Evidence for linkage to chromosome 13q32 in an independent sample of schizophrenia families

Intracellular Fibroblast Growth Factor 14: Emerging Risk Factor for Brain Disorders

The finely tuned regulation of neuronal firing relies on the integrity of ion channel macromolecular complexes. Minimal disturbances of these tightly regulated networks can lead to persistent maladaptive plasticity of brain circuitry. The intracellular fibroblast growth factor 14 (FGF14) belongs to the nexus of proteins interacting with voltage-gated Na+ (Na_v) channels at the axonal initial segment. Through isoform-specific interactions with the intracellular C-terminal tail of neuronal Na_v channels (Na_v1.1, Na_v1.2, Na_v1.6), FGF14 controls channel gating, axonal targeting and phosphorylation in neurons effecting excitability. FGF14 has been also involved in synaptic transmission, plasticity and neurogenesis in the cortico-mesolimbic circuit with cognitive and affective behavioral outcomes. In translational studies, interest in FGF14 continues to rise with a growing list of associative links to diseases of the cognitive and affective domains such as neurodegeneration, depression, anxiety, addictive behaviors and recently schizophrenia, suggesting its role as a converging node in the etiology of complex brain disorders. Yet, a full understanding of FGF14 function in neurons is far from being complete and likely to involve other functions unrelated to the direct regulation of Na_v channels. The goal of this Mini Review article is to provide a summary of studies on the emerging role of FGF14 in complex brain disorders.

Post-axial polydactyly type A2, overgrowth and autistic traits associated with a chromosome 13q31.3 microduplication encompassing miR-17-92 and GPC5

Genomic rearrangements at chromosome 13q31.3q32.1 have been associated with digital anomalies, dysmorphic features, and variable degree of mental disability. Microdeletions leading to haploinsufficiency of miR17∼92, a cluster of micro RNA genes closely linked to GPC5 in both mouse and human genomes, has recently been associated with digital anomalies in the Feingold like syndrome. Here, we report on a boy with familial dominant post-axial polydactyly (PAP) type A, overgrowth, significant facial dysmorphisms and autistic traits who carries the smallest germline microduplication known so far in that region. The microduplication encompasses the whole miR17∼92 cluster and the first 5 exons of GPC5. This report supports the newly recognized role of miR17∼92 gene dosage in digital developmental anomalies, and suggests a possible role of GPC5 in growth regulation and in cognitive development.

Linkage replication for chromosomal region 13q32 in schizophrenia: evidence from a Brazilian pilot study on early onset schizophrenia families

We report analyses of a Brazilian study of early onset schizophrenia (BEOS) families. We genotyped 22 members of 4 families on a linkage SNP array and report here non-parametric linkage analyses using MERLIN® software. We found suggestive evidence for linkage on two chromosomal regions, 13q32 and 11p15.4. A LOD score of 2.71 was observed at 13q32 with a one LOD interval extending from 60.63–92.35 cM. From simulations, this LOD score gave a genome-wide empirical corrected p = 0.33, after accounting for all markers tested. Similarly 11p15.4 showed the same maximum LOD of 2.71 and a narrower one LOD interval of 4–14 cM. Of these, 13q32 has been reported to be linked to schizophrenia by multiple different studies. Thus, our study provides additional supporting evidence for an aetiological role of variants at 13q32 in schizophrenia.

R, Elston R. Some capabilities for model-based and model-free linkage analysis using the program package S.A.G.E. (Statistical Analysis for Genetic Epidemiology)

For both model-free and model-based linkage analysis the S.A.G.E. (Statistical Analysis for Genetic Epidemiology) program package has some unique capabilities in analyzing both continuous traits and binary traits with variable age of onset. Here we highlight model-based linkage analysis of a quantitative trait (plasma dopamine β hydroxylase) that is known to be largely determined by monogenic inheritance, using a prior segregation analysis to produce the best fitting model for the trait. For a binary trait with variable age of onset (schizophrenia), we illustrate how using age of onset information to obtain a quantitative susceptibility trait leads to more statistically significant linkage signals, suggesting better power.

DAOA variants and schizophrenia: influence on diagnosis and treatment outcomes

OBJECTIVE

The present study explored whether d-amino acid oxidase activator (DAOA) variants were associated with schizophrenia and whether they could predict the clinical outcomes of patients treated with various antipsychotics.

METHODS

Two hundred and twenty-one (221) patients with schizophrenia and 170 psychiatrically healthy controls were genotyped for seven DAOA single-nucleotide polymorphisms (SNPs) (rs3916966, rs3916967, rs2391191, rs3916968, rs7139958, rs9558571 and rs778293). We also administered baseline and final clinical measures, including the Positive and Negative Symptoms Scale (PANSS), to patients with schizophrenia.

RESULTS

None of the SNPs under investigation was associated with the development of schizophrenia. However, the rs7139958 AA and rs9558571 TT as well as the rs7139958 A and rs9558571 T genotypes were associated with higher scores on the PANSS positive subscale among patients with schizophrenia, possibly reflecting their greater susceptibility to the development of more severe positive symptoms. No other allele, genotype, or haplotype under investigation was significantly associated with any of the clinical parameters, including clinical improvement, in patients with schizophrenia.

CONCLUSION

Our results suggested that rs7139958 and rs9558571 SNPs may be associated with more severe baseline positive symptoms in patients with schizophrenia. However, further research is needed to draw more definitive conclusions given the limitations of our study.

Possible association of different G72/G30 SNPs with mood episodes and persecutory delusions in bipolar I Romanian patients

The G72/G30 gene is one of the common loci shared both by schizophrenia and bipolar disorder. Studies accumulating since the discovery of this gene complex produced controversial results in both disorders in different populations.

OBJECTIVE

We investigated the association between the G72/G30 gene and bipolar I disorder (BPI) in the Romanian population paying special attention to the association of G72/G30 with lifetime psychosis and in particular with persecutory delusions in BPI patients.

METHOD

Fourteen G72/G30-SNPs were genotyped in a Romanian sample of 198 BPI patients and 180 controls screened for psychiatric disorders. Statistical analysis was performed with FAMHAP and HAPLOVIEW-v3.32. The significance level of the results was corrected through permutations in 100,000 simulations.

RESULTS

None of the fourteen SNPs was associated with the global diagnosis of BPI in our total patient sample or with the psychotic BPI subtype. When confining the psychotic phenotype to persecutory delusions, we observed trends to association for SNPs previously associated with schizophrenia and persecutory delusions in BPI [M21 (P=0.080); M22 (P=0.092; P=0.042 under dominant transmission model); M24 (P=0.092)]. Four SNPs reached nominal significance in the non-psychotic BPI subgroup [rs3916965 (M12) (P=0.044), rs1935057 (P=0.037), rs3916967 (M14) (P=0.043), and rs2391191 (M15, non-synonymous) (P=0.043)]. After correction through permutations, the haploblock GA including M14 and M15 showed a trend to association with BPI (P=0.0524; OR=1.82) in the non-psychotic BPI subgroup.

CONCLUSION

We report a potential association of different G72/G30-SNPs with non-psychotic mood episodes and with persecutory delusions in BPI Romanian patients. The results represent a first partial replication of two studies: Williams et al. (2006) and Schulze et al. (2005). The results have just a suggestive value since the Bonferroni correction for multiple testing was not applied.

A linkage search for joint panic disorder/bipolar genes

There is comorbidity and a possible genetic connection between Bipolar disease (BP) and panic disorder (PD). Genes may exist that increase risk to both PD and BP. We explored this possibility using data from a linkage study of PD (120 multiplex families; 37 had > or =1 BP member). We calculated 2-point lodscores maximized over male and female recombination fractions by classifying individuals with PD and/or BP as affected (PD + BP). Additionally, to shed light on possible heterogeneity, we examine the pedigrees containing a bipolar member (BP+) separately from those that do not (BP-), using a Predivided-Sample Test (PST). Linkage evidence for common genes for PD + BP was obtained on chromosomes 2 (lodscore = 4.6) and chromosome 12 (lodscore = 3.6). These locations had already been implicated using a PD-only diagnosis, although at both locations this was larger when a joint PD + BP diagnosis was used. Examining the BP+ families and BP- families separately indicates that both BP+ and BP- pedigrees are contributing to the peaks on chromosomes 2 and 12. However, the PST indicates different evidence of linkage is obtained from BP+ and BP- pedigrees on chromosome 13. Our findings are consistent with risk loci for the combined PD + BP phenotype on chromosomes 2 and 12. We also obtained evidence of heterogeneity on chromosome 13. The regions on chromosomes 12 and 13 identified here have previously been implicated as regions of interest for multiple psychiatric disorders, including BP.

Evidence for the association of the DAOA (G72) gene with schizophrenia and bipolar disorder but not for the association of the DAO gene with schizophrenia

Background

Previous linkage and association studies have implicated the D-amino acid oxidase activator gene (DAOA)/G30 locus or neighbouring region of chromosome 13q33.2 in the genetic susceptibility to both schizophrenia and bipolar disorder. Four single nucleotide polymorphisms (SNPs) within the D-amino acid oxidase (DAO) gene located at 12q24.11 have also been found to show allelic association with schizophrenia.

Methods

We used the case control method to test for genetic association with variants at these loci in a sample of 431 patients with schizophrenia, 303 patients with bipolar disorder and 442 ancestrally matched supernormal controls all selected from the UK population.

Results

Ten SNPs spanning the DAOA locus were genotyped in these samples. In addition three SNPs were genotyped at the DAO locus in the schizophrenia sample. Allelic association was detected between the marker rs3918342 (M23), 3' to the DAOA gene and both schizophrenia (χ² = 5.824 p = 0.016) and bipolar disorder (χ² = 4.293 p = 0.038). A trend towards association with schizophrenia was observed for two other DAOA markers rs3916967 (M14, χ² = 3.675 p = 0.055) and rs1421292 (M24; χ² = 3.499 p = 0.062). A test of association between a three marker haplotype comprising of the SNPs rs778293 (M22), rs3918342 (M23) and rs1421292 (M24) and schizophrenia gave a global empirical significance of p = 0.015. No evidence was found to confirm the association of genetic markers at the DAO gene with schizophrenia.

Conclusion

Our results provide some support for a role for DAOA in susceptibility to schizophrenia and bipolar disorder.

Chromosome 13q13-q14 locus overlaps mood and psychotic disorders: the relevance for redefining phenotype

The nosology of major psychoses is challenged by the findings that schizophrenia (SZ) and bipolar disorder (BP) share several neurobiological, neuropsychological and clinical phenotypic characteristics. Moreover, several vulnerability loci or genes may be common to the two DSM disorders. We previously reported, in a sample of 21 kindreds (sample 1), a genome-wide suggestive linkage in 13q13-q14 with a common locus (CL) phenotype that crossed the diagnostic boundaries by combining SZ, BP and schizoaffective disorders. Our objectives were to test phenotype specificity in a separate sample (sample 2) of 27 kindreds from Eastern Quebec and to also analyze the combined sample of 48 kindreds (1274 family members). We performed nonparametric and parametric analyses and tested as phenotypes: SZ alone, BP alone, and a CL phenotype. We replicated in sample 2 our initial finding with CL with a maximum NPL(pair) score of 3.36 at D13S1272 (44 Mb), only 2.1 Mb telomeric to our previous maximum result. In the combined sample, the peak with CL was at marker D13S1297 (42.1 Mb) with a NPL(pair) score reaching 5.21, exceeding that obtained in each sample and indicating consistency across the two samples. Our data suggest a susceptibility locus in 13q13-q14 that is shared by schizophrenia and mood disorder. That locus would be additional to another well documented and more distal 13q locus where the G72/G30 gene is mapped.

The G72/G30 gene locus in psychiatric disorders: a challenge to diagnostic boundaries?

In follow-up from evidence obtained in linkage studies, systematic linkage disequilibrium mapping within chromosomal region 13q33 has led to the identification of a schizophrenia susceptibility locus which harbors the genes G72 and G30. These association findings have been replicated in several independent schizophrenia samples. Association has also been found between genetic variants at the G72/G30 locus and bipolar affective disorder (BPAD), with replication in independent studies. Results from studies of more detailed psychiatric phenotypes show that association exists with symptom clusters that are common to several disorders as well as with specific psychiatric diagnoses. These findings may indicate that the association lies not with the diagnostic categories per se but with more specific aspects of the phenotype, such as affective symptoms and cognitive effects, which cross traditional psychiatric diagnostic boundaries. At the molecular level, the picture remains far from clear. No putative functional variants have been identified in the coding regions of G72 or G30, and it is therefore likely that disease susceptibility is caused by as yet unidentified variants which alter gene expression or splicing. A further complication is the fact that inconsistencies are evident in the risk alleles and haplotypes observed to be associated across different samples and studies, which may suggest the presence of multiple susceptibility variants at this locus. Functional analyses indicate that the G72 gene product plays a role in the activation of N-methyl-D-aspartate receptors, a molecular pathway implicated in both schizophrenia and BPAD, making it the most plausible candidate gene at this locus.