Tuesday, 22 May 2012

Genetic Testing For Huntington’s Disease

Advances in genetic research have made it possible for patients to be tested for hereditary diseases they may be at risk of developing, due to their family history. The condition Huntington’s Disease, is one such hereditary disorder which can be discovered relatively early in a patient’s life by means of genetic testing (Muthane, 2010). However, as Huntington’s is degenerative and has with no known treatment; ethical questions are raised when deciding whether or not an at risk person should be tested  early on in life (Muthane, 2010). Huntington’s Disease is a genetic condition, meaning that a carrier of the gene had it passed down to them from their parents meaning they have carried the gene their entire lives. (Youseff, 2011)

 It is an extremely rare condition with an estimated 0.003-0.007% of people a carrier of the mutant gene.  However, it is a terminal illness, resulting in low quality life and inevitable death of the patient within 10-30 years (GHR, 2012). The various psychiatric problems and other symptoms such as memory loss and impulsiveness do not become apparent until middle age. After onset the disease degenerates and other symptoms such as involuntary muscle movements, muscle rigidity and spasms set in (GHR, 2012). This means the patient has constant trouble with walking and communicating, making it impossible for them to live out a ‘normal life’. In Huntington’s disease, mutated proteins change the transcription process, meaning key protein’s needed to maintain the cell are not produced. This causes cell death which in turn brings forth the symptoms associated with the disease. (Youseff, 2011)

Advances in genetic research have made it possible for Huntington’s to be detected by means of genetic testing. People with the condition carry a mutant gene HTT gene. When this gene is mutated it has a greater than normal CAG repeat on that particular gene (Muthane, 2010). A CAG repeat is when the nucleotides; cytosine, adenine and guanine repeat to form a specific gene.  The greater the CAG repeat on the HTT gene is, the higher the risk is that a patient will develop Huntington’s. The HTT gene of a non-carrier will have less than 26 CAG repeats whereas someone who has greater than 40 CAG repeats will inevitably develop the disease (CUMC, 2009). A higher number of repeats has also been associated with age of onset of the disease. Thus, the aforementioned advances in genetic testing now allow us to find the number of CAG repeats on the HTT gene. If a person tests positive for Huntington’s disease, the excess CAG repeats cause an error in transcription which in turn causes cell death (Youseff, 2011).

Advances in genetic testing have allowed for conditions as Huntington’s to be tested for from any age, before symptoms set in. Although Huntington’s is an incurable condition, steps may be taken in order to slow the progress of the disease (Muthane, 2010), making genetic testing important for anyone who may be at risk.

By Angus Douglas

Reference List
Columbia University Medical Center (CUMC), (2009)
Genetic Testing For Huntington’s Disease

 Muthane. U (2010)
Predictive Genetic Testing In Huntington’s Disease

Youseff. S (2011)
Huntington’s Disease: From Mutant Huntington Protein to Neurotropic Factor Therapy

Genetics Home Reference (GHR), (2012)
Huntington’s Disease

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