Huntington's chorea pedigree, constructed from

restriction fragment length polymorphism (RFLP) studies. The RFLPs show the typical tirplet repeat expansion associated with the defective gene on chromosome 4. Symptoms include degeneration of the brain which becomes obvious between the ages of 40 and 50, accompaned by involuntary movements, behavioural problems, chronic fatigue, apathy, poor memory and progressive dementia.