Friday, 25 May 2012

Gene Linkages To Major Depressive Order

After extensive linkage analyses conducted by scientists on families of sibling pairs affected by recurrent depression, positive results have indicated gene linkages to the psychological disorder (The American Journal of Psychiatry 2010). Major depressive disorder has been listed by the American Journal of Psychiatry as the leading cause of disability and severe cases of depression are difficult to treat due to external factors such as stress, loss or trauma that contribute to fifty percent of cases (Centre for Mental Health Services 1996). While external factors are seen to be the major cause of depression, the magnitude of genetic influence on the disorder is equally concerning, contributing to over forty percent of cases of major depressive disorder (Levison & Nichols 2012).

Logically, the risk of an identical twin inheriting major depressive disorder is far greater than that of a non-identical twin, considering that identical twins share one hundred percent of their genes while non-identical twins share half of that percent (Levison & Nichols 2012). Over a span of ten years, King’s College in London carried their research on a large sibling pair sample of 971 identical twins that were suffering severe depression. Of the 971 affected sibling pairs in the 839 families, analysis showed that instances of genetic variations in the regions of chromosome 3p25-26 were constant within these patients. These findings also matched data that was obtained by Washington University in St. Louis, who had also led a study using a smaller sample consisting of 200 families. The regions of chromosome 3p25-26 contain forty other genes, implicating that any of those genes could be a possible contributor to major depressive disorder, and that broader investigations would be necessitated. (King’s College London 2011).

Figure 1: Significant loss of neurotransmitter activity in a depressed individual's brain compared to a recovered brain
 Makkar,J. 2010, Depression (Depression, Mania, Bipolar Disorder), Punjab Info, Kharar

Gathered from both studies, gene GRM7 was found within chromosome region 3, a gene responsible for encoding a major neurotransmitter in the central nervous system, metabotropic glutamate receptor 7 (mGlur7) (National Centre for Biotechnology Information 2011). Gene GRM7 is concerned with features specific to normal brain function, and is widely expressed in regions of the cerebral cortex, hippocampus and the cerebellum. Mutations of this gene have been an underlying cause for other psychological disorders such as bipolar and schizophrenia (Bly 2010).

With the discovery of chromosome 3p25-26 scientists are now able to locate explicit genes in order to design specific treatments that will effectively alleviate depression. While scientists have yet to isolate one or several of the forty genes within chromosome 3p25-26, the discovery of this gene linkage will hopefully set a solid platform in place for future success in developing treatments for severely depressed patients (King’s College London 2011).

The American Journal of Psychiatry 2010, Genome-Wide Association Study of Major Recurrent Depression in the U.K. Population, viewed 17 March 2010,  <>
Bly, M. 2010, Mutation in the metabotropic glutamate receptor gene, GRM7, associated with schizophrenia and bipolar disorder, Mental Health Research Institute, viewed 17 March 2012,
King’s College London 2011, Scientists find genetic link to depression, viewed 15 March 2012, <>
Levison, D. & Nichols, W. 2012, Major depression and genetics, Stanford School of Medicine, viewed 15 March 2012,
National Centre for Biotechnology Information 2011, GRM7 glutamate receptor, metabotropic 7, viewed 15 March 2012,


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