No evidence for an association between variants at the proline dehydrogenase locus and schizophrenia or bipolar affective disorder

Proline dehydrogenase gene (PRODH) polymorphisms and schizophrenia susceptibility: a meta-analysis

Previous studies have been conducted to explore the association between proline dehydrogenase gene (PRODH) polymorphisms and schizophrenia (SZ) susceptibility, but providing the controversial results. Here we performed this meta-analysis to determine whether PRODH variants were associated with SZ risk. Relevant studies were screened by retrieving online database PubMed, Web of Science, Embase, China National Knowledge Infrastructure (CNKI) and SZGene from inception to December 2016. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated based on genotype data or allele frequency to evaluate the strength of this association. For rs372055, eleven studies with 3398 SZ patients and 3171 controls were included and the results indicated that people carrying the T allele was not associated with SZ risk in allele frequency model (C vs T, OR = 1.12, 95%CI = 0.96-1.32). However, results from subgroup analysis showed a significant relationship between rs372055 and SZ risk in dominant genetic model (CC + CT vs TT, OR = 1.26, 95% CI = 1.05-1.50) and heterogeneous model (CT vs TT, OR = 1.26, 95% CI = 1.05-1.52) in Asian, but not in Caucasian. For polymorphisms rs383964, rs450046, rs385440 and rs2870983, no associations were found between these polymorphisms and SZ susceptibility in allele frequency. This meta-analysis suggests that rs372055 (C/T) polymorphism in PRODH gene is associated with increased SZ risk only in Asian.

Association of COMT and PRODH gene variants with intelligence quotient (IQ) and executive functions in 22q11.2DS subjects

The 22q11.2 deletion syndrome (22q11.2DS) carries the highest genetic risk factor for the development of schizophrenia. We investigated the association of genetic variants in two schizophrenia candidate genes with executive function (EF) and IQ in 22q11.2DS individuals. Ninety two individuals with 22q11.2 deletion were studied for the genetic association between COMT and PRODH variants and EF and IQ. Subjects were divided into children (under 12 years old), adolescents (between 12 and 18 years old) and adults (older than 18 years), and genotyped for the COMT Val158Met (rs4680) and PRODH Arg185Trp (rs4819756) polymorphisms. The participants underwent psychiatric evaluation and EF assessment. Our main finding is a significant influence of the COMT Val158Met polymorphism on both IQ and EF performance. Specifically, 22q11.2DS subjects with Met allele displayed higher IQ scores in all age groups compared to Val carriers, reaching significance in both adolescents and adults. The Met allele carriers performed better than Val carriers in EF tasks, being statistically significant in the adult group. PRODH Arg185Trp variant did not affect IQ or EF in our 22q11.2DS cohort. In conclusion, functional COMT variant, but not PRODH, affects IQ and EF in 22q11.2DS subjects during neurodevelopment with a maximal effect at adulthood. Future studies should monitor the cognitive performance of the same individuals from childhood to old age.

Cognitive, behavioural and psychiatric phenotype in 22q11.2 deletion syndrome

22q11.2 Deletion syndrome has become an important model for understanding the pathophysiology of neurodevelopmental conditions, particularly schizophrenia which develops in about 20-25% of individuals with a chromosome 22q11.2 microdeletion. From the initial discovery of the syndrome, associated developmental delays made it clear that changes in brain development were a key part of the expression. Once patients were followed through childhood into adult years, further neurobehavioural phenotypes became apparent, including a changing cognitive profile, anxiety disorders and seizure diathesis. The variability of expression is as wide as for the myriad physical features associated with the syndrome, with the addition of evolving phenotype over the developmental trajectory. Notably, variability appears unrelated to length of the associated deletion. Several mouse models of the deletion have been engineered and are beginning to reveal potential molecular mechanisms for the cognitive and behavioural phenotypes observable in animals. Both animal and human studies hold great promise for further discoveries relevant to neurodevelopment and associated cognitive, behavioural and psychiatric disorders.

Functional polymorphisms in PRODH are associated with risk and protection for schizophrenia and fronto-striatal structure and function

PRODH, encoding proline oxidase (POX), has been associated with schizophrenia through linkage, association, and the 22q11 deletion syndrome (Velo-Cardio-Facial syndrome). Here, we show in a family-based sample that functional polymorphisms in PRODH are associated with schizophrenia, with protective and risk alleles having opposite effects on POX activity. Using a multimodal imaging genetics approach, we demonstrate that haplotypes constructed from these risk and protective functional polymorphisms have dissociable correlations with structure, function, and connectivity of striatum and prefrontal cortex, impacting critical circuitry implicated in the pathophysiology of schizophrenia. Specifically, the schizophrenia risk haplotype was associated with decreased striatal volume and increased striatal-frontal functional connectivity, while the protective haplotype was associated with decreased striatal-frontal functional connectivity. Our findings suggest a role for functional genetic variation in POX on neostriatal-frontal circuits mediating risk and protection for schizophrenia.

Schizophrenia is a major mental illness affecting 1% of the population. It is known that genetics plays a role in the disease susceptibility, and it is thought that the illness is a complex disorder involving multiple genes. We show that the schizophrenia susceptibility gene, PRODH, conveys its risk through a variation that increases its enzyme activity. We further show that protection is associated with variations that decrease enzyme activity and these protective variations are enriched in their unaffected siblings. We then used brain imaging of structure and memory function to dissect the risk and protective haplotypes differential effects, and found that the schizophrenia risk haplotype was associated with decreased striatal gray matter volume and increased subcortical to frontal lobe functional connectivity, while the schizophrenia protective haplotype was associated with trend-level increase of frontal lobe volume and decreased subcortical to frontal lobe connectivity. These findings indicate a new target for treating schizophrenia and characterize associated structural and functional deficits.

Genomic structural variation and schizophrenia

It has recently been demonstrated that a large amount of structural variation exists in the human genome. Since 2004, when two landmark studies reported polymorphic levels of copy number variation in phenotypically normal individuals, our understanding of genome-wide levels of copy number variation has grown. This has inspired hypotheses about this class of variation's contribution to complex genetic phenotypes, including the specific hypothesis that structural variation is associated with psychiatric illness. The technology to accurately and efficiently detect polymorphic structural variants is still largely under development, but some examples of genomic imbalance contributing to schizophrenia and bipolar disorder already have been identified. Although much optimism surrounds this burgeoning field, the technical challenges in reliably identifying structural variation mean recent literature should be approached with caution.

Mouse models of 22q11 deletion syndrome

22q11 deletion syndrome (22q11DS) is caused by an interstitial chromosomal microdeletion that encompasses about 40 genes. It is the most common of the microdeletion syndromes. The clinical phenotype, which is complex and variable, includes specific congenital defects of the cardiovascular system, craniofacies, and immune system. In early childhood, patients manifest cognitive impairment, behavioral disorders, and delays in motor development and language acquisition. Adult patients have a high risk for developing serious psychiatric disorders, especially schizophrenia, schizoaffective disorder, and bipolar disorder. The great majority of patients have an identical or near identical chromosomal deletion, and genotype-phenotype correlations have not been established. Indeed, little progress was made toward resolving the complex clinical phenotype until the deletion was successfully modeled in the mouse. In recent years, through a variety of mouse mutants that carry multigene and single gene mutations, we have learned that mutation in a single gene, Tbx1, is responsible for most of the congenital defects seen in the mouse models and in patients. We now face a greater challenge as we attempt to use the mouse to address the pathogenesis of the behavioral and psychiatric disorders associated with 22q11DS. Significant progress has already been made, and recent studies in the mouse suggest that several genes from the deleted region affect behavior and might contribute to disease burden in patients.