Other cases in South Africa, Venezuela, and Tasmania have also been traced to ancestors from Europe. Spontaneous mutations outside of this common source are felt to be rare or nonexistent. The past 10 years have seen significant breakthroughs in our understanding of the pathogenesis and genetics of this incurable and fatal disease. The most common presenting feature is personality change. Patients may manifest apathy, loss of personal hygiene, impaired judgment, and inappropriate or antisocial behavior.
Psychiatric disturbances are common.
Another quarter of patients have evidence of psychosis marked by delusions and hallucinations. Although usually occurring shortly after the onset of movement disorder, the dementia syndrome of HD may precede chorea by several years. Early cognitive impairments include word-finding difficulty as well as recent and remote amnesia. Fluent aphasia, agnosia, and apraxia, typical of Alzheimer's disease, are usually absent. As the disease progresses, frontal lobe deficits become prominent including impaired judgment, concentration, planning, and sequencing abilities.