A Review on Huntington’s Disease

Huntington’s Disease (HD) is a progressive neurodegenerative disorder that gradually declines cognitive skills, impair memory and normal movements of affected individuals. This disease affects cerebral cortex and basal ganglia of the brain and those parts of the brain which are associated with the memory retention and motor movement. HD is an autosomal dominant inherited disease caused by the elongation of CAG repeats on the short arm of chromosome 4 at 4p16.3 in huntingtin gene (Htt gene). The mechanisms by which mutant Htt (mHtt) gene causes HD have not been known yet, however mHtt gene can impair mitochondrial function by deregulation of transcriptional processes, calcium imbalance and defective mitochondrial bioenergetics. mHtt gene of neurons affected by HD induces intracellular Ca2+ which enters in the mitochondria and opens the mitochondrial permeability transition pores (mPTP), leading to decrease in mitochondrial ATP, and neuronal cell death. The mean age of onset of this disease is 40 years but the earlier onset of the disease in childhood is known as Juvenile onset HD. HD is characterized by the motor symptoms, cognitive symptoms and psychiatric symptoms. This disease is diagnosed on the basis of symptoms found in the affected individuals and confirmation is done by the genetic testing in which CAG repeats are counted. When the CAG repeat is 40 and above, then the individual is said to be suffering from this disease.