Thursday, 23 August 2012

Common genetic contribution to mental illnesses

‘Common genetic contribution to mental illnesses’

Viewed throughout history as ‘crazy’ or ‘possessed’, sufferers of both bipolar and schizophrenia will be happy to hear about the exciting new development in locating the cause of these debilitating mental illnesses. Recent research has shown that the same genetic variation occurs in people with one of or both of these conditions.

Bipolar Disorder, a frequently inherited mood disorder characterized by manic highs and depressive lows, has been found to be genetically linked to schizophrenia, a brain disorder with symptoms including persistent delusions, hallucinations and cognitive problems[1]. Recent research has revealed that not only are these brain disorders a result of defective genetics, but the same defective DNA.

Professor Philip Mitchell, senior researcher at Black Dog Institute, has been investigating the genetics of mental illness and brain function. His research group is particularly interesting in bipolar disorder, which they have found to have a strong genetic component, but unlike most other genetic disorders bipolar has been found to arise from “subtle variants in dozens, maybe even thousands of genes” as opposed to just one (as with most genetic defects)1.

These genetic defects or single nucleotide polymorphisms (SNPs – pronounced ‘snips’) are small genetic variations occurring in the genetic coding of someone’s DNA sequence[2].  Chromosomes are the ‘gene-carriers’ of the human body and scientists are able to separate specific genes using dyes. When chromosomes are replicated during meiosis errors or damaging agents (eg radiation) can cause a chromosome to break, usually leading to a SNP. SNPs can be the deletion, duplication, inversion, or translocation of a chromosome fragment[3].

Professor Mitchell’s recent study consisted of 12,000 patients and 52,000 controls, making it ‘the largest ever study of this condition’. His ground-breaking research confirmed that “a gene for a component of the calcium channel (CACNA1C) is involved in causing bipolar disorder”, while it also “identified a novel gene involved in cell surface signaling (ODZ4)”1. When the bipolar disorder and schizophrenia research groups were combined evidence showed confirmed a genetic overlap between these two disorders, with the discovery that CACNA1C was related to the prevalence of both conditions1.
CACNA1C is a gene that belongs to a collection or ‘family’ of genes that provide instructions for making calcium channels; these channels transport calcium ions to generate and transmit electrical signals in a cell. Cellular functions such as cell-to-cell communication, muscle contraction, and the regulation of certain genes all involve calcium ions[4].

A human genome is made up of approximately 3.4 billion base pairs[5], making for very lengthy and difficult research tasks which were impossible until recent technological advancements. Recent findings of combined research groups have identified five new loci for the schizophrenia ‘gene’, giving us seven loci in total[6]. The Psychiatric GWAS Consortium Bipolar Disorder Working Group, a large-scale genome-wide association, has identified a new susceptibility locus near ODZ4[7]. This particular research group was able to identify subunits of calcium channels enriched in bipolar disorder (and in some cases, schizophrenia) association intervals, and that by increasing sample sizes will help to confirm many additional loci5.

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