Genetic and functional analyses identify DISC1 as a novel callosal agenesis candidate gene

Agenesis of the corpus callosum (AgCC) is a congenital brain malformation that occurs in approximately 1:1,000-1:6,000 births. Several syndromes associated with AgCC have been traced to single gene mutations; however, the majority of AgCC causes remain unidentified. We investigated a mother and two children who all shared complete AgCC and a chromosomal deletion at 1q42. We fine mapped this deletion and show that it includes Disrupted-in-Schizophrenia 1 (DISC1), a gene implicated in schizophrenia and other psychiatric disorders. Furthermore, we report a de novo chromosomal deletion at 1q42.13 to q44, which includes DISC1, in another individual with AgCC. We resequenced DISC1 in a cohort of 144 well-characterized AgCC individuals and identified 20 sequence changes, of which 4 are rare potentially pathogenic variants. Two of these variants were undetected in 768 control chromosomes. One of these is a splice site mutation at the 5' boundary of exon 11 that dramatically reduces full-length mRNA expression of DISC1, but not of shorter forms. We investigated the developmental expression of mouse DISC1 and find that it is highly expressed in the embryonic corpus callosum at a critical time for callosal formation. Taken together our results suggest a significant role for DISC1 in corpus callosum development.     

Novel association approach for determining the genetic predisposition to schizophrenia: Case-control resource and testing of a candidate gene

We have developed a two-tiered approach to elucidating the genetic predisposition to schizophrenia. The approach first involves the examination of candidate genes in a subset of schizophrenic individuals to identify DNA sequence variations of likely functional significance, i.e., that produce either structural alterations in the protein or affect the level of gene expression. Once identified, the prevalence of the aberrant allele is examined in a large group of unrelated schizophrenic cases and controls to assess whether a true disease association exists. Herein, we describe the establishment of a DNA bank on nearly 200 unrelated schizophrenic cases defined by DSM-III-R criteria and on over 300 unrelated, ethnically similar controls. Characteristics of the study sample are described. The study approach then is illustrated by testing known mutations in the phenylalanine hydroxylase gene, responsible for the autosomal recessive disease of phenylketonuria, in the case-control sample to determine if carriership of a mutant allele is associated with an increased risk of schizophrenia. Using PCR amplification of specific alleles (PASA), we screened 190 schizophrenic cases and 336 controls for two common point mutations in the phenylalanine hydroxylase gene. Two carriers were found among the controls, while none of the cases was shown to carry a mutant allele. Thus, carriership of either of two common mutations in the phenylalanine hydroxylase gene does not appear to be associated with an increased risk of schizophrenia. As additional candidate genes are tested in this case-control resource, adjustment for multiple comparisons will become crucial in order to reduce the chance of false positive findings. The ascertainment of auxillary groups of cases and controls with sequential hypothesis testing in these groups offers a technically feasible solution to the multiple comparisons problem. © 1993 Wiley-Liss, Inc.     

Genetic variants in the BDNF gene and therapeutic response to risperidone in schizophrenia patients: a pharmacogenetic study

Risperidone is a widely used atypical antipsychotic agent that produces considerable interindividual differences in patient response. We investigated the pharmacogenetic relationship between the brain-derived neurotrophic factor (BDNF) gene and response to risperidone in 127 Han Chinese schizophrenic patients. Three functional polymorphisms, (GT)_n dinucleotide repeat polymorphism, C-270T, and the rs6265G/A single-nucleotide polymorphism (SNP), were genotyped and analyzed for association, with reduction of Brief Psychiatric Rating Scale (BPRS) scores following an 8-week period of risperidone monotherapy. For individual polymorphic analysis, we found that the frequency of the 230-bp allele of the (GT)_n polymorphism was much higher in responders (47.95%) than in nonresponders (32.41%) and the difference was statistically significant even after Bonferroni''s adjustment (for the 230-bp allele: adjusted P=0.039). For haplotype-based analyses of the three polymorphisms, no positive finding was observed in the global test, but in specific haplotype tests, two haplotypes were also significantly related to response to risperidone (for haplotype 230-bp/C-270/rs6265G: P=0.0009; for haplotype 234-bp/C-270/rs6265A: P=0.043), indicating that patients with the 230-bp allele of the (GT)_n polymorphism or the 230-bp/C-270/rs6265G haplotype responded better to risperidone than those with other alleles or haplotypes, and that the positive effect of the individual haplotype 230-bp/C-270/rs6265G was mainly driven by the 230-bp allele. These findings demonstrate that the individual and combinatorial genetic variants in the BDNF gene might have a role in the therapeutic response to risperidone in the Han Chinese population.     

住院精神分裂症患者抗精神病药联合使用合理性的病例分析

目的:分析精神分裂症成年住院患者入院后抗精神病药联合使用的比例、具体联用的抗精神病药及其合理性。方法:2012年6月-2013年3月对2009年至2011年入住北京大学第六医院,符合美国精神障碍诊断和统计手册第4版(DSM-IV)诊断标准的精神分裂症成年患者171例,记录其人口学资料、所服抗精神病药、服用时间及出院情况。通过检索Pub Med,对抗精神病药的合理联用(有证据支持者)和通过查询Micromedex○R 2.0数据库,确定为重度违反该数据库(Micromedex○R 2.0为美国Thomson Healthcare按临床应用的需求制作的综述型事实数据库)的联用(可以致死和/或需要医疗干预的抗精神病药联用)对抗精神病药风险联用进行界定。而抗精神病药的不合理联用则是所有抗精神病药联用去除合理联用和风险联用者。结果:本组病例住院后接受抗精神病药联合治疗者占49.7%(85/171),其中合理联合使用占12.9%(11/85),不合理联合使用占68.2%(58/85),风险联用为18.8%(16/85)。结论:精神分裂症成年患者住院治疗期间抗精神病药联合使用常见,联用风险值得关注。     

Novel polymorphisms of the human cholecystokinin a receptor gene: An association analysis with schizophrenia

The cholecystokinin A receptor (CCK‐AR) modulates CCK‐stimulated dopamine release in the posterior nucleus accumbens, and its gene is mapped to 4p15.2‐15.1 with the dopamine receptor 5 (DR5) gene. We speculated that alterations in the CCK‐AR lead to an increase in dopamine release, which may in turn constitute a predisposition in schizophrenia. We investigated genetic variations in the promoter region and the coding region of the CCK‐AR gene. An association analysis was conducted between 83 unrelated schizophrenic patients and 80 healthy controls. Novel polymorphisms (201A→G, 246G→A in the promoter region, 1260T→A, 1266T→C in intron 1 within the 3′ mRNA splice acceptor site consensus sequence, and Leu306Leu in exon 5) were found in addition to the variants (608G→A in intron 1, 3849C→T [Ile296Ile] in exon 5) reported previously. Significant differences were found in the allele frequencies of the 201A→G nucleotide substitution in the promoter region between patients and controls (P = 0.0181, odds ratio: 1.972, after Bonferroni correction: P = 0.0543). These differences were also found between the patients with paranoid type and controls (P = 0.0274, odds ratio = 3.667, after Bonferroni correction: P = 0.0822). Our analyses suggest that the 201A allele frequency was higher in the schizophrenic group, especially in the paranoid type, than in the control group at a rate that was not quite significant after Bonferroni correction. Am J. Med Genet. (Neuropsychiatr. Genet.) 96:141–145, 2000. © 2000 Wiley‐Liss, Inc.     

A novel truncating variant p.(Arg297*) in the GRM1 gene causing autosomal-recessive cerebellar ataxia with juvenile-onset

GRM1 gene, that is located on 6q24.3, encodes the metabotropic glutamate receptor type 1 (mGluR1), a transmembrane protein highly expressed in cerebellar Purkinje cells. Pathogenic variants in GRM1 have been reported only three times in humans, causing autosomal-recessive cerebellar ataxia with early-onset and intellectual disability or dominant forms of cerebellar ataxia with less severe phenotype in adults. We report a six-year-old boy, born to inbred parents, with an early-onset cerebellar syndrome due to a homozygous autosomal-recessive GRM1 pathogenic variant. In addition to cerebellar ataxia, axial hypotonia and oculomotor signs, he showed a severe and global developmental delay with lack of walking and speech and slight facial dysmorphic features. Brain MRI, performed at 1 year and at 5 years, showed a slowly progressive cerebellar atrophy. A novel homozygous truncating variant in the second exon of GRM1 gene (c.889C>T, p.(Arg297*)), inherited from the heterozygous healthy parents, was found by exome sequencing. Our observation not only emphasizes the central role of mGluR1-mediated signaling in cerebellar function and neurodevelopment but also provides valuable insights into the early clinical signs of recessive ataxia due to GRM1 pathogenic variants that were not reported previously. The difficulties of clinical differential diagnosis between this disease and other forms of congenital ataxia and the unspecific cerebellar atrophy on MRI highlight the importance of large-scale genetic investigations.     

Fine mapping of whole RB1 gene deletions in retinoblastoma patients confirms PCDH8 as a candidate gene for psychomotor delay

Retinoblastoma (Rb) results from inactivation of both alleles of the RB1 gene located in 13q14.2. Whole-germline monoallelic deletions of the RB1 gene (6% of RB1 mutational spectrum) sometimes cause a variable degree of psychomotor delay and several dysmorphic abnormalities. Breakpoints in 12 Rb patients with or without psychomotor delay were mapped to specifically define the role of chromosomal regions adjacent to RB1 in psychomotor delay. A high-resolution CGH array focusing on RB1 and its flanking region was designed to precisely map the deletion. Comparative analysis detected a 4-Mb critical interval, including a candidate gene protocadherin 8 (PCDH8). PCDH8 is thought to function in signalling pathways and cell adhesion in a central nervous system-specific manner, making loss of PCDH8 one of the probable causes of psychomotor delay in RB1-deleted patients. Consequently, we propose to systematically use high-resolution CGH in cases of partial or complete RB1 deletion encompassing the telomeric flanking region to characterize the putative loss of PCDH8 and to better define genotype/phenotype correlations, eventually leading to optimized genetic counselling and psychomotor follow-up.     

Mutational analysis of the human SLC26A8 gene: exclusion as a candidate for male infertility due to primary spermatogenic failure

SLC26A8 is an anion transporter that is solely expressed in the testes. It interacts with MgcRacGAP that shows strong structural similarity with the Drosophila protein RotundRacGAP, which is established to have an essential role for male fertility in the fruit fly. To explore whether the SLC26A8 gene has a role in human male infertility, we performed mutational analysis in the coding region of the SLC26A8 gene in 83 male infertility patients and two groups of controls using single-strand conformational polymorphism and direct sequencing methods. We found six novel coding sequence variations, of which five lead to amino acid substitutions. All variants were found with similar frequencies in both patients and controls, thus suggesting that none of them may be causally associated with infertility. We conclude that the SLC26A8 mutations are not a common cause of male infertility.     

Elucidation of CYP2D6 Genetic Diversity in a Unique African Population: Implications for the Future Application of Pharmacogenetics in the Xhosa Population

Genetic variation of the CYP2D6 gene has been associated with altered drug metabolism; however, limited studies have investigated CYP2D6 sequence diversity in African populations. We devised a CYP2D6 genotyping strategy to analyse the South African Xhosa population and genotype a Xhosa schizophrenia cohort, as CYP2D6 metabolises many antipsychotics and antidepressants. The entire CYP2D6 gene locus was sequenced in 15 Xhosa control individuals and the data generated were used to design a comprehensive genotyping strategy. Over 25 CYP2D6 alleles were genotyped in Xhosa controls and Xhosa schizophrenia patients using long‐range PCR, DNA sequencing and single nucleotide primer extension analysis. Bioinformatic algorithms were used to predict the functional consequences of relevant mutations and samples were assigned CYP2D6 activity scores. A unique allele distribution was revealed and two rare novel alleles, CYP2D6*73 and CYP2D6*74, were identified. No significant differences in allele frequencies were detected between Xhosa controls and schizophrenia patients. This study provides i) comprehensive data on a poorly characterised population, ii) a valuable CYP2D6 genotyping strategy and iii) due to their unique genetic profile, provides the basis for pharmacogenetic intervention for Xhosa individuals.     

Testing the effects of FSHD candidate gene expression in vertebrate muscle development

The genetic lesion leading to facioscapulohumeral muscular dystrophy (FSHD) is a dominant deletion at the 4q35 locus. The generally accepted disease model involves an epigenetic dysregulation in the region resulting in the upregulation of one or more proximal genes whose overexpression specifically affects skeletal muscle. However, multiple FSHD candidate genes have been proposed without clear consensus. Using Xenopus laevis as a model for vertebrate development our lab has studied the effects of overexpression of the FSHD candidate gene ortholog, frg1 (FSHD region gene 1), showing that increased levels of frg1 systemically led specifically to an abnormal musculature and increased angiogenesis, the two most prominent clinical features of FSHD. Here we studied the overexpression effects of three other promising FSHD candidate genes, DUX4, DUX4c, and PITX1 using the same model system and methods for direct comparison. Expression of even very low levels of either DUX4 or pitx1 early in development led to massive cellular loss and severely abnormal development. These abnormalities were not muscle specific. In contrast, elevated levels of DUX4c resulted in no detectable adverse affects on muscle and DUX4c levels did not alter the expression of myogenic regulators. This data supports a model for DUX4 and PITX1 in FSHD only as pro-apoptotic factors if their expression in FSHD is confined to cells within the myogenic pathway; neither could account for the vascular pathology prevalent in FSHD. Taken together, increased frg1 expression alone leads to a phenotype that most closely resembles the pathophysiology observed in FSHD patients.     

BAZ1B is a candidate gene responsible for hypothyroidism in Williams syndrome

Williams syndrome (WS) is a rare neurodevelopmental disorder associated to a hemizygous deletion of 28 genes located on chromosome 7q11.23. WS affected subjects frequently suffer from several endocrine abnormalities including hypothyroidism due to defects in thyroid morphology. To date, several genes involved in thyroid dysgenesis have been identified, nonetheless, none of them is located in the 7q11.23 region. Thus, the hypothyroidism-linked molecular features in WS are not yet known. In this study we focused on one of the WS deleted gene, BAZ1B, demonstrating that its downregulation in thyroid cells leads to cell viability and survival decrement. Taking together, our results show that BAZ1B could be the mainly responsible for thyroid defects observed in some of WS patients and that these alterations are activated by PTEN-mediated mechanisms.     

Mutation screening of the 3q29 microdeletion syndrome candidate genes DLG1 and PAK2 in schizophrenia

Deletion of chromosome 3q29, which is associated with mental retardation and autism, was recently identified as being present in excess or occurring de novo in schizophrenia cases, being present in approximately 1/1,000 cases and 1/40,000 unscreened controls. Of the ～20 genes in the commonly deleted region two are prominent candidates for involvement in the behavioral features of the microdeletion syndrome: DLG1 and PAK2. We report the result of mutation screening of the entire protein coding sequence of both genes in a sample of 234 unrelated cases and 272 unrelated controls from the UK. We find no evidence for any amino acid changing genetic variants in PAK2. We observe several rare and singleton non‐synonymous genetic variations at DLG1, however there is no excess of these variants in cases when compared to controls. Our sample was underpowered to detect very rare or low‐penetrance disease relevant alleles in the studied genes. Therefore very rare, low‐to‐moderate penetrance protein coding mutations or non‐coding mutations at DLG1 and/or PAK2, or a nearby gene, may reproduce the behavioral characteristics of the 3q29 microdeletion. © 2011 Wiley‐Liss, Inc.     

Neuregulin 1基因多态性与中国汉族精神分裂症关联分析

目的 探讨Neuregulin 1(NRG1)基因多态性与精神分裂症的关联.方法 在258个中国汉族精神分裂症核心家系(患者及其亲生父母)中,应用实时定量PCR技术检测位于NRGl基因5'端的4个单核苷酸多态(single nucleotide polymorphism,SNP)位点:rs221533(C/T)、rs7820838(C/T)、433E1006 (A/G)和rs3924999(C/T),进行基因分型,应用传递不平衡检测(transmission disequilibrium test,TDT)分析等位基因传递情况,分析该基因与精神分裂症易感性的关联.结果 在258个中国汉族核心家系中,rs221533、433E1006、rs3924999三个SNP均存在有统计学意义的传递不平衡,优先传递的等位基因分别是:C、A、T(rs221533:X2=27.45,P=0.000;433E1006:X2=56.08,P=0.000;rs3924999:X2=10.53,P=0.001).rs7820838未检到不平衡传递(X2=3.31,P=0.081).频率大于1%单倍型进行分析,rs221533-rs7820838-433E1006联合分析,单倍型C/C/G和C/C/A优先传递(C/C/G:X2=5.26,P=45.08;C/C/A:X2=0.026,P=0.000);rs221533-rs7820838-433E1006-rs3924999联合分析,单倍型C/C/G/T、C/C/A/C和C/C/A/T优势传递(C/C/G/T:X2=10.71,P=0.001;C/C/A/C:.)X2=8.83,P=0.006、C/C/A/T:X2=27.00,P=0.000).213个阳性亚型的精神分裂症核心家系中传递不平衡得出基本一致的结果 .结论 Nrg1基因多态性与中国汉族人群精神分裂症存在关联,尤其是支持与阳性亚型精神分裂症存在关联.     

Investigation of the CACNA1A gene as a candidate for typical migraine susceptibility

Typical migraine is a complex neurological disorder comprised of two main subtypes: migraine with (MA) and without aura (MO). The disease etiology is still unclear, but family studies provide strong evidence that defective genes play an important role. Familial hemiplegic migraine (FHM) is a very rare and severe subtype of MA. It has been proposed that FHM and MA may have a similar genetic etiology. Therefore, genetic studies on FHM provide a useful model for investigating the more prevalent types of typical migraine. FHM in some families has been shown to be caused by mutations in a brain‐specific P/Q‐type calcium channel α1 subunit gene (CACNA1A) on chromosome 19p13. There has also been a report of a CACNA1A mutation being associated with MA in a patient from a family with predominant FHM. We have previously demonstrated suggestive linkage of typical migraine in a large Australian family to the FHM region on chromosome 19p13. These findings suggest that CACNA1A may also be implicated in the etiology of typical migraine in this pedigree. To investigate this possibility, we sequenced two patients carrying the critical susceptibility haplotype surrounding CACNA1A. No disease‐causing mutations or polymorphisms were revealed in any of the 47 exons screened. To determine whether the CACNA1A gene was implicated in typical migraine susceptibility in the general Caucasian population, we also analyzed 82 independent pedigrees and a large case control group. We did not detect any linkage or association in these groups and conclude that if CACNA1A plays a role in typical migraine, it does not confer a major effect on the disease. © 2001 Wiley‐Liss, Inc.