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Kinesins are motor proteins involved in microtubule (MT)-mediated intracellular transport. They contribute to key cellular processes, including intracellular trafficking, organelle dynamics and cell division. Pathogenic variants in kinesin-encoding genes underlie several human diseases characterized by an extremely variable clinical phenotype, ranging from isolated neurodevelopmental/neurodegenerative disorders to syndromic phenotypes belonging to a family of conditions collectively termed as ‘ciliopathies.’ Among kinesins, kinesin-1 is the most abundant MT motor for transport of cargoes towards the plus end of MTs. Three kinesin-1 heavy chain isoforms exist in mammals. Different from KIF5A and KIF5C, which are specifically expressed in neurons and established to cause neurological diseases when mutated, KIF5B is an ubiquitous protein. Three de novo missense KIF5B variants were recently described in four subjects with a syndromic skeletal disorder characterized by kyphomelic dysplasia, hypotonia and DD/ID. Here, we report three dominantly acting KIF5B variants (p.Asn255del, p.Leu498Pro and p.Leu537Pro) resulting in a clinically wide phenotypic spectrum, ranging from dilated cardiomyopathy with adult-onset ophthalmoplegia and progressive skeletal myopathy to a neurodevelopmental condition characterized by severe hypotonia with or without seizures. In vitro and in vivo analyses provide evidence that the identified disease-associated KIF5B variants disrupt lysosomal, autophagosome and mitochondrial organization, and impact cilium biogenesis. All variants, and one of the previously reported missense changes, were shown to affect multiple developmental processes in zebrafish. These findings document pleiotropic consequences of aberrant KIF5B function on development and cell homeostasis, and expand the phenotypic spectrum resulting from altered kinesin-mediated processes.

Background: Inactivating NSD1 mutations causing Sotos syndrome have been previously associated with a specific genome-wide DNA methylation (DNAm) pattern. Sotos syndrome is characterized by phenotypic overlap with other overgrowth syndromes, and a definite diagnosis might not be easily reached due to the high prevalence of variants of unknown significance (VoUS) that are identified in patients with a suggestive phenotype. Objective: we performed microarray DNAm profiling in a set of 11 individuals with a clinical suspicion of Sotos syndrome and carrying an NSD1 VoUS or previously unreported variants to solve uncertainty in defining pathogenicity of the observed variants. The impact of the training cohort size on sensitivity and prediction confidence of the classifier was assessed. Results: The Sotos syndrome-specific DNAm signature was validated in six individuals with a clinical diagnosis of Sotos syndrome and carrying bona fide pathogenic NSD1 variants. Applying this approach to the remaining 11 individuals with NSD1 variants, we succeeded in confirming pathogenicity in eight subjects and excluding the diagnosis of Sotos syndrome in three. The sensitivity and prediction confidence of the classifier based on the different sizes of the training sets did not show substantial differences, though the overall performance was improved by using a data balancing strategy. Conclusions: The present approach solved uncertainty in cases with NDS1 VoUS, further demonstrating the clinical utility of DNAm profiling.

Mutations in the MED13 gene are reported in the literature in association with clinically variable, neurodevelopmental disorders, which are characterized by mild-to-severe intellectual disability, autism spectrum disorder, attention deficit/hyperactivity disorder, epilepsy, ocular or skeletal abnormalities, congenital cardiac defects, and facial dysmorphisms. Here, we report a patient with an epileptic phenotype carrying a novel missense mutation characterized by developmental and epileptic encephalopathy with infantile spasms.Through trio-based WES, we identified a novel de novo heterozygous missense variant c.2501AG in the MED13 gene. We reviewed all medical charts of the present patient and reviewed all previously reported cases with pathogenic variants of MED13.This study involves a 24-month-old boy with epilepsy onset at the age of 3 months with drug-resistant focal seizures followed by infantile spasms at the age of 10 months. He had a severe, developmental delay along with microcephaly and dysmorphic features. From a literature review, it emerged that epilepsy is described in only one out of nineteen of previously reported patients with a phenotype of generalized, drug-resistant epilepsy with myoclonic-atonic seizures. Microcephaly, developmental delay, hypotonia, corpus callosum abnormalities, deafness, and retinal atrophy were common features in the previously described cases.This case expands the genetic landscape of infantile spasms as well as the phenotype of MED13-related disorders adding the electroclinical features of early-onset developmental and epileptic encephalopathy with infantile spasms to the previously described, generalized epilepsy with myoclonic-atonic seizures.

Germline pathogenic variants in AMER1 cause osteopathia striata with cranial sclerosis (OSCS: OMIM 300373), an X-linked sclerosing bone disorder. Female heterozygotes exhibit metaphyseal striations in long bones, macrocephaly, cleft palate, and, occasionally, learning disability. Male hemizygotes typically manifest the condition as fetal or neonatal death. Somatically acquired variants in AMER1 are found in neoplastic tissue in 15-30% of patients with Wilms tumor; however, to date, only one individual with OSCS has been reported with a Wilms tumor. Here we present four cases of Wilms tumor in unrelated individuals with OSCS, including the single previously published case. We also report the first case of bilateral Wilms tumor in a patient with OSCS. Tumor tissue analysis showed no clear pattern of histological subtypes. In Beckwith-Wiedemann syndrome, which has a known predisposition to Wilms tumor development, clinical protocols have been developed for tumor surveillance. In the absence of further evidence, we propose a similar protocol for patients with OSCS to be instituted as an initial precautionary approach to tumor surveillance. Further evidence is needed to refine this protocol and to evaluate the possibility of development of other neoplasms later in life, in patients with OSCS.

Purpose GRIA3, encoding subunit 3 of glutamate ionotropic AMPA receptor, is associated with X-linked intellectual disability (ID), dysmorphic features, and non-syndromic epilepsy. We aimed to characterize electro-clinical features of patients with GRIA3 variants. Methods We report a patient carrying a hemizygous missense variant c.2359 G > A (p.Glu787Lys) inGRIA3 gene. Following a literature search, we also reviewed clinical, electrophysiological, radiological, and genetic features of 19 patients with GRIA3 mutations. Results This 26-month-old boy had developmental delay, early onset refractory myoclonic epilepsy, and non-convulsive refractory status epilepticus. In published reports, epilepsy was in 6 of 19 patients carrying different genotypes, though epilepsy and electroencephalogram features were not completely defined. Out of the 6 patients, one presented with generalized tonic-clonic seizures, two with myoclonic and clonic events (one also presented with epileptic spasms), and one with atypical absences and myoclonic jerks. Information on type of epilepsy was unavailable for 3 cases. Epilepsy onset was early in life and there was potential tendency for myoclonic/clonic events. The epilepsy was difficult to treat and prognosis is poor. Severity of ID ranged from mild to severe and was variably associated with bipolar affective disorder and autistic spectrum disorders. Other neurological features included hypotonia, asthenic body habitus with poor muscle bulk, and hyporeflexia. Conclusion Our report expands knowledge on the electro-clinical and molecular spectrum of GRIA3 variants. Larger investigations will better define the prevalence of epilepsy, the epileptic phenotype, and syndromic features underlying GRIA3 variants.

The endocannabinoid system is a highly conserved and ubiquitous signalling pathway with broad-ranging effects. Despite critical pathway functions, gene variants have not previously been conclusively linked to human disease. We identified nine children from eight families with heterozygous, de novo truncating variants in the last exon of DAGLA with a neuro-ocular phenotype characterized by developmental delay, ataxia and complex oculomotor abnormality. All children displayed paroxysms of nystagmus or eye deviation accompanied by compensatory head posture and worsened incoordination most frequently after waking. RNA sequencing showed clear expression of the truncated transcript and no differences were found between mutant and wild-type DAGLA activity. Immunofluorescence staining of patient-derived fibroblasts and HEK cells expressing the mutant protein showed distinct perinuclear aggregation not detected in control samples. This report establishes truncating variants in the last DAGLA exon as the cause of a unique paediatric syndrome. Because enzymatic activity was preserved, the observed mislocalization of the truncated protein may account for the observed phenotype. Potential mechanisms include DAGLA haploinsufficiency at the plasma membrane or dominant negative effect. To our knowledge, this is the first report directly linking an endocannabinoid system component with human genetic disease and sets the stage for potential future therapeutic avenues.

BackgroundJoubert syndrome (JS) is a neurodevelopmental ciliopathy characterised by a distinctive mid-hindbrain malformation, the ‘molar tooth sign’. Over 40 JS-associated genes are known, accounting for two-thirds of cases.MethodsWhile most variants are novel or extremely rare, we report on 11 recurring variants in seven genes, including three known ‘founder variants’ in the Ashkenazi Jewish, Hutterite and Finnish populations. We evaluated variant frequencies in ~550 European patients with JS and compared them with controls (>15 000 Italian plus gnomAD), and with an independent cohort of ~600 JS probands from the USA.ResultsAll variants were markedly enriched in the European JS cohort compared with controls. When comparing allele frequencies in the two JS cohorts, the Ashkenazim founder variant (TMEM216c.218G>T) was significantly enriched in American compared with European patients with JS, whileMKS1c.1476T>G was about 10 times more frequent among European JS. Frequencies of other variants were comparable in the two cohorts. Genotyping of several markers identified four novel European founder haplotypes.Two recurrent variants (MKS1c.1476T>G andKIAA0586c.428delG), have been detected in homozygosity in unaffected individuals, suggesting they could act as hypomorphic variants. However, while fibroblasts from aMKS1c.1476T>G healthy homozygote showed impaired ability to form primary cilia and mildly reduced ciliary length, ciliary parameters were normal in cells from aKIAA0586c.428delG healthy homozygote.ConclusionThis study contributes to understand the complex genetic landscape of JS, explain its variable prevalence in distinct geographical areas and characterise two recurrent hypomorphic variants.

The finding of USP9X variants in females has been associated with female-restricted X-linked mental retardation (MRXS99F), a rare syndrome featured by developmental delay and distinct congenital anomalies. Here, we report a female fetus with MRXS99F due to a novel frameshift variant, c.6679_6685delAAATTATinsTCCTG (p.Lys2227SerfsTer2) in USP9X, which was present in a mosaic state in the amniocytes and in the peripheral blood after birth (14% and 30%, respectively). The X methylation status analysis displayed a partially skewed X-inactivation with 80% of inactive paternal X. The first signs of the MRXS99F were prenatally detected at 20 weeks, with an enlarged posterior cranial fossa, an upward rotation of the cerebellar vermis and partial corpus callosum agenesis, together with a cardiac septal defect and a single umbilical artery. After birth and during postnatal follow-up the anal anteriorization and the presence of a bilateral membranous choanal atresia were noted, whereas the MRI revealed the hypo/aplasia of the olfactory bulbs, a widening of the subarachnoid spaces and a delay in the myelinisation. During the 18-months follow-up a severe growth and global developmental delay, together with a bilateral moderate deafness with a threshold at 40 dB, dental enamel erosions and an initial scoliosis were observed. We report the prenatal and postnatal features of a classical MRXS99F phenotype and a mosaic USP9X frameshift variant with a partially skewed X inactivation and discuss genotype/phenotype correlations in view of the published studies so far.

Biallelic mutations in the BRAT1 gene, encoding BRCA1-associated ATM activator 1, result in variable phenotypes, from rigidity and multifocal seizure syndrome, lethal neonatal to neurodevelopmental disorder, and cerebellar atrophy with or without seizures, without obvious genotype-phenotype associations. We describe two families at the mildest end of the spectrum, differing in clinical presentation despite a common genotype at the BRAT1 locus. Two siblings displayed nonprogressive congenital ataxia and shrunken cerebellum on magnetic resonance imaging. A third unrelated patient showed normal neurodevelopment, adolescence-onset seizures, and ataxia, shrunken cerebellum, and ultrastructural abnormalities on skin biopsy, representing the mildest form of NEDCAS hitherto described. Exome sequencing identified the c.638dup and the novel c.1395G>A BRAT1 variants, the latter causing exon 10 skippings. The p53-MCL test revealed normal ATM kinase activity. Our findings broaden the allelic and clinical spectrum of BRAT1-related disease, which should be suspected in presence of nonprogressive cerebellar signs, even without a neurodevelopmental disorder.

To determine the neuroimaging pattern of cerebellar dysplasia (CD) and other posterior fossa morphological anomalies associated with mutations in tubulin genes and to perform clinical and genetic correlations. Twenty-eight patients harbouring 23 heterozygous pathogenic variants (ten novel) in tubulin genes TUBA1A (n = 10), TUBB2B (n = 8) or TUBB3 (n = 5) were studied by a brain MRI scan performed either on a 1.5 T (n = 10) or 3 T (n = 18) MR scanner with focus on the posterior fossa. Cerebellar anomalies were detected in 24/28 patients (86%). CD was recognised in 19/28 (68%) including cortical cerebellar dysplasia (CCD) in 18/28, either involving only the cerebellar hemispheres (12/28) or associated with vermis dysplasia (6/28). CCD was located only in the right hemisphere in 13/18 (72%), including four TUBB2B-, four TUBB3- and five TUBA1A-mutated patients, while in the other five TUBA1A cases it was located only in the left hemisphere or in both hemispheres. The postero-superior region of the cerebellar hemispheres was most frequently affected. The cerebellar involvement in tubulinopathies shows specific features that may be labelled as ‘tubulin-related CD’. This pattern is unique and differs from other genetic causes of cerebellar dysplasia. • Cortical cerebellar dysplasia without cysts is suggestive of tubulin-related disorder. • Cerebellar dysplasia in tubulinopathies shows specific features labelled as ‘tubulin-related CD’. • Focal and unilateral involvement of cerebellar hemispheres has important implications for counselling.

BackgroundJoubert syndrome (JS) is an inherited ciliopathy characterized by a complex midbrain–hindbrain malformation and multiorgan involvement. Renal disease, mainly juvenile nephronophthisis (NPH), was reported in 25–30% patients although only ∼18% had a confirmed diagnosis of chronic kidney disease (CKD). NPH often remains asymptomatic for many years, resulting in delayed diagnosis. The aim of the study was to identify a biomarker able to quantify the risk of progressive CKD in young children with JS.MethodsRenal features were investigated in 93 Italian patients, including biochemical tests, ultrasound and 1-deamino-8D-arginine vasopressin test in children with reduced basal urine osmolality. A subset of patients was followed-up over time.ResultsAt last examination, 27 of 93 subjects (29%) presented with CKD, ranging from isolated urinary concentration defect (UCD) to end-stage renal disease. Both normal and pathological urine osmolality levels remained stable over time, even when obtained at very early ages. Follow-up data showed that the probability of developing CKD can be modelled as a function of the urine osmolality value, exceeding 75% for levels ConclusionsWe conclude that the frequency of CKD in JS increases with age and is higher than previously reported. Urine osmolality represents an early sensitive quantitative biomarker of the risk of CKD progression.

BackgroundPontocerebellar hypoplasias (PCH) comprise a group of genetically heterogeneous disorders characterised by concurrent hypoplasia of the pons and the cerebellum and variable clinical and imaging features. The current classification includes 13 subtypes, with ~20 known causative genes. Attempts have been made to delineate the phenotypic spectrum associated to specific PCH genes, yet clinical and neuroradiological features are not consistent across studies, making it difficult to define gene-specific outcomes.MethodsWe performed deep clinical and imaging phenotyping in 56 probands with a neuroradiological diagnosis of PCH, who underwent NGS-based panel sequencing of PCH genes and MLPA for CASK rearrangements. Next, we conducted a phenotype-based unsupervised hierarchical cluster analysis to investigate associations between genes and specific phenotypic clusters.ResultsA genetic diagnosis was obtained in 43 probands (77%). The most common causative gene was CASK, which accounted for nearly half cases (45%) and was mutated in females and occasionally in males. The European founder mutation p.Ala307Ser in TSEN54 and pathogenic variants in EXOSC3 accounted for 18% and 9% of cases, respectively. VLDLR, TOE1 and RARS2 were mutated in single patients. We were able to confirm only few previously reported associations, including jitteriness and clonus with TSEN54 and lower motor neuron signs with EXOSC3. When considering multiple features simultaneously, a clear association with a phenotypic cluster only emerged for EXOSC3.ConclusionCASK represents the major PCH causative gene in Italy. Phenotypic variability associated with the most common genetic causes of PCH is wider than previously thought, with marked overlap between CASK and TSEN54-associated disorders.

Lissencephaly describes a group of conditions characterized by the absence of normal cerebral convolutions and abnormalities of cortical development. To date, at least 20 genes have been identified as involved in the pathogenesis of this condition. Variants in CEP85L, encoding a protein involved in the regulation of neuronal migration, have been recently described as causative of lissencephaly with a posterior-prevalent involvement of the cerebral cortex and an autosomal dominant pattern of inheritance. Here, we describe a 3-year-old boy with slightly delayed psychomotor development and mild dysmorphic features, including bitemporal narrowing, protruding ears with up-lifted lobes and posterior plagiocephaly. Brain MRI at birth identified type 1 lissencephaly, prevalently in the temporo–occipito–parietal regions of both hemispheres with “double-cortex” (Dobyns’ 1–2 degree) periventricular band alterations. Whole-exome sequencing revealed a previously unreported de novo pathogenic variant in the CEP85L gene (NM_001042475.3:c.232+1del). Only 20 patients have been reported as carriers of pathogenic CEP85L variants to date. They show lissencephaly with prevalent posterior involvement, variable cognitive deficits and epilepsy. The present case report indicates the clinical variability associated with CEP85L variants that are not invariantly associated with severe phenotypes and poor outcome, and underscores the importance of including this gene in diagnostic panels for lissencephaly.

Background Ciliopathies are an extensive group of autosomal recessive or X-linked disorders with considerable genetic and clinical overlap, which collectively share multiple organ involvement and may result in lethal or viable phenotypes. In large numbers of cases the genetic defect remains yet to be determined. The aim of this study is to describe the mutational frequency and phenotypic spectrum of the CEP120 gene. Methods Exome sequencing was performed in 145 patients with Joubert syndrome ( JS), including 15 children with oral-facial-digital syndrome type VI (OFDVI) and 21 Meckel syndrome (MKS) fetuses. Moreover, exome sequencing was performed in one fetus with tectocerebellar dysraphia with occipital encephalocele (TCDOE), molar tooth sign and additional skeletal abnormalities. As a parallel study, 346 probands with a phenotype consistent with JS or related ciliopathies underwent next-generation sequencing-based targeted sequencing of 120 previously described and candidate ciliopathy genes. Results We present six probands carrying nine distinct mutations (of which eight are novel) in the CEP120 gene, previously found mutated only in Jeune asphyxiating thoracic dystrophy ( JATD). The CEP120- associated phenotype ranges from mild classical JS in four patients to more severe conditions in two fetuses, with overlapping features of distinct ciliopathies that include TCDOE, MKS, JATD and OFD syndromes. No obvious correlation is evident between the type or location of identified mutations and the ciliopathy phenotype. Conclusion Our findings broaden the spectrum of phenotypes caused by CEP120 mutations that account for nearly 1% of patients with JS as well as for more complex ciliopathy phenotypes. The lack of clear genotype-phenotype correlation highlights the relevance of comprehensive genetic analyses in the diagnostics of ciliopathies.

Early onset cerebellar Ataxia (EOAc) comprises a large group of rare heterogeneous disorders. Determination of the underlying etiology can be difficult given the broad differential diagnosis and the complexity of the genotype-phenotype relationships. This may change the diagnostic work-up into a time-consuming, costly and not always rewarding task. In this overview, the Childhood Ataxia and Cerebellar Group of the European Pediatric Neurology Society (CACG-EPNS) presents a diagnostic algorithm for EOAc patients. In seven consecutive steps, the algorithm leads the clinician through the diagnostic process, including EOA identification, application of the Inventory of Non-Ataxic Signs (INAS), consideration of the family history, neuro-imaging, laboratory investigations, genetic testing by array CGH and Next Generation Sequencing (NGS). In children with EOAc, this algorithm is intended to contribute to the diagnostic process and to allow uniform data entry in EOAc databases. (C) 2019 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.

De novo mutations in the IRF2BPL gene have been identified to date in 18 patients presenting with neuromotor regression, epilepsy and variable neurological signs. Here, we report a female child carrying a novel heterozygous truncating variant in IRF2BPL. Following normal development for two and half years, she developed a progressive neurological condition with psychomotor regression, dystonic tetraparesis with hyperkinetic movements, but no overt epilepsy. Skin biopsy revealed enlarged lysosomes containing granular and tubular material, suggestive of a lysosomal storage disorder. This case expands the IRF2BPL phenotypic spectrum, for the first time providing evidence of endolysosomal storage.

The original version of this article, published on 4 July 2017, unfortunately contained a mistake. The following correction has therefore been made in the original: The first name of the author Raffaella Cusmai was rendered incorrectly and has now been corrected.

Oral-facial-digital type VI syndrome (OFDVI) is a rare phenotype of Joubert syndrome (JS). Recently, C5orf42 was suggested as the major OFDVI gene, being mutated in 9 of 11 families (82 %). We sequenced C5orf42 in 313 JS probands and identified mutations in 28 (8.9 %), most with a phenotype of pure JS. Only 2 out of 17 OFDVI patients (11.7 %) were mutated. A comparison of mutated vs. non-mutated OFDVI patients showed that preaxial and mesoaxial polydactyly, hypothalamic hamartoma and other congenital defects may predict C5orf42 mutations, while tongue hamartomas are more common in negative patients. Electronic supplementary material The online version of this article (doi:10.1007/s00439-014-1508-3) contains supplementary material, which is available to authorized users.

The Sonic Hedgehog (SHH) pathway is a key signaling pathway orchestrating embryonic development, mainly of the CNS and limbs. In vertebrates, SHH signaling is mediated by the primary cilium, and genetic defects affecting either SHH pathway members or ciliary proteins cause a spectrum of developmental disorders. SUFU is the main negative regulator of the SHH pathway and is essential during development. Indeed, Sufu knock-out is lethal in mice, and recessive pathogenic variants of this gene have never been reported in humans. Through whole-exome sequencing in subjects with Joubert syndrome, we identified four children from two unrelated families carrying homozygous missense variants in SUFU. The children presented congenital ataxia and cerebellar vermis hypoplasia with elongated superior cerebellar peduncles (mild “molar tooth sign”), typical cranio-facial dysmorphisms (hypertelorism, depressed nasal bridge, frontal bossing), and postaxial polydactyly. Two siblings also showed polymicrogyria. Molecular dynamics simulation predicted random movements of the mutated residues, with loss of the native enveloping movement of the binding site around its ligand GLI3. Functional studies on cellular models and fibroblasts showed that both variants significantly reduced SUFU stability and its capacity to bind GLI3 and promote its cleavage into the repressor form GLI3R. In turn, this impaired SUFU-mediated repression of the SHH pathway, as shown by altered expression levels of several target genes. We demonstrate that germline hypomorphic variants of SUFU cause deregulation of SHH signaling, resulting in recessive developmental defects of the CNS and limbs which share features with both SHH-related disorders and ciliopathies.

Item does not contain fulltext The neuron-restricted isoform 3 of the plasma membrane Ca(2+) ATPase plays a major role in the regulation of Ca(2+) homeostasis in the brain, where the precise control of Ca(2+) signaling is a necessity. Several function-affecting genetic mutations in the PMCA3 pump associated to X-linked congenital cerebellar ataxias have indeed been described. Interestingly, the presence of co-occurring mutations in additional genes suggest their synergistic action in generating the neurological phenotype as digenic modulators of the role of PMCA3 in the pathologies. Here we report a novel PMCA3 mutation (G733R substitution) in the catalytic P-domain of the pump in a patient affected by non-progressive ataxia, muscular hypotonia, dysmetria and nystagmus. Biochemical studies of the pump have revealed impaired ability to control cellular Ca(2+) handling both under basal and under stimulated conditions. A combined analysis by homology modeling and molecular dynamics have revealed a role for the mutated residue in maintaining the correct 3D configuration of the local structure of the pump. Mutation analysis in the patient has revealed two additional function-impairing compound heterozygous missense mutations (R123Q and G214S substitution) in phosphomannomutase 2 (PMM2), a protein that catalyzes the isomerization of mannose 6-phosphate to mannose 1-phosphate. These mutations are known to be associated with Type Ia congenital disorder of glycosylation (PMM2-CDG), the most common group of disorders of N-glycosylation. The findings highlight the association of PMCA3 mutations to cerebellar ataxia and strengthen the possibility that PMCAs act as digenic modulators in Ca(2+)-linked pathologies.

Dysequilibrium syndrome (DES) is a non-progressive congenital ataxia characterized by severe intellectual deficit, truncal ataxia and markedly delayed, quadrupedal or absent ambulation. Recessive loss-of-function mutations in the very low density lipoprotein receptor (VLDLR) gene represent the most common cause of DES. Only two families have been reported harbouring homozygous missense mutations, both with a similarly severe phenotype. We report an Italian girl with very mild DES caused by the novel homozygous VLDLR missense mutation p.(C419Y). This unusually benign phenotype possibly relates to a less disruptive effect of the mutation, falling within a domain (EGF-B) not predicted as crucial for the protein function.

Cerebellar dysplasia with cysts and abnormal shape of the fourth ventricle, in the absence of significant supratentorial anomalies and of muscular involvement, defines recessively inherited Poretti-Boltshauser syndrome (PBS). Clinical features comprise non-progressive cerebellar ataxia, intellectual disability of variable degree, language impairment, ocular motor apraxia and frequent occurrence of myopia or retinopathy. Recently, loss-of-function variants in the LAMA1 gene were identified in six probands with PBS. Here we report the detailed clinical, neuroimaging and genetic characterization of 18 PBS patients from 15 unrelated families. Biallelic LAMA1 variants were identified in 14 families (93%). The only non-mutated proband presented atypical clinical and neuroimaging features, challenging the diagnosis of PBS. Sixteen distinct variants were identified, which were all novel. In particular, the frameshift variant c.[2935delA] recurred in six unrelated families on a shared haplotype, suggesting a founder effect. No LAMA1 variants could be detected in 27 probands with different cerebellar dysplasias or non-progressive cerebellar ataxia, confirming the strong correlate between LAMA1 variants and PBS.

Aim of this study is to show the potential of probabilistic tractographic techniques, based on the Constrained Spherical Deconvolution (CSD) algorithms, in recognizing white matter fiber bundle anomalies in patients with complex cerebral malformations, such as cerebellar agenesis. The morphological and tractographic study of a 17-year-old male patient affected by cerebellar agenesis was performed by using a 3Tesla MRI scanner. Genetic and neuropsychological tests were carried out. An MRI morphological study showed the absence of both cerebellar hemispheres and the flattening of the anterior side of the pons. Moreover, it showed a severe vermian hypoplasia with a minimal vermian residual. The study recognized two thin cerebellar remnants, medially in contact with the small vermian residual, at the pontine level. The third ventricle, morphologically normal, communicated with a permagna cerebello-medullary cistern. Probabilistic CSD tractography identified some abnormal and aberrant infratentorial tracts, symmetrical on both sides. In particular, the transverse pontine fibers were absent and the following tracts with aberrant trajectories have been identified: “cerebello-thalamic” tracts; “fronto-cerebellar” tracts; and ipsilateral and contralateral “spino-cerebellar” tracts. Abnormal tracts connecting the two thin cerebellar remnants have also been detected. There were no visible alterations in the main supratentorial tracts in either side. Neuropsychiatric evaluation showed moderate cognitive-motor impairment with discrete adaptive compensation. Probabilistic CSD tractography is a promising technique that overcome reconstruction biases of other diffusion tensor-based approaches and allowed us to recognize, in a patient with cerebellar agenesis, abnormal tracts and aberrant trajectories of normally existing tracts.

Background and purpose Mutations in the PLA2G6 gene are causative of PLA2G6-associated neurodegeneration (PLAN), a spectrum of neurodegenerative conditions including infantile, childhood and adult onset forms. Methods Seventeen North African patients with a clinical suspicion of infantile-onset PLAN underwent clinical, neurophysiological and neuroimaging examinations, and PLA2G6 sequencing. Haplotype analysis was performed to date the identified founder mutation. Results All patients carried biallelic mutations in PLA2G6. Sixteen children had the commonest form of infantile-onset PLAN, with early onset of psychomotor regression, hypotonia, pyramidal and cerebellar signs, and abnormal ocular movements. The phenotype was highly homogeneous, with rapid development of severe spastic tetraparesis, cognitive impairment and optic atrophy. Neuroimaging showed cerebellar atrophy and claval hypertrophy to be the commonest and earliest signs, whilst cerebellar cortex hyperintensity and pallidal iron deposition were later findings. Motor or sensory-motor neuropathy and electroencephalogram fast rhythms were also frequent. Nine patients from six families shared the same founder mutation (p.V691del) which probably arose by the late seventeenth century. Only one patient fitted the diagnosis of the much rarer childhood-onset PLAN. Despite the early onset (18 months), clinical progression was slower, with behavioral disturbances and dystonia. Typical features of infantile-onset PLAN such as hypotonia, nystagmus/strabismus, optic atrophy, electroencephalogram fast rhythms and motor neuropathy were absent. Cerebellar atrophy, claval hypertrophy and pallidal hypointensity were evident at brain magnetic resonance imaging. This patient carried a missense variant predicted to be less deleterious. Conclusions The PLAN-associated phenotypes and the challenges of diagnosing the childhood-onset form are delineated, and a common North African founder mutation is identifed.

Joubert syndrome (JS) is an autosomal recessive or X-linked congenital cerebellar ataxia characterised by a peculiar hindbrain–midbrain malformation, the ‘molar tooth sign’ (MTS). JS is characterised by neonatal hypotonia which later evolves into ataxia, developmental delay, abnormal eye movements, breathing abnormalities and intellectual disability. This neurological presentation can be variably complicated by the involvement of multiple organs such as the kidneys, retina, liver and skeleton. JS is genetically heterogeneous, with 26 causative genes identified to date. All genes encode for proteins of the primary cilium, a nearly ubiquitous subcellular organelle that plays essential roles in embryonic development and cell functioning. Indeed, JS is part of ciliopathies, an expanding group of disorders that share many clinical and genetic determinants. The marked clinical and genetic heterogeneity of JS and ciliopathies may be explained by oligogenic inheritance and the existence of genetic modifiers. Key Concepts: Joubert syndrome (JS) is a congenital ataxia with autosomal or X-linked recessive inheritance. The diagnostic hallmark of JS is a peculiar cerebellar and brainstem malformation, the so-called ‘molar tooth sign’ recognisable on brain imaging. Neurological features of JS include hypotonia, ataxia, developmental delay, intellectual impairment, oculomotor abnormalities and alterations of the breathing pattern in neonatal age. JS may present with variable involvement of the eyes, kidneys, liver, polydactyly and oral-facial defects. JS is genetically heterogeneous, with 26 genes identified to date, that are overall responsible of about half cases. JS pathogenesis is related to the dysfunction of the primary cilium, making JS part of the expanding group of ‘ciliopathies’. The primary cilium is an immotile organelle, located of the surface of nearly every cell type, that plays key roles in cellular functioning and embryonic development. Ciliopathies are characterised by wide clinical and genetic heterogeneity, and present significant clinical and genetic overlap among distinct conditions. Such complexity has been partly explained by showing oligogenic inheritance and the existence of genetic modifiers of the phenotype. Keywords: Joubert syndrome; Meckel syndrome; primary cilium; cerebellum; cerebellar hypoplasia; ciliopathies; cerebellar ataxia; molar tooth sign; oligogenic inheritance

Joubert syndrome is a clinically and genetically heterogeneous ciliopathy characterized by a typical cerebellar and brainstem malformation (the “molar tooth sign”), and variable multiorgan involvement. To date, 24 genes have been found mutated in Joubert syndrome, of which 13 also cause Meckel syndrome, a lethal ciliopathy with kidney, liver and skeletal involvement. Here we describe four patients with mild Joubert phenotypes who carry pathogenic mutations in either MKS1 or B9D1, two genes previously implicated only in Meckel syndrome.

International audience; Joubert syndrome (JS) is characterized by a distinctive cerebellar structural defect, namely the << molar tooth sign >>. JS is genetically heterogeneous, involving 20 genes identified to date, which are all required for cilia biogenesis and/or function. In a consanguineous family with JS associated with optic nerve coloboma, kidney hypoplasia, and polydactyly, combined exome sequencing and mapping identified a homozygous splice-site mutation in PDE6D, encoding a prenyl-binding protein. We found that pde6d depletion in zebrafish leads to renal and retinal developmental anomalies and wild-type but not mutant PDE6D is able to rescue this phenotype. Proteomic analysis identified INPP5E, whose mutations also lead to JS or mental retardation, obesity, congenital retinal dystrophy, and micropenis syndromes, as novel prenyl-dependent cargo of PDE6D. Mutant PDE6D shows reduced binding to INPP5E, which fails to localize to primary cilia in patient fibroblasts and tissues. Furthermore, mutant PDE6D is unable to bind to GTP-bound ARL3, which acts as a cargo-release factor for PDE6D-bound INPP5E. Altogether, these results indicate that PDE6D is required for INPP5E ciliary targeting and suggest a broader role for PDE6D in targeting other prenylated proteins to the cilia. This study identifies PDE6D as a novel JS disease gene and provides the first evidence of prenyl-binding-dependent trafficking in ciliopathies.

Summary Joubert syndrome is a congenital cerebellar ataxia with autosomal recessive or X-linked inheritance, the diagnostic hallmark of which is a unique cerebellar and brainstem malformation recognisable on brain imaging—the so-called molar tooth sign. Neurological signs are present from the neonatal period and include hypotonia progressing to ataxia, global developmental delay, ocular motor apraxia, and breathing dysregulation. These signs are variably associated with multiorgan involvement, mainly of the retina, kidneys, skeleton, and liver. 21 causative genes have been identified so far, all of which encode for proteins of the primary cilium or its apparatus. The primary cilium is a subcellular organelle that has key roles in development and in many cellular functions, making Joubert syndrome part of the expanding family of ciliopathies. Notable clinical and genetic overlap exists between distinct ciliopathies, which can co-occur even within families. Such variability is probably explained by an oligogenic model of inheritance, in which the interplay of mutations, rare variants, and polymorphisms at distinct loci modulate the expressivity of the ciliary phenotype.