Huntington’s disease:
Huntington's disease is a progressive brain disorder caused by a single defective gene on chromosome 4 — one of the 23 human chromosomes that carry a person’s entire genetic code.
This defect is "dominant," meaning that anyone who inherits it from a parent with Huntington's will eventually develop the disease. The disorder is named for George Huntington, the physician who first described it in the late 1800s.
The defective gene codes the blueprint for a protein called huntingtin. This protein's normal function isn't yet known, but it's called "huntingtin" because scientists identified its defective form as the cause of Huntington's disease. Defective huntingtin protein leads to brain changes that cause abnormal involuntary movements, a severe decline in thinking and reasoning skills, and irritability, depression and other mood changes.
Symptoms
Symptoms of Huntington's disease usually develop between ages 30 and 50, but they can appear as early as age 2 or as late as 80. The hallmark symptom of Huntington's disease is uncontrolled movement of the arms, legs, head, face and upper body. Huntington's disease also causes a decline in thinking and reasoning skills, including memory, concentration, judgment and ability to plan and organize.
Huntington's disease brain changes lead to alterations in mood, especially depression, anxiety, and uncharacteristic anger and irritability. Another common symptom is obsessive-compulsive behavior, leading a person to repeat the same question or activity over and over.
Causes and risks
The defective gene identified in 1993 causes virtually all Huntington’s disease.
The huntingtin gene defect involves extra repeats of one specific chemical code in one small section of chromosome 4. The normal huntingtin gene includes 17 to 20 repetitions of this code among its total of more than 3,100 codes. The defect that causes Huntington's