Studies of the DXS7 polymorphism at the MAO loci in unipolar depression

Meta-analyses of genetic studies on major depressive disorder

The genetic basis of major depressive disorder (MDD) has been investigated extensively, but the identification of MDD genes has been hampered by conflicting results from underpowered studies. We review all MDD case-control genetic association studies published before June 2007 and perform meta-analyses for polymorphisms that had been investigated in at least three studies. The study selection and data extraction were performed in duplicate by two independent investigators. The 183 papers that met our criteria studied 393 polymorphisms in 102 genes. Twenty-two polymorphisms (6%) were investigated in at least three studies. Seven polymorphisms had been evaluated in previous meta-analyses, 5 of these had new data available. Hence, we performed meta-analyses for 20 polymorphisms in 18 genes. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Statistically significant associations were found for the APOE varepsilon2 (OR, 0.51), GNB3 825T (OR, 1.38), MTHFR 677T (OR, 1.20), SLC6A4 44 bp Ins/Del S (OR, 1.11) alleles and the SLC6A3 40 bpVNTR 9/10 genotype (OR, 2.06). To date, there is statistically significant evidence for six MDD susceptibility genes (APOE, DRD4, GNB3, MTHFR, SLC6A3 and SLC6A4).

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.

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.

Association of a MAOA gene variant with generalized anxiety disorder, but not with panic disorder or major depression

This study was conducted to detect a possible association of a T941G single nucleotide polymorphism (SNP) in the monoamine oxidase A (MAOA) gene with generalized anxiety disorder (GAD), panic disorder (PD), or major depression (MD). Fifty GAD patients (34 females and 16 males), 38 PD patients (21 females and 17 males), and 108 MD patients (80 females and 28 males) were included. The comparison group consisted of 276 (132 females and 144 males) unrelated healthy individuals. The 941T allele was over-represented in patients suffering from GAD (chi(2) = 6.757; df = 1; P < 0.01, not corrected for multiple testing) when compared to healthy volunteers. No association was observed in MD or PD. This is the first study specifically analyzing the MAOA G941T polymorphism in GAD and thus needs to be replicated in an independent sample. However, the results are in line with previous data suggesting an association between the MAOA locus and regulation of complex human behavior.