Huntingtin, illustration. Huntingtin is a highly important transcription factor in humans. It is involved in axonal transport and is highly expressed in the brain and testes. Further functions are, at this time, not well understood. Mutations of Huntingtin are the cause of Huntington's disease (HD). Huntington's disease is an illness that affects 10 out of every 100,000 people worldwide. This disorder causes complex cognitive and psychiatric defects, which includes planning, cognitive flexibility, and abstract thinking. As the disease progresses, memory deficits tend to appear. On a molecular level, HD is caused by an expanded repeat in the Huntingtin gene, which encodes an abnormally long polyglutamine repeat. The abnormal proteins exhibit an extended helix.