Huntington's syndrome is one of the most terrible genetic diseases. Its signs include the development of
chorea (involuntary jerks of the face or limbs and the gradual loss of thought processing) and
dementia, the loss of learned abilities. There may be memory loss, and those infected even start to lose the ability of
abstract thought and judgment; Disorientation is also very common, as are personality changes.
Signs begin at the 40-50 year age, but onset varies from around 20 to 80. But it gets worse.
It's a dominant gene.
That's right- if one of your parents has it, you've got a 50% chance of picking it up. But, if you have two parents with Huntingtons, you therefore have a 75% chance of picking it up.
The gene responsible for Huntington's is called IT15, is located on the fourth chromosome. It regulates production of a protein known as huntingtin, found in neurons throughout the brain. Mutations of the IT15 gene result in abnormally long repeats of DNA instructions. These instructions include unusual, repeated sequences of certain basic chemicals (cytosine, adenine, and guanine or CAG trinucleotide) repatition. These expanded CAG sequences result in the production of abnormal huntingtin protein.
Some with Huntington's develop symptoms before age 20. Initial signs have been reported before puberty, or even in children as young as four.
Known as Juvenile Huntington's, loss of mental skills happens at the same time as increasing muscle stiffness and slowing of movements- although this most commonly comes in juvenile cases, the rigid form of the disease has also been reported in some adults.
The worst thing is, the treatment of H.D. doesn't slow, alter, or reverse the disease's effects. Careful attention to changes in a patient's condition may help to prevent certain effects and improve quality of life.
Note that if a child inherits 2 copies of the gene, it has no IT15 and will almost certainly die in the womb or very soon after.