Huntington’s disease is an inherited autosomal dominant condition that destroys neurons in areas of the brain involved in movement, intellect, and emotions. The effects of Huntington’s include a jerking involuntary movement of the limbs, progressive loss of mental abilities, and the development of psychiatric problems. As it is an autosomal dominant condition, one copy of the altered gene in each cell is sufficient to cause the disorder and therefore an affected person usually inherits the mutated gene from one affected parent.
The mutation which causes Huntington’s disease involves a DNA segment known as a CAG trinucleotide repeat made up of cytosine, adenine and guanine that is normally repeated 10 to 35 times within the gene. In people with Huntington’s disease, the CAG segment is repeated between 36 and more than 120 times, which leads to the production of an unusually long version of the huntingtin protein. Small, toxic fragments of this elongated protein bind together and accumulate in neurons, disrupting the normal function of the cells. As the size of the CAG trinucleotide repeat increases, there is an earlier onset of signs and symptoms, this can result in juvenile (rigid) Huntington’s.
The progression of Huntington’s is divided into five stages based upon the patient’s total score on the total functional capacity (TFC) scale, which is defined by levels of function in workplace, domestic chores, daily activities and level of care required. The Unified Huntington’s Disease Rating Scale (UHDRS) is also used to assess four areas of clinical performance and capacity: motor function, cognitive function, behavioural abnormalities, and functional capacity. Those with the most severe symptoms will give the highest ratings. The Epiomic™ database sub-divides the patient population by both the TFC scale and UHDRS scale, along with the main symptoms which require treatment (e.g anxiety disorders) to give a complete picture of a disease which is currently incurable. Two continuous distributions have been included for this disease within the database: CAG repeat length and patient level of independence (score) providing unique information about the patient population.
Did you know ... Huntington’s disease is estimated to have a much lower prevalence in Japan, China, Finland and Africa.