Association of common copy number variants at the glutathione S-transferase genes and rare novel genomic changes with schizophrenia.

Copy number variants (CNVs) are a substantial source of human genetic diversity, influencing the variable susceptibility to multifactorial disorders. Schizophrenia is a complex illness thought to be caused by a number of genetic and environmental effects, few of which have been clearly defined. Recent reports have found several low prevalent CNVs associated with the disease. We have used a multiplex ligation-dependent probe amplification-based (MLPA) method to target 140 previously reported and putatively relevant gene-containing CNV regions in 654 schizophrenic patients and 604 controls for association studies. Most genotyped CNVs (95%) showed very low (<1%) population frequency. A few novel rare variants were only present in patients suggesting a possible pathogenic involvement, including 1.39 Mb overlapping duplications at 22q11.23 found in two unrelated patients, and duplications of the somatostatin receptor 5 gene (SSTR5) at 16p13.3 in three unrelated patients. Furthermore, among the few relatively common CNVs observed in patients and controls, the combined analysis of gene copy number genotypes at two glutathione S-transferase (GST) genes, GSTM1 (glutathione S-transferase mu 1) (1p13.3) and GSTT2 (glutathione S-transferase theta 2) (22q11.23), showed a statistically significant association of non-null genotypes at both loci with an additive effect for increased vulnerability to schizophrenia (odds ratio of 1.92; P=0.0008). Our data provide complementary evidences for low prevalent, but highly penetrant chromosomal variants associated with schizophrenia, as well as for common CNVs that may act as susceptibility factors by disturbing glutathione metabolism.

Complete deletion of ornithine transcarbamylase gene confirmed by CGH array of X chromosome.

Ornithine transcarbamylase deficiency is an X-linked semidominant trait that is the most frequent inborn error of the urea cycle. Three hundred and fifty different mutations, including mostly point mutations and a small proportion of large rearrangements have been reported. Conventional molecular diagnosis is highly reliable for point mutations but can miss gross rearrangements. We describe a contiguous gene syndrome involving the RPGR, OTC and TM4SF2 genes in a male patient with severe neonatal OTC deficiency identified by the conventional molecular approach. Molecular characterization was ascertained by X chromosome CGH array and confirmed by MLPA. Complete deletion of the OTC gene led to absent OTC enzymatic activity in liver and to a severe clinical phenotype. The maternal phenotype, characterized by less severe hyperammonaemic crises associated with neurological impairment would result from a deficient but not null OTC activity due to random X chromosome inactivation in the liver. Our cases are similar toothers described presenting with OTC deficient phenotype in which OTC and contiguous genes are affected. Clinical expression would be conditioned by complete OTC deficiency in males and by X chromosome inactivation in females, leading to compensation by the normal allele in tissues such as blood or muscle but not sufficiently in liver. The application of high-resolution genetic techniques allows the characterization of causative mutations such as large deletions in order to guide genetic counselling and prenatal diagnosis.