Several psychiatric disorders including Schizophrenia, major depressive disorder (MDD), bipolar disorder, attention-deficit/hyperactivity disorder and autism spectrum disorder are all very common. WHO data suggest MDD as a leading cause of adult disability, however the complex nature of the disease etiology makes it least understood among its more studied disease counterparts. Although both genetic and environmental factors are known to contribute substantially to the etiology of MDD, several association studies both single gene and Genome Wide Association Studies (GWAS) are available describing the contribution of multiple genes. Severe lacunae exist in correlation among these association studies that prevent a clear definition in genetic causes that could be a result of small samples, epigenesis, heterozygosity in populations studied, presence of rare variations as well as lack of proper co-relation with environmental factors. With the advances in nucleic acid and amino acid sequencing techniques in this era of genomics and proteomics, the identification of novel disease markers is easier. More extensive study identifying rare variations in larger population along with a more systematic study including system pathways as well as genetic and protein interaction is recommended to obtain a clear picture of the underlying genetic causes of these complex disorders.
Keywords: Biomarkers, Candidate genes, Depression, Epigenetics, Genome Wide Association Studies (GWAS), Genomics, Major depressive disorder (MDD), Pharmacogenetics, psychiatric disorders, Serotonin transporter (5HTT).