Recent studies have established important roles of de novo mutations (DNMs) in autism spectrum disorders (ASDs). Here, we analyze DNMs in 262 ASD probands of Japanese origin and confirm the "de novo paradigm" of ASDs across ethnicities. Based on this consistency, we combine the lists of damaging DNMs in our and published ASD cohorts (total number of trios, 4,244) and perform integrative bioinformatics analyses. Besides replicating the findings of previous studies, our analyses highlight ATP-binding genes and fetal cerebellar/striatal circuits. Analysis of individual genes identified 61 genes enriched for damaging DNMs, including ten genes for which our dataset now contributes to statistical significance. Screening of compounds altering the expression of genes hit by damaging DNMs reveals a global downregulating effect of valproic acid, a known risk factor for ASDs, whereas cardiac glycosides upregulate these genes. Collectively, our integrative approach provides deeper biological and potential medical insights into ASDs.

Ankyrin-G, a modular protein, plays a critical role in clustering voltage-gated sodium channels (Nav channels) in nodes of Ranvier and initial segments of mammalian neurons. However, direct effects of ankyrin-G on electrophysiological properties of Nav channels remain elusive. In this study, we explored whether ankyrin-G has a role in modifying gating properties of the neuronal Nav1.6 channel that is predominantly localized at nodes of Ranvier and initial segments. TsA201 cells transfected with the human Nav1.6 cDNA alone exhibited significant persistent sodium current (Ina-p). On the other hand, Ina-p was barely detected on co-expression with ankyrin-G. Ankyrin-B, another ankyrin, did not show such an effect. Expression of chimeras between the two isoforms of ankyrin suggests that the membrane-binding domain of ankyrin-G is critical for reducing the Ina-p of Nav1.6. These results suggest that ankyrin-G regulates neuronal excitability not only through clustering Nav channels but also by directly modifying their channel gating.

Periaxin (PRX) plays a significant role in the myelination of the peripheral nerve. To date, seven nonsense or frameshift PRX mutations have been reported in six pedigrees with Dejerine-Sottas neuropathy or severe Charcot-Marie-Tooth neuropathy (CMT). We detected a PRX mutation in three patients in the screening of 66 Japanese demyelinating CMT patients who were negative for the gene mutation causing dominant or X-linked demyelinating CMT. Three unrelated patients were homozygous for a novel R1070X mutation and presented early-onset but slowly progressive distal motor and sensory neuropathies. Mutations lacking the carboxyl-terminal acidic domain may show loss-offunction effects and cause severe demyelinating CMT.

Recently, a few genetic abnormalities were identified in congenital central hypoventilation syndrome (CCHS or Ondine's curse). CCHS is often associated with other neurocristopathies, especially with Hirschsprung's disease (HSCR). Mutations of the genes involved in the receptor tyrosine kinase RET (REarranged during Transfection) (RET)-glial cell line-derived neurotrophic factor (GDNF) and/or endothelin 3 (EDN3)-endothelin receptor-B (EDNRB) signaling pathway have been found in some of HSCR patients. In this study, we analyzed candidates for HSCR, namely the RET, GDNF, EDN3 and EDNRB genes in three isolated CCHS patients to confirm the hypothesis that some CCHS patients have a common genetic abnormality with patients having HSCR or other neurocristopathies. We found a novel R114H mutation of the RET gene in one patient. The R114H mutation is unlikely to be a polymorphism and appears to be associated with CCHS. In addition, we also examined the HOX11L2 (RNX) gene, for which knock-out mice showed CCHS-like syndrome in these isolated CCHS patients and did not detected any mutation. Further cases should be analyzed for more candidates to clarify the pathophysiology of CCHS.

Shwachman-Diamond syndrome (SDS) is a rare hereditary disorder characterized by pancreatic exocrine insufficiency, bone marrow dysfunction and skeletal changes. Recently, the cause of SDS was identified as mutations of Shwachman-BodianDiamond syndrome gene (SBDS) and most mutations are caused by gene conversion between SBDS and its highly homologous pseudogene. Clinical variations especially in skeletal and bone marrow abnormalities are well known in this syndrome. To study the relationship between SBDS mutation and its clinical features, we analyzed 9 Japanese patients including one sibling and detected the three different SBDS mutations in 7 patients: a mutation that disrupts the donor splice site of intron 2, deletes 8bp of the exon 2 and produces premature termination (258+2 T > C), a dinucleotide change that replaces a lysine at 62nd amino acid to a termination codon (183-184 TA > CT), and a 4-bp deletion that causes premature termination by frameshift (292-295 delAAAG). The 5 patients represent compound heterozygotes of the 258+2 T > C and 183-184 TA > CT mutations. One patient is a compound heterozygote of the 258+2 T > C and 292-295 delAAAG mutations, and in the remaining one case only a 258+2 T > C mutation could be detected. Thus, the 258+2 T > C and 183-184 TA > CT mutations are prevalent among Japanese patients. No mutations were found in two cases, despite the clinical features. Of the 7 patients with SBDS mutations, persistent hematologic abnormalities and skeletal changes were not observed in 3 and 2 patients, respectively. Notably, clinical variations are present even among the patients with the identical genotype: compound heterozygotes of the 258+2 T >