Review of bipolar molecular linkage and association studies

Association study of 21 circadian genes with bipolar I disorder, schizoaffective disorder, and schizophrenia

OBJECTIVE

Published studies suggest associations between circadian gene polymorphisms and bipolar I disorder (BPI), as well as schizoaffective disorder (SZA) and schizophrenia (SZ). The results are plausible, based on prior studies of circadian abnormalities. As replications have not been attempted uniformly, we evaluated representative, common polymorphisms in all three disorders.

METHODS

We assayed 276 publicly available 'tag' single nucleotide polymorphisms (SNPs) at 21 circadian genes among 523 patients with BPI, 527 patients with SZ/SZA, and 477 screened adult controls. Detected associations were evaluated in relation to two published genome-wide association studies (GWAS).

RESULTS

Using gene-based tests, suggestive associations were noted between EGR3 and BPI (p = 0.017), and between NPAS2 and SZ/SZA (p = 0.034). Three SNPs were associated with both sets of disorders (NPAS2: rs13025524 and rs11123857; RORB: rs10491929; p < 0.05). None of the associations remained significant following corrections for multiple comparisons. Approximately 15% of the analyzed SNPs overlapped with an independent study that conducted GWAS for BPI; suggestive overlap between the GWAS analyses and ours was noted at ARNTL.

CONCLUSIONS

Several suggestive, novel associations were detected with circadian genes and BPI and SZ/SZA, but the present analyses do not support associations with common polymorphisms that confer risk with odds ratios greater than 1.5. Additional analyses using adequately powered samples are warranted to further evaluate these results.

Investigation of variants in the promoter region of PIK3C3 in schizophrenia

The PIK3C3 gene has been implicated as a candidate gene for schizophrenia by functional evidence and genetic association studies. A series of previous studies have found susceptibility SNPs in promoter region. To further verify its susceptibility to schizophrenia in the Chinese population and the function of the polymorphisms, we performed a case control study in 556 unrelated schizophrenia patients and 563 normal controls as well as an in vitro functional analysis. In our association analysis of-432C-/T, we discovered obvious differences in allele frequency between patients and controls (P=0.017). A T/C haplotype constructed by -432C-/T and -86insC, which are tightly linked with each other (r(2)=1) can significantly weaken promoter's transcriptional activity by 20% (p=0.002 by t-test). Though we cannot exclude the possibility that susceptibility of -432C-/T is caused by its linkage disequilibrium with other causal variants, our results do support PIK3C3 play a significant role in the etiology of schizophrenia.

A different depression: clinical distinctions between bipolar and unipolar depression

Delayed diagnosis or misdiagnosis can prolong the suffering of patients with bipolar disorder. Accurate early diagnosis is sometimes difficult, however, particularly because patients often present in the depressive phase, which can easily be mistaken for unipolar depression. Unfortunately, therapy appropriate for unipolar depression can increase the risk of manic switch or cycle acceleration in bipolar disorder, especially in those with a family history of bipolarity and suicide, although some antidepressants may be useful in some bipolar patients. In addition, most currently available mood stabilizers, though effective in managing mania, do not effectively resolve depression. In contrast, lamotrigine has shown activity in bipolar depression and has a very low risk of manic switch. Bipolar depression, compared with unipolar depression, is more likely to be associated with hypersomnia, motor retardation, mood lability, early onset, and a family history of bipolar disorder. Awareness of these distinctions can greatly improve diagnosis of bipolar disorder and provide an opportunity for effective therapeutic intervention.

Association of neural cell adhesion molecule 1 gene polymorphisms with bipolar affective disorder in Japanese individuals

BACKGROUND

Although the pathogenesis of mood disorders remains unclear, heritable factors have been shown to be involved. Neural cell adhesion molecule 1 (NCAM1) is known to play important roles in cell migration, neurite growth, axonal guidance, and synaptic plasticity. Disturbance of these neurodevelopmental processes is proposed as one etiology for mood disorder. We therefore undertook genetic analysis of NCAM1 in mood disorders.

METHODS

We determined the complete genomic organization of human NCAM1 gene by comparing complementary deoxyribonucleic acid and genomic sequences; mutation screening detected 11 polymorphisms. The genotypic, allelic, and haplotype distributions of these variants were analyzed in unrelated control individuals (n = 357) and patients with bipolar disorder (n = 151) and unipolar disorder (n = 78), all from central Japan.

RESULTS

Three single nucleotide polymorphisms, IVS6+32T>C, IVS7+11G>C and IVS12+21C>A, displayed significant associations with bipolar disorder (for allelic associations, nominal p =.04, p =.02, and p =.004, respectively, all p >.05 after Bonferroni corrections). Furthermore, the haplotype located in a linkage disequilibrium block was strongly associated with bipolar disorder (the p value of the most significant three-marker haplotype is .005).

CONCLUSIONS

Our results suggest that genetic variations in NCAM1 or nearby genes could confer risks associated with bipolar affective disorder in Japanese individuals.

Genetic screening for susceptibility to depression: can we and should we?

OBJECTIVE

To summarize current knowledge about genetic susceptibility to mood disorders and examine ethical and policy issues that will need to be addressed if robustly replicated susceptibility alleles lead to proposals to screen and intervene with persons at increased genetic risk of developing mood disorders.

METHOD

Empirical studies and reviews of the genetics of unipolar and bipolar depression were collected via MEDLINE and psycINFO database searches.

RESULTS

A number of candidate genes for depression have been identified, each of which increases the risk of mood disorders two- or threefold. None of the associations between these alleles and mood disorders have been consistently reported to date.

CONCLUSIONS

Screening the population for genetic susceptibility to mood disorders is unlikely to be a practically useful policy (given plausible assumptions). Until there are effective treatments for persons at increased risk, screening is arguably unethical. Screening within affected families to advise on risks of developing depression would entail screening children and adolescents, raising potentially serious ethical issues of consent and stigmatization. Genetic research on depression should continue under appropriate ethical guidelines that protect the interests of research participants.