Genetics play a key role in the causation, development and heritability of many forms of diseases and disorders (Reece, 2011). Unfortunately, advancements in studies relating genomics to psychiatric illnesses have been slow in the past. This is due to the difficulty in identifying genes that contribute to such diseases. However, recent studies on a particular gene have revealed its connection with numerous psychiatric illnesses including ADHD, schizophrenia and autism (Ross RG, 2012).
The genetic component of diseases is associated with mutations of the gene which may induce an effect on the risk of developing illnesses (Reece, 2011). In the case of common non-psychiatric diseases, the risk of developing them can be linked to common variations of a few mutated genes that can be thoroughly analysed (which it has been). However, in the case of psychiatric diseases, it is a different story. A genome-wide association study (International Schizophrenia Consortium et al, 2009) produced novel results suggesting that psychiatric disorders are potentially affected by not a few, but thousands of gene variants, each having only a minute contribution to the disorder.
So how do researchers determine what genes are associated with psychiatric disorders if each gene has only a small effect? The method involves examining large alterations in the DNA nucleotide sequences which are replicated throughout the genome. These large alterations consist of DNA segments that are either missing or duplicated in the sequence. Because the number of altered segments varies as DNA is replicated, the genes are termed copy number variants (Henrichsen CN, 2009).
As genes are involved with many molecular activities such as protein synthesis, studying copy number variants (mutations in genes) is made simpler by recognising abnormal genetic activity.
Research conducted by Williams et al (2012) on 896 children with ADHD showed that the genome of those affected by ADHD exhibited a greater amount of copy number variants. Among the duplications of altered genes was the CHRNA7 gene, which encodes α7 nicotinic receptors. These receptors are crucial in the nervous system and are involved in many mental functions (Mazurov, 2006). Therefore, duplications of the CHRNA7 gene affects α7 nicotinic receptors, which in turn affect cognitive functions and ultimately lead to increased risk of ADHD, schizophrenia and possibly many other psychiatric illnesses.
This association was further reinforced as four subsequent studies of subjects from the United Kingdom, United States and Canada all demonstrated similiar results – the amount of duplications of CHRNA7 and other copy number variants was greater in the genomes of those affected by ADHD (Williams et al, 2012).
Although the results of current studies (International Schizophrenia Consortium et al and Williams et al) do not have major contributions towards pharmaceutical or therapeutical developments, they are nevertheless fundamental and crucial to successive research. And the hope is that the findings of genetic information will lead to further studies in identifying more genes involved in and developing medicinal solutions for treating psychiatric illnesses.
Boone, PH, Wiszniewski, W, Lupski, JR 2011, ‘Genomic medicine and neurological disease’, Human Genetics, vol. 130, no. 1, pp. 103-121.
Henrichsen, C, Chaignat, E, Reymond, A 2009. ‘Copy number variants, diseases and gene expression’, Human Molecular Genetics, vol. 18, review issue 1, pp. R1-R8.
International Schizophrenia Consortium, Purcell, SM, Wray, NR, Stone, JL, Visscher, PM, O’Donovan, MC, Sullivan, PF, Sklar, P 2009. ‘Common polygenic variation contributes to risk of schizophrenia and bipolar disorder’, Nature, vol. 460, pp. 748-752.
Mazurov, A, Hauser, T, Miller, CH 2006, ‘Selective α7 Nicotinic Acetylcholine Receptor Ligands’, Current Medicinal Chemistry, vol. 13, no. 13, pp. 1567-1584.
Reece, JB et al 2011, Campbell Biology, 9th edn, Pearson Benjamin Cummings, San Francisco.
Ross, RG 2012, ‘Advances in the Genetics of ADHD’, The American Journal of Psychiatry, vol. 169, no. 2, pp. 115-117.
Williams, NM et al 2012, ‘Genome-Wide Analysis of Copy Number Variants in Attention Deficit Hyperactivity Disorder”: The Role of Rare Variants and Duplications at 15q13.3’, The American Journal of Psychiatry, vol. 169, no.2.