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To obtain novel candidate genes for autosomal dominant spinocerebellar ataxia and other neurodegenerative disorders in which gene mutations remain unidentified, we screened a human fetal brain cDNA library using (CAG)[sub 10] repeat probes. Sixteen cDNAs were isolated and mapped to chromosomes 1, 2, 3, 6, 9, 13, 15, 16, 22, and X. Although we failed to detect abnormal CAG repeat expansion within these genes in Japanese patients with inherited neurodegenerative diseases, these genes remain potential candidate genes for neurodegenerative diseases that feature anticipation. [ABSTRACT FROM AUTHOR]

Loss-of-function (LoF) variants in NEK1 have recently been reported to be associated with amyotrophic lateral sclerosis (ALS). In this study, we investigated the association of NEK1 LoF variants with an increased risk of sporadic ALS (SALS) and the clinical characteristics of patients with SALS carrying LoF variants in a Japanese case series. Whole-exome sequencing analysis was performed for a series of 446 SALS patients in whom pathogenic variants in familial ALS-causative genes have not been identified and 1163 healthy control subjects in our Japanese series. We evaluated LoF variants, defined as nonsense, splice-site disrupting single-nucleotide variants (SNVs), or short insertion/deletion (indel) variants predicted to cause frameshifts in NEK1. We identified seven NEK1 LoF variants in patients with SALS (1.57%), whereas only one was identified in control subjects (0.086%) (P = 0.00073, Fisher's exact test). This finding is consistent with those in recent reports from other regions in the world. In conclusion, we demonstrated that NEK1 LoF variants are also associated with an increased risk of SALS in the Japanese population.

Hereditary spastic paraplegia (HSP) is one of the most genetically heterogeneous neurodegenerative disorders characterized by progressive spasticity and pyramidal weakness of lower limbs. Because >30 causative genes have been identified, screening of multiple genes is required for establishing molecular diagnosis of individual patients with HSP. To elucidate molecular epidemiology of HSP in the Japanese population, we have conducted mutational analyses of 16 causative genes of HSP (L1CAM, PLP1, ATL1, SPAST, CYP7B1, NIPA1, SPG7, KIAA0196, KIF5A, HSPD1, BSCL2, SPG11, SPG20, SPG21, REEP1 and ZFYVE27) using resequencing microarrays, array-based comparative genomic hybridization and Sanger sequencing. The mutational analysis of 129 Japanese patients revealed 49 mutations in 46 patients, 32 of which were novel. Molecular diagnosis was accomplished for 67.3% (33/49) of autosomal dominant HSP patients. Even among sporadic HSP patients, mutations were identified in 11.1% (7/63) of them. The present study elucidated the molecular epidemiology of HSP in the Japanese population and further broadened the mutational and clinical spectra of HSP.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by neurodegeneration, most notably of dopaminergic neurons in the substantia nigra. To date, six causative genes have been identified including LRRK2, whose mutations are the most frequent in autosomal dominant PD (Ad-PD). We conducted a comprehensive mutational analysis of LRRK2 in 30 Ad-PD (11 Japanese and 19 Caucasian) families employing a DNA microarray-based resequencing system and direct nucleotide sequence analysis, and identified 23 variants including two known mutations, p.G2019S and p.I1371V, in three Caucasian families and one Caucasian family, respectively, a novel putative pathogenic mutation, p.N1221K, in one Japanese family, and a known nonsynonymous variant, p.G2385R, in two Japanese families. Detailed analysis of the frequency of p.G2385R among 100 Japanese Ad-PD, 73 sporadic PD (sPD) and 238 controls revealed that the frequency of the p.G2385R variant was significantly higher in Ad-PD than in controls (allele frequency, 9.0 vs 2.1%) (χ(2)=16.32, P=5.34 × 10(-5)). The p.G2385R variant, however, did not show complete cosegregation with PD. In addition, the frequency of p.G2385R was also higher in sPD than in controls, although not significant (allele frequency, 3.4 vs 2.1%) (χ(2)=0.76, P=0.38). These observations support the possibility that p.G2385R is associated with an increased risk of PD.

We have recently found that multiple rare variants of the glucocerebrosidase gene (GBA) confer a robust risk for Parkinson disease, supporting the 'common disease-multiple rare variants' hypothesis. To develop an efficient method of identifying rare variants in a large number of samples, we applied multiplexed resequencing using a next-generation sequencer to identification of rare variants of GBA. Sixteen sets of pooled DNAs from six pooled DNA samples were prepared. Each set of pooled DNAs was subjected to polymerase chain reaction to amplify the target gene (GBA) covering 6.5 kb, pooled into one tube with barcode indexing, and then subjected to extensive sequence analysis using the SOLiD System. Individual samples were also subjected to direct nucleotide sequence analysis. With the optimization of data processing, we were able to extract all the variants from 96 samples with acceptable rates of false-positive single-nucleotide variants.