Association of the Hermansky-Pudlak syndrome type 4 (HPS4) gene variants with cognitive function in patients with schizophrenia and healthy subjects.

BACKGROUND: The Hermansky-Pudlak Syndrome Type 4 (HPS4) gene, which encodes a subunit protein of the biogenesis of lysosome-related organelles complex (BLOC)-3, which is involved in late endosomal trafficking, is associated with schizophrenia; however, its clinical relevance in schizophrenia remains unknown. The purpose of the present study was to investigate whether HPS4 is associated with cognitive functions in patients with schizophrenia and healthy controls and with the clinical profiles of patients with schizophrenia. METHODS: We investigated the association of variants of HPS4 with clinical symptoms and cognitive function in Japanese patients with schizophrenia (n = 240) and age-matched healthy control subjects (n = 240) with single nucleotide polymorphisms (SNP)- or haplotype-based linear regression. We analyzed five tagging SNPs (rs4822724, rs61276843, rs9608491, rs713998, and rs2014410) of HPS4 and 2-5 locus haplotypes of these five SNPs. The cognitive functions of patients and healthy subjects were evaluated with the Brief Assessment of Cognition in Schizophrenia, Japanese-language version, and the patients were assessed for their symptomatology with the Positive and Negative Symptom Scale (PANSS). RESULTS: In patients with schizophrenia, rs713998 was significantly associated with executive function under the dominant genetic model (P = 0.0073). In healthy subjects, there was a significant association between working memory and two individual SNPs under the recessive model (rs9608491: P = 0.001; rs713998: P = 0.0065) and two haplotypes (rs9608491-713998: P = 0.0025; rs61276843-9608491-713998: P = 0.0064). No significant association was found between HPS4 SNPs and PANSS scores or premorbid IQ, as measured by the Japanese version of the National Adult Reading Test. CONCLUSIONS: These findings suggested the involvement of HPS4 in the working memory of healthy subjects and in the executive function deficits in schizophrenia.

An association study of the Hermansky-Pudlak syndrome type 4 gene in schizophrenic patients.

OBJECTIVE: We encountered two Japanese siblings who had Hermansky-Pudlak syndrome (HPS) and major mental disorders (schizophrenia and major depression) as well. As it is known that HPS is caused by a local mutation in one of the human genes, named HPS1 to HPS8 and PLDN (HPS9), encoding subunit proteins involved in endosomal trafficking pathways, here, we report the mutation causing the siblings disease and a case-control association study of schizophrenia using polymorphisms of a gene to be screened in the mutation analysis. METHODS: We analyzed three HPS-causing genes, HPS1, HPS4, and HPS7, to identify a genetic mutation involved in the siblings. A case-control association study of nine tagging single-nucleotide polymorphisms of the entire genetic region of the HPS4 gene resulting from the screening in the siblings was carried out for schizophrenic patients (n=422) and controls (n=578). RESULTS: The two patients with HPS were homozygous for nonsense mutation (T/T) for the c.541C>T (rs119471022) in the HPS4 gene, which is mapped to human chromosome 22q12.1. The same nonsense mutation existed in the heterozygous state (C/T) in their mother and in two other siblings. The genotypic distribution of rs9608491 (C/T) in intron 4 showed a trend toward an association with schizophrenia as indicated by a corrected P-value of 0.053 controlling for multiple testing. Haplotype analyses showed that two of two-locus haplotypes, and all of three-locus, four-locus, and five-locus haplotypes, as they share rs9608491, yielded significant evidence for association with schizophrenia as shown by the following omnibus P-values. When rs4822724, rs61276843, rs9608491, rs713998, and rs2014410, five haplotype tagging single-nucleotide polymorphisms, are assigned serial numerals (1, 2, 3, 4, and 5), the omnibus P-values for the resulting haplotypes were P=0.0039 for 2-3, P=0.0142 for 3-4, P=0.0083 for 1-2-3, P=0.0187 for 2-3-4, P=0.0191 for 3-4-5, P=0.0270 for 1-2-3-4, P=0.0246 for 2-3-4-5, and 0.0261 for 1-2-3-4-5. CONCLUSION: These results suggest that the HPS4 gene confers a susceptibility to schizophrenia.

Genetics of bipolar disorder.

Many linkage loci and candidate genes have been reported in molecular genetic studies of bipolar disorder. However, none of these findings have been consistently replicated. Meta-analyses of linkage studies have also reported conflicting results. Among recently reported candidate genes, BDNF, G72, AKT1, GRIN2A, XBP1, GRK3, HTR4, IMPA2 and GABRA1 may have some importance. Study of the possible roles of epigenetics or analysis of genetic diseases, in which bipolar disorder is one of phenotypes, may also be promising. In addition to monoaminergic and intracellular signaling pathways, recent studies have revealed possible roles for mitochondrial dysfunction, for glutamatergic dysfunction and for the endoplasmic reticulum stress pathway.

NEDD4-2 (neural precursor cell expressed, developmentally down-regulated 4-2) negatively regulates TGF-beta (transforming growth factor-beta) signalling by inducing ubiquitin-mediated degradation of Smad2 and TGF-beta type I receptor.

Inhibitory Smad, Smad7, is a potent inhibitor of TGF-beta (transforming growth factor-beta) superfamily signalling. By binding to activated type I receptors, it prevents the activation of R-Smads (receptor-regulated Smads). To identify new components of the Smad pathway, we performed yeast two-hybrid screening using Smad7 as bait, and identified NEDD4-2 (neural precursor cell expressed, developmentally down-regulated 4-2) as a direct binding partner of Smad7. NEDD4-2 is structurally similar to Smurfs (Smad ubiquitin regulatory factors) 1 and 2, which were identified previously as E3 ubiquitin ligases for R-Smads and TGF-beta superfamily receptors. NEDD4-2 functions like Smurfs 1 and 2 in that it associates with TGF-beta type I receptor via Smad7, and induces its ubiquitin-dependent degradation. Moreover, NEDD4-2 bound to TGF-beta-specific R-Smads, Smads 2 and 3, in a ligand-dependent manner, and induced degradation of Smad2, but not Smad3. However, in contrast with Smurf2, NEDD4-2 failed to induce ubiquitination of SnoN (Ski-related novel protein N), although NEDD4-2 bound to SnoN via Smad2 more strongly than Smurf2. We showed further that overexpressed NEDD4-2 prevents transcriptional activity induced by TGF-beta and BMP, whereas silencing of the NEDD4-2 gene by siRNA (small interfering RNA) resulted in enhancement of the responsiveness to TGF-beta superfamily cytokines. These data suggest that NEDD4-2 is a member of the Smurf-like C2-WW-HECT (WW is Trp-Trp and HECT is homologous to the E6-accessory protein) type E3 ubiquitin ligases, which negatively regulate TGF-beta superfamily signalling through similar, but not identical, mechanisms to those used by Smurfs.