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Mutations in proline-rich transmembrane protein 2 (PRRT2) cause paroxysmal kinesigenic dyskinesia (PKD). Recently, we reported that a Prrt2 mutation exacerbated L-dopa-induced motor deficits in mice, suggesting that the basal ganglia might contribute to PKD pathology. Here, we demonstrated that the Prrt2 mutation enhanced depolarization stimuli-induced extracellular dopamine levels in the mouse striatum, which were attenuated by repeated stimulation. L-dopa administration maintained high dopamine levels in Prrt2-KI mice even during repetitive stimuli but did not affect dopamine levels in wild-type mice. Thus, the enhanced and prolonged responsiveness of dopamine release in nigrostriatal dopaminergic neurons to sequential excitation may be partially implicated in Prrt2-related dyskinesia., (© 2024 The Author(s). Neuropsychopharmacology Reports published by John Wiley & Sons Australia, Ltd on behalf of The Japanese Society of Neuropsychopharmacology.)

Mutations of proline-rich transmembrane protein 2 (PRRT2) lead to dyskinetic disorders such as paroxysmal kinesigenic dyskinesia (PKD), which is characterized by attacks of involuntary movements precipitated by suddenly initiated motion, and some convulsive disorders. Although previous studies have shown that PKD might be caused by cerebellar dysfunction, PRRT2 has not been sufficiently analyzed in some motor-related regions, including the basal ganglia, where dopaminergic neurons are most abundant in the brain. Here, we generated several types of Prrt2 knock-in (KI) mice harboring mutations, such as c.672dupG, that mimics the human pathological mutation c.649dupC and investigated the contribution of Prrt2 to dopaminergic regulation. Regardless of differences in the frameshift sites, all truncating mutations abolished Prrt2 expression within the striatum and cerebral cortex, consistent with previous reports of similar Prrt2 mutant rodents, confirming the loss-of-function nature of these mutations. Importantly, administration of l-dopa, a precursor of dopamine, exacerbated rotarod performance, especially in Prrt2-KI mice. These findings suggest that dopaminergic dysfunction in the brain by the PRRT2 mutation might be implicated in a part of motor symptoms of PKD and related disorders., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.)

Genetic and epidemiological evidence has suggested that genetic factors are important in schizophrenia, although its pathophysiology is poorly understood. This study used whole-exome sequencing to investigate potential novel schizophrenia-causing genes in a Japanese family containing several members affected by severe or treatment-resistant schizophrenia. A missense variant, chr12:132064747C>T (rs200626129, P2805L), in the E1A-binding protein P400 (EP400) gene completely segregated with schizophrenia in this family. Furthermore, numerous other EP400 mutations were identified in the targeted sequencing of a schizophrenia patient cohort. We also created two lines of Ep400 gene-edited mice, which had anxiety-like behaviours and reduced axon diameters. Our findings suggest that rs200626129 in EP400 is likely to cause schizophrenia in this Japanese family, and may lead to a better understanding and treatment of schizophrenia.

Panic disorder (PD) is a common and debilitating neuropsychiatric disorder characterized by panic attacks coupled with excessive anxiety. Both genetic factors and environmental factors play an important role in PD pathogenesis and response to treatment. However, PD is clinically heterogeneous and genetically complex, and the exact genetic or environmental causes of this disorder remain unclear. Various approaches for detecting disease-causing genes have recently been made available. In particular, genome-wide association studies (GWAS) have attracted attention for the identification of disease-associated loci of multifactorial disorders. This review introduces GWAS of PD, followed by a discussion about the limitations of GWAS and the major challenges facing geneticists in the post-GWAS era. Alternative strategies to address these challenges are then proposed, such as epigenome-wide association studies (EWAS) and rare variant association studies (RVAS) using next-generation sequencing. To date, however, few reports have described these analyses, and the evidence remains insufficient to confidently identify or exclude rare variants or epigenetic changes in PD. Further analyses are therefore required, using sample sizes in the tens of thousands, extensive functional annotations, and highly targeted hypothesis testing.

Twin studies of psychiatric disorders such as schizophrenia and autism spectrum disorder have employed epidemiological approaches that determine heritability by comparing the concordance rate between monozygotic twins (MZs) and dizygotic twins. The basis for these studies is that MZs share 100% of their genetic information. Recently, biological studies based on molecular methods are now being increasingly applied to examine the differences between MZs discordance for psychiatric disorders to unravel their possible causes. Although recent advances in next-generation sequencing have increased the accuracy of this line of research, there has been greater emphasis placed on epigenetic changes versus DNA sequence changes as the probable cause of discordant psychiatric disorders in MZs. Since the epigenetic status differs in each tissue type, in addition to the DNA from the peripheral blood, studies using DNA from nerve cells induced from postmortem brains or induced pluripotent stem cells are being carried out. Although it was originally thought that epigenetic changes occurred as a result of environmental factors, and thus were not transmittable, it is now known that such changes might possibly be transmitted between generations. Therefore, the potential possible effects of intestinal flora inside the body are currently being investigated as a cause of discordance in MZs. As a result, twin studies of psychiatric disorders are greatly contributing to the elucidation of genetic and environmental factors in the etiology of psychiatric conditions.

Mutations of PRRT2 (proline-rich transmembrane protein 2) cause several neurological disorders, represented by paroxysmal kinesigenic dyskinesia (PKD), which is characterized by attacks of involuntary movements triggered by sudden voluntary movements. PRRT2 is reported to suppress neuronal excitation, but it is unclear how the function of PRRT2 is modulated during neuronal excitation. We found that PRRT2 is processed to a 12 kDa carboxy-terminal fragment (12K-CTF) by calpain, a calcium-activated cysteine protease, in a neuronal activity-dependent manner, predominantly via NMDA receptors or voltage-gated calcium channels. Furthermore, we clarified that 12K-CTF is generated by sequential cleavages at Q220 and S244. The amino-terminal fragment (NTF) of PRRT2, which corresponds to PKD-related truncated mutants, is not detected, probably due to rapid cleavage at multiple positions. Given that 12K-CTF lacks most of the proline-rich domain, this cleavage might be involved in the activity-dependent enhancement of neuronal excitation perhaps through transient retraction of PRRT2's function. Therefore, PRRT2 might serve as a buffer for neuronal excitation, and lack of this function in PKD patients might cause neuronal hyperexcitability in their motor circuits., (© 2019 Federation of American Societies for Experimental Biology.)

Objective: To identify genes related to normal-pressure hydrocephalus (NPH) in one Japanese family with several members with NPH., Methods: We performed whole-exome sequencing (WES) on a Japanese family with multiple individuals with NPH and identified a candidate gene. Then we generated knockout mouse using CRISPR/Cas9 to confirm the effect of the candidate gene on the pathogenesis of hydrocephalus., Results: In WES, we identified a loss-of-function variant in CFAP43 that segregated with the disease. CFAP43 encoding cilia- and flagella-associated protein is preferentially expressed in the testis. Recent studies have revealed that mutations in this gene cause male infertility owing to morphologic abnormalities of sperm flagella. We knocked out mouse ortholog Cfap43 using CRISPR/Cas9 technology, resulting in Cfap43 -deficient mice that exhibited a hydrocephalus phenotype with morphologic abnormality of motile cilia., Conclusion: Our results strongly suggest that CFAP43 is responsible for morphologic or movement abnormalities of cilia in the brain that result in NPH., (Copyright © 2019 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)

Panic disorder (PD) is characterized by recurrent and unexpected panic attacks, subsequent anticipatory anxiety, and phobic avoidance. Recent epidemiological and genetic studies have revealed that genetic factors contribute to the pathogenesis of PD. We performed whole-exome sequencing on one Japanese family, including multiple patients with panic disorder, which identified seven rare protein-altering variants. We then screened these genes in a Japanese PD case-control group (384 sporadic PD patients and 571 controls), resulting in the detection of three novel single nucleotide variants as potential candidates for PD (chr15: 42631993, T>C in GANC; chr15: 42342861, G>T in PLA2G4E; chr20: 3641457, G>C in GFRA4). Statistical analyses of these three genes showed that PLA2G4E yielded the lowest p value in gene-based rare variant association tests by Efficient and Parallelizable Association Container Toolbox algorithms; however, the p value did not reach the significance threshold in the Japanese. Likewise, in a German case-control study (96 sporadic PD patients and 96 controls), PLA2G4E showed the lowest p value but again did not reach the significance threshold. In conclusion, we failed to find any significant variants or genes responsible for the development of PD. Nonetheless, our results still leave open the possibility that rare protein-altering variants in PLA2G4E contribute to the risk of PD, considering the function of this gene.

Monozygotic (MZ) twins have been thought to be genetically identical. However, recent studies have shown discordant variants between them. We performed whole-exome sequencing (WES) in five MZ twin pairs with discordant neurodevelopmental disorders and one healthy control MZ twin to detect discordant variants. We identified three discordant variants confirmed by deep sequencing after analysis by personalized next-generation sequencing (NGS). Three mutations in FBXO38 (chr5:147774428;T>G), SMOC2 (chr6:169051385;A>G) and TDRP (chr8:442616;A>G), were detected with low allele frequency of mutant alleles on deep sequencing, suggesting that these loci are mosaic due to somatic mutations in a developmental stage. Our results suggest that deep sequencing analysis would be an adequate method to detect discordant mutations in candidate genes responsible for heritable diseases., Competing Interests: The authors declare no conflict of interest.

Here we report de novo non-synonymous single-nucleotide variants (SNVs) by conducting whole exome sequencing of 18 trios consisting of Japanese patients with sporadic schizophrenia and their parents. Among nine SNVs, we explored the functional impact of the de novo mutation in TBL1XR1 [c.30 C > G (p.Phe10Leu)], a gene previously found to be associated with autism spectrum disorder and epilepsy. Protein structural analysis revealed that Phe10Leu mutation may decrease the structural stability of the TBL1XR1 protein. We demonstrate that Phe10Leu mutation alters the interaction of TBL1XR1 with N-CoR and β-catenin, which play critical roles in regulation of Wnt-mediated transcriptional activity. Consistently, TBL1XR1-mediated activation of Wnt signaling was up-regulated by Phe10Leu mutation. These results suggest that a de novo TBL1XR1 point mutation could alter Wnt/β-catenin signaling activity. Further studies are required to clarify the involvement of TBL1XR1 mutations in neuropsychiatric conditions.

Paroxysmal kinesigenic dyskinesia (PKD (MIM128000)) is a neurological disorder characterized by recurrent attacks of involuntary movements. Benign familial infantile convulsion (BFIC) is also one of a neurological disorder characterized by clusters of epileptic seizures. The BFIC1 (MIM601764), BFIC2 (MIM605751) and BFIC4 (MIM612627) loci have been mapped to chromosome 19q, 16p and 1p, respectively, while BFIC3 (MIM607745) is caused by mutations in SCN2A on chromosome 2q24. Furthermore, patients with BFIC have been observed in a family concurrently with PKD. Both PKD and BFIC2 are heritable paroxysmal disorders and map to the same region on chromosome 16. Recently, the causative gene of PKD, the protein-rich transmembrane protein 2 (PRRT2), has been detected using whole-exome sequencing. We performed mutation analysis of PRRT2 by direct sequencing in 81 members of 17 families containing 15 PKD families and two BFIC families. Direct sequencing revealed that two mutations, c.649dupC and c.748C>T, were detected in all members of the PKD and BFIC families. Our results suggest that BFIC2 is caused by a truncated mutation that also causes PKD. Thus, PKD and BFIC2 are genetically identical and may cause convulsions and involuntary movements via a similar mechanism.

Sotos syndrome is characterized by prenatal and postnatal overgrowth, characteristic craniofacial features and mental retardation. Haploinsufficiency of NSD1 causes Sotos syndrome. Recently, two microdeletions encompassing Nuclear Factor I-X (NFIX) and a nonsense mutation in NFIX have been found in three individuals with Sotos-like overgrowth features, suggesting possible involvements of NFIX abnormalities in Sotos-like features. Interestingly, seven frameshift and two splice site mutations in NFIX have also been found in nine individuals with Marshall-Smith syndrome. In this study, 48 individuals who were suspected as Sotos syndrome but showing no NSD1 abnormalities were examined for NFIX mutations by high-resolution melt analysis. We identified two heterozygous missense mutations in the DNA-binding/dimerization domain of the NFIX protein. Both mutations occurred at evolutionally conserved amino acids. The c.179T>C (p.Leu60Pro) mutation occurred de novo and the c.362G>C (p.Arg121Pro) mutation was inherited from possibly affected mother. Both mutations were absent in 250 healthy Japanese controls. Our study revealed that missense mutations in NFIX were able to cause Sotos-like features. Mutations in DNA-binding/dimerization domain of NFIX protein also suggest that the transcriptional regulation is abnormally fluctuated because of NFIX abnormalities. In individuals with Sotos-like features unrelated to NSD1 changes, genetic testing of NFIX should be considered.

The recent development of high-resolution DNA microarrays, in which hundreds of thousands of single nucleotide polymorphisms (SNPs) are genotyped, enables the rapid identification of susceptibility genes for complex diseases. Clusters of these SNPs may show runs of homozygosity (ROHs) that can be analyzed for association with disease. An analysis of patients whose parents were first cousins enables the search for autozygous segments in their offspring. Here, using the Affymetrix® Genome-Wide Human SNP Array 5.0 to determine ROHs, we genotyped 9 individuals with schizophrenia (SCZ) whose parents were first cousins. We identified overlapping ROHs on chromosomes 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 16, 17, 19, 20, and 21 in at least 3 individuals. Only the locus on chromosome 5 has been reported previously. The ROHs on chromosome 5q23.3-q31.1 include the candidate genes histidine triad nucleotide binding protein 1 (HINT1) and acyl-CoA synthetase long-chain family member 6 (ACSL6). Other overlapping ROHs may contain novel rare recessive variants that affect SCZ specifically in our samples, given the highly heterozygous nature of SCZ. Analysis of patients whose parents are first cousins may provide new insights for the genetic analysis of psychiatric diseases.

Copy number variations (CNVs) are common structural variations in the human genome that strongly affect genomic diversity and can play a role in the development of several diseases, including neurodevelopmental disorders. Recent reports indicate that monozygotic twins can show differential CNV profiles. We searched CNVs in monozygotic twins discordant for schizophrenia to identify susceptible loci for schizophrenia. Three pairs of monozygotic twins discordant for schizophrenia were subjected to analysis. Genomic DNA samples were extracted from peripheral blood lymphocytes. We adopted the Affymetrix Genome-Wide Human SNP (Single Nucleotide Polymorphism) Array 6.0 to detect copy number discordance using Partek Genomics Suite 6.5 beta. In three twin pairs, however, validations by quantitative PCR and DNA sequencing revealed that none of the regions had any discordance between the three twin pairs. Our results support the hypothesis that epigenetic changes or fluctuation in developmental process triggered by environmental factors mainly contribute to the pathogenesis of schizophrenia. Schizophrenia caused by strong genetics factors including copy number alteration or gene mutation may be a small subset of the clinical population.

Sotos syndrome is a well-known anomaly syndrome characterized by overgrowth, characteristic facial gestalt, and developmental delay, and haploinsufficiency of the NSD1 gene has been revealed as one of the major genetic causes. However, there have been only a few reports on neuroradiologic findings by computed tomography (CT) or magnetic resonance imaging (MRI), and functional examination of the brain has not been reported. We examined three cases with typical Sotos syndrome, which also were confirmed by genetic analysis with a specific probe for the NSD1 gene. The results of MRI showed the characteristic features that have been reported previously. The findings obtained by using single-photon emission computed tomography and magnetic resonance spectroscopy suggested an association between mental delay and behavioral tendency in Sotos syndrome and immaturity in frontal brain function.

Purpose: We tested the hypothesis that Sotos syndrome (SoS) due to the common deletion is a contiguous gene syndrome incorporating plasma coagulation factor twelve (FXII) deficiency. The relationship between FXII activity and the genotype at a functional polymorphism of the FXII gene was investigated., Methods: A total of 21 patients including those with the common deletion, smaller deletions, and point mutations, and four control individuals were analyzed. We examined FXII activity in patients and controls, and analyzed their FXII 46C/T genotype using direct DNA sequencing., Results: Among 10 common deletion patients, seven patients had lower FXII activity with the 46T allele of the FXII gene, whereas three patients had normal FXII activity with the 46C allele. Two patients with smaller deletions, whose FXII gene is not deleted had low FXII activity, but one patient with a smaller deletion had normal FXII. Four point mutation patients and controls all had FXII activities within the normal range., Conclusion: FXII activity in SoS patients with the common deletion is predominantly determined by the functional polymorphism of the remaining hemizygous FXII allele. Thus, Sotos syndrome is a contiguous gene syndrome incorporating coagulation factor twelve (FXII) deficiency.

Sotos syndrome (Sos) is an overgrowth disorder also characterized clinically by mental retardation, specific craniofacial features and advanced bone age. As NSD1 haploinsufficiency was determined in 2002 to be the major cause of Sos, many intragenic mutations and chromosomal microdeletions involving the entire NSD1 gene have been described. In the Japanese population, half of the cases analyzed appear to have a common microdeletion; however, in the European population, deletion cases account for only 9%. Blast analysis of the Sos genomic region on 5q35 revealed two complex mosaic low-copy repeats (LCRs) that are centromeric and telomeric to NSD1. We termed these proximal Sos-REP (Sos-PREP, approximately 390 kb) and distal Sos-REP (Sos-DREP, approximately 429 kb), respectively. On the basis of the analysis of DNA sequence, we determined the size, structure, orientation and extent of sequence identity of these LCRs. We found that Sos-PREP and Sos-DREP are composed of six subunits termed A-F. Each of the homologous subunits, with the exception of one, is located in an inverted orientation and the order of subunits is different between the two Sos-REPs. Only the subunit C' in Sos-DREP is oriented directly with respect to the subunit C in Sos-PREP. These latter C' and C subunits are greater than 99% identical. Using pulsed-field gel electrophoresis analysis in eight Sos patients with a common deletion, we detected an approximately 550 kb junction fragment that we predicted according to the non-allelic homologous recombination (NAHR) mechanism using directly oriented Sos-PREP C and Sos-DREP C' subunits as substrates. This patient specific junction fragment was not present in 51 Japanese and non-Japanese controls. Subsequently, using long-range PCR with restriction enzyme digestion and DNA sequencing, we identified a 2.5 kb unequal crossover hotspot region in six out of nine analyzed Sos patients with the common deletion. Our data are consistent with an NAHR mechanism for generation of the Sos common deletion.

Sotos syndrome (SoS) is an autosomal dominant overgrowth syndrome with characteristic craniofacial dysmorphic features and various degrees of mental retardation. We previously showed that haploinsufficiency of the NSD1 gene is the major cause of SoS, and submicroscopic deletions at 5q35, including NSD1, were found in about a half (20/42) of our patients examined. Since the first report, an additional 70 SoS cases consisting of 53 Japanese and 17 non-Japanese have been analyzed. We found 50 microdeletions (45%) and 16 point mutations (14%) among all the 112 cases. A large difference in the frequency of microdeletions between Japanese and non-Japanese patients was noted: 49 (52%) of the 95 Japanese patients and only one (6%) of the 17 non-Japanese had microdeletions. A sequence-based physical map was constructed to characterize the microdeletions. Most of the microdeletions were confirmed to be identical by FISH analysis. We identified highly homologous sequences, i.e., possible low copy repeats (LCRs), in regions flanking proximal and distal breakpoints of the common deletion, This suggests that LCRs may mediate the deletion. Such LCRs seem to be present in different populations. Thus the different frequency of microdeletions between Japanese and non-Japanese cases in our study may have been caused by patient-selection bias., (Copyright 2003 Wiley-Liss, Inc.)

Sotos syndrome (SoS) is characterized by pre- and postnatal overgrowth with advanced bone age; a dysmorphic face with macrocephaly and pointed chin; large hands and feet; mental retardation; and possible susceptibility to tumors. It has been shown that the major cause of SoS is haploinsufficiency of the NSD1 gene at 5q35, because the majority of patients had either a common microdeletion including NSD1 or a truncated type of point mutation in NSD1. In the present study, we traced the parental origin of the microdeletions in 26 patients with SoS by the use of 16 microsatellite markers at or flanking the commonly deleted region. Deletions in 18 of the 20 informative cases occurred in the paternally derived chromosome 5, whereas those in the maternally derived chromosome were found in only two cases. Haplotyping analysis of the marker loci revealed that the paternal deletion in five of seven informative cases and the maternal deletion in one case arose through an intrachromosomal rearrangement, and two other cases of the paternal deletion involved an interchromosomal event, suggesting that the common microdeletion observed in SoS did not occur through a uniform mechanism but preferentially arose prezygotically.

We isolated NSD1 from the 5q35 breakpoint in an individual with Sotos syndrome harboring a chromosomal translocation. We identified 1 nonsense, 3 frameshift and 20 submicroscopic deletion mutations of NSD1 among 42 individuals with sporadic cases of Sotos syndrome. The results indicate that haploinsufficiency of NSD1 is the major cause of Sotos syndrome.