A member asked:

How much earlier than my mom will i get huntingtons disease? ive read that symptoms start earlier in each generation because of the way the defective gene repeats. but how much earlier? my mom didnt have symptoms until she was over 50. im only 23, but

A doctor has provided 1 answer
Dr. Herbert Krob answered

Specializes in Neurology

Huntington's disease is a complicated neurodegenerative disorder that can cause involuntary writhing, dance-like movements of the limbs, other abnormal movements, personality changes and psychiatric symptoms, heart disease and other problems. It is an uncommon condition (about 5-10 cases per 100000 people). Huntington's disease is caused by a mutation in the huntingtin gene. Inside this gene is a stretch of dna that consists of repeating sequences the genetic code letters, or nucelotides, c, a, and g. These three nucleotides can be repeated (cagcagcag...) dozens of times. The number of "trinucleotide repeats" seems to determine if and when the disease will make itself known. People with less than 28 repeats are normal. People with 28 to 35 repeats are "intermediate". People with 35 to 40 repeats may or may not develop huntington's disease. People with more than 40 repeats will usually be affected, and the higher the number of repeats, the earlier the disease starts. Trinucleotide repeat diseases like huntington's disease (there are others), are characterized by a property called "anticipation." anticipation means that children of people with huntington's often develop the disease at an earlier age than their parents did. This was first noticed even before anything was known about trinucleotide repeats. After the repeats were discovered, it was found that children had more repeats than their parents. The number of repeats tends to increase more if the father carried the abnormal gene that if the mother did. It is not possible to pinpoint when exactly someone might develop huntington's disease based on when their affected parent developed the disease. Genetic testing may be helpful to identify the number of trinucleotide repeats that someone carries, but presymptomatic testing is declined by the majority of children of people with huntington's disease.

Answered Oct 3, 2016



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