elevated phosphate-induced calcification. Together, dysregulated cerebrospinal fluid phosphate and enhanced smooth muscle cell susceptibility may predispose to glymphatic pathway-associated arteriolar calcification. [ABSTRACT FROM AUTHOR]

Background: Linkage analyses of families with primary familial brain calcification (formerly idiopathic basal ganglia calcification [IBGC]) identified 3 candidate loci (IBGC1-3). Recently, SLC20A2 mutations were found in the IBGC1 and IBGC3 families, merging these 2 loci. We here elucidate the genetic cause of primary familial brain calcification in the 'IBGC2' kindred.Methods: We sequenced known primary familial brain calcification genes and quantified SLC20A2 and PDGFB. Moreover, CT scans of affected and unaffected family members were evaluated by 2 blinded neuroradiologists for distribution of brain calcification.Results: A heterozygous multiexonic SLC20A2 deletion was detected in several affected family members. A reevaluation of neuroimaging data revealed a subset of mutation-negative individuals with only mild and/or unilateral calcification.Conclusions: The identified SLC20A2 mutation resolves the genetic cause of primary familial brain calcification in the 'IBGC2' kindred, collapsing 'IBGC2' into IBGC1. We suggest an algorithm for predicting the chances of finding genetic mutations that has to be validated in further studies. Our study enhances criteria for the evaluation of neuroimaging data, contributing further to the much needed harmonization of diagnostic and research data collection in primary familial brain calcification. © 2016 International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Highlights • We present a Japanese family with primary familial brain calcification (PFBC). • Whole-exome sequencing identified a novel frameshift mutation in SLC20A2. • The proband presented with a transient ischemic attack (TIA). • PFBC may be associated with secondary ischemic stroke, including TIA. [ABSTRACT FROM AUTHOR]

Idiopathic basal ganglia calcification (IBGC), or Fahr's disease, is a neurological disorder characterized by widespread calcification in the brain. Recently, several causative genes have been identified, but the histopathologic features of the brain lesions and expression of the gene products remain unclear. Here, we report the clinical and autopsy features of a 62-year-old Japanese man with familial IBGC, in whom an SLC20A2 mutation was identified. The patient developed mild cognitive impairment and parkinsonism. A brain CT scan demonstrated abnormal calcification in the bilateral basal ganglia, thalami and cerebellum. An MRI study at this point revealed glioblastoma, and the patient died 6 months later. At autopsy, symmetric calcification in the basal ganglia, thalami, cerebellar white matter and deeper layers of the cerebral cortex was evident. The calcification was observed in the tunica media of small arteries, arterioles and capillaries, but not in veins. Immunohistochemistry using an antibody against type III sodium-dependent phosphate transporter 2 (PiT-2), the SLC20A2 product, demonstrated that astrocytic processes were labeled in several regions in control brains, whereas in the patient, reactivity in astrocytes was apparently weak. Immunoblotting demonstrated a marked decrease of PiT-2 in the patient. There are few autopsy reports of IBGC patients with confirmation of the genetic background. The autopsy features seem informative for better understanding the histogenesis of IBGC lesions. [ABSTRACT FROM AUTHOR]

Mutations in the SLC20A2-gene encoding the inorganic phosphate (Pi) transporter PiT2 can explain approximately 40 % of the familial cases of the rare neurodegenerative disorder primary familial brain calcification (Fahr's disease). The disease characteristic, cerebrovascular-associated calcifications, is also present in Slc20a2-knockout (KO) mice. Little is known about the specific role(s) of PiT2 in the brain. Recent in vitro studies, however, suggest a role in regulation of the [Pi] in cerebrospinal fluid (CSF). We here show that Slc20a2-KO mice indeed have a high CSF [Pi] in agreement with a role of PiT2 in Pi export from the CSF. The implications in relation to disease mechanism are discussed. [ABSTRACT FROM AUTHOR]

Primary familial brain calcification (PFBC), otherwise known as Fahr's disease, is a rare autosomal dominant condition with manifestations of movement disorders, neuropsychiatric symptoms, and epilepsy in a minority of PFBC patients. The clinical presentation of epilepsy in PFBC has not been described in detail. We present a paediatric patient with PFBC and refractory focal epilepsy based on seizure semiology and ictal EEG, but with generalized interictal EEG abnormalities. The patient was found to have a SLC20A2 mutation known to be pathogenic in PFBC, as well as a variant of unknown significance in SCN2A. This case demonstrates that the ictal EEG is important for accurately classifying epilepsy in affected subjects with PFBC. Further, epilepsy in PFBC may be a polygenic disorder. [ABSTRACT FROM AUTHOR]