Hungtington’s Disease Case Study
Huntington’s disease is an autosomal dominant disorder, meaning anyone with the dominant allele will develop this disease. In Huntington’s disease there is a continuous breakdown of neurons. An individual who has Huntington’s disease has an increased difficulty in their ability to think and move, as well as behavioral issues. The disease is generally diagnosed with genetic testing.
Huntington’s disease is unique in the fact that it does not affect individuals in their early years or prevent them from living past infancy.The symptoms often generally develop later in life, often when a people are in their 30s or 40s. This means that individuals may reproduce and potentially pass on the mutation to their offspring before they are aware they have the disease. There are medications available to help manage the symptoms of Huntington’s disease, but there is not yet a cure.
Huntington’s disease is caused by a mutant huntingtin gene (HTT) where there is a type of mutation called triplet repeats. In Huntington’s disease, there are extra repetitions of the DNA sequence CAG, which encodes glutamine, on chromosome 4. In a normal individual the number of repeats of the CAG sequence is between 9 to 36. The individuals with Huntington’s disease have greater than 37 repeats of the CAG sequence. The larger the number of repeats, the more severe the condition.
Since Huntington’s is autosomal dominant, the individuals who have Huntington’s disease have at least one dominant allele. This means that individuals who are homozygous dominant (HH) and individuals who are heterozygous (Hh) will develop Huntington’s disease. Individuals who do not have Huntington’s disease are homozygous recessive (hh).
Normal = hh (homozygous recessive)
Huntington’s disease = Hh (heterozygous)
Huntington’s disease = HH (homozygous dominant)