Huntington's disease is a genetic time bomb: Programmed in the genes, it appears at a predictable age in adulthood, causing a progressive decline in mental and neurological function and finally death.
There is, to date, no cure. Huntington's, and a number of diseases like it, collectively known as trinucleotide repeat diseases, are caused by an unusual genetic mutation: A three-letter piece of gene code is repeated over and over in one gene. Scientists at the Weizmann Institute have now proposed a mechanism that provides an explanation for the remarkable precision of the time bomb in these diseases. This explanation may, in the future, point researchers in the direction of a possible prevention or cure.
The number of repeats in Huntington's patients ranges from 40 to over 70. Scientists have noted that, like clockwork, one can predict by how many times the sequence repeats in a patient's gene both the age at which the disease will appear and how quickly the disease will progress. The basic assumption has been that the protein fragment containing the amino acid (glutamine) encoded in the repeating triplet slowly builds up in the cells until eventually reaching toxic levels. This theory, unfortunately, fails to explain some of the clinical data. For instance, it doesn't explain why patients with two copies of the Huntington's gene don't exhibit symptoms earlier than those with a single copy. Plus, glutamine is produced in only some trinucleotide diseases, whereas the correlation between sequence length and onset age follows the same general curve in all of them, implying a common mechanism not tied to glutamine.