The link between this protein and the selective loss of neuronal groups in the CNS remains to be established. HD is found in all ethnic groups. Males and females are diagnosed in equal numbers. Symptoms arising from a typical presentation of HD usually do not develop until a person is aged 35 years or older. By the time of diagnosis, many patients already have had children and have passed the gene to another generation.
Muscular rigidity is more common with juvenile-onset illness.
Between one half and three fourths of patients affected by HD present with primary complaints of involuntary movements or rigidity. In the remainder of cases, the primary presentation is one of early mental status changes that initially appear as increased irritability, moodiness, or antisocial behavior. Classic choreiform movements begin as a piano-playing motion of the fingers or as facial grimaces. As the disorder advances and involves the trunk, a characteristic dancing gait evolves. Although patients appear to be off-balance, the ability to balance is actually well preserved.