The DISC1 gene at 1q42 has generated considerable interest in various psychiatric diseases, since a balanced translocation interrupting the gene was found to cosegregate with schizophrenia and related mental illnesses in a large Scottish pedigree. To date, linkage and association findings to this locus have been replicated in several study samples ascertained for psychotic disorders. However, the biological function of DISC1 in neuronal development would suggest a potential role for this gene also in other, early onset neuropsychiatric disorders. Here we have addressed the allelic diversity of the DISC1, DISC2 and TRAX genes, clustered in 1q42, in Finnish families ascertained for infantile autism (97 families, n affected = 138) and Asperger syndrome (29 families, n affected = 143). We established association between autism and a DISC1 intragenic microsatellite (D1S2709; P = 0.004). In addition, evidence for association to Asperger syndrome was observed with an intragenic single nucleotide polymorphism (SNP) of DISC1 (rs1322784; P = 0.0058), as well as with a three-SNP haplotype (P = 0.0013) overlapping the HEP3 haplotype, that was previously observed to associate with schizophrenia in Finnish families. The strongest associations were obtained with broad diagnostic categories for both disorders and with affected males only, in agreement with the previous sex-dependent effects reported for DISC1. These results would further support the involvement of DISC1 gene also in the etiopathogenesis of early onset neuropsychiatric disorders.

We have previously reported a robust association between an allelic haplotype of 'Disrupted in Schizophrenia 1' (DISC1) and schizophrenia in a nationwide collection of Finnish schizophrenia families. This specific DISC1 allele was later identified to associate with visual working memory, selectively in males. DISC1 association to schizophrenia has since been replicated in multiple independent study samples from different populations. In this study, we conditioned our sample of Finnish families for the presence of the Finnish tentative risk allele for DISC1 and re-analyzed our genome-wide scan data of 443 markers on the basis of this stratification. Two additional loci displayed an evidence of linkage (LOD > 3) and included a locus on 16p13, proximal to the gene encoding NDE1, which has been shown to biologically interact with DISC1. Although none of the observed linkages remained significant after multiple test correction through simulation, further analysis of NDE1 revealed an association between a tag-haplotype and schizophrenia (P = 0.00046) specific to females, which proved to be significant (P = 0.011) after multiple test correction. Our finding would support the concept that initial gene findings in multifactorial diseases will assist in the identification of other components of complex genetic etiology. Notably, this and other converging lines of evidence underline the importance of DISC1-related functional pathways in the etiology of schizophrenia.

Bipolar disorder (BPD) and schizophrenia (SCZ) have at least a partially convergent aetiology and thus may share genetic susceptibility loci. Multiple lines of evidence emphasize the role of disrupted-in-schizophrenia-1 (DISC1) gene in psychotic disorders such as SCZ. We monitored the association of allelic variants of translin-associated factor X (TSNAX)/DISC1 gene cluster using 13 single-nucleotide polymorphisms (SNPs) in 723 members of 179 Finnish BPD families. Consistent with an earlier finding in Finnish SCZ families, the haplotype T-A of rs751229 and rs3738401 at the 5' end of DISC1 was over-transmitted to males with psychotic disorder (P = 0.008; for an extended haplotype P = 0.0007 with both genders). Haplotypes at the 3' end of DISC1 associated with bipolar spectrum disorder (P = 0.0002 for an under-transmitted haplotype T-T of rs821616 and rs1411771, for an extended haplotype P = 0.0001), as did a two-SNP risk haplotype at the 5' end of TSNAX (P = 0.007). The risk haplotype for psychotic disorder also associated to perseverations (P = 0.035; for rs751229 alone P = 0.0012), and a protective haplotype G-T-G with rs1655285 in addition to auditory attention (P = 0.0059). The 3' end variants associated with several cognitive traits, with the most robust signal for rs821616 and verbal fluency and rs980989 and psychomotor processing speed (P = 0.011 for both). These results support involvement of DISC1 in the genetic aetiology of BPD and suggest that its distinct variants contribute to variation in the dimensional features of psychotic and bipolar spectrum disorders. Finding of alternative associating haplotypes in the same set of BPD families gives evidence for allelic heterogeneity within DISC1, eventually leading to heterogeneity in the clinical outcome as well.

and rs1170191 were quite similar in the Baum et al. 3 and in our control samples, allele frequencies of rs9315885 were moderately different (T-allele frequency: mean of the two samples = 0.67, Baum et al. 3 ; our sample = 0.53). Differences in allele frequencies might be explained by the fact that although Baum et al. 3 and our samples were both of Caucasian ancestry, our sample was consisting of subjects of Sardinian ancestry for at least four generation.In conclusion, the association for a DGKH haplotype reported in our sample, although intriguing, must be interpreted with caution and further studies need to be performed to clarify the role of DGKH in BD. Finally, the lack of association with the lithium response is far from being considered conclusive.

Bipolar disorder is highly heritable. Cognitive dysfunctions often observed in bipolar patients and their unaffected relatives implicate that these impairments may be associated with genetic predisposition to bipolar disorder and thus fulfill the criteria of a valid endophenotype for the disorder. However, the most fundamental criterion, their heritability, has not been directly studied in any bipolar population. This population-based study estimated the heritability of cognitive functions in bipolar disorder. A comprehensive neuropsychological test battery and the Structured Clinical Interview for DSM-IV were administered to a population-based sample of 110 individuals from 52 families with bipolar disorder. Heritability of cognitive functions as assessed with neuropsychological test scores were estimated using the Solar package. Significant additive heritabilities were found in verbal ability, executive functioning, and psychomotor processing speed. Genetic contribution was low to verbal learning functions. High heritability, in executive functioning and psychomotor processing speed suggest that these may be valid endophenotypic traits for genetic studies of bipolar disorder.