The prevalence in the United States is estimated to be 4.1 to 8.4 per 100,000 people. The frequency varies in other countries.  In most of Europe, the prevalence ranges from 1.63 to 9.95 per 100,000 people. In Finland and Japan, the prevalence is less than 1 per 100,000 people.  There are other regions with an unusually high prevalence: Lake Maracaibo in Venezuela (700 per 100,000 people), Mauritius Island in Africa (46 per 100,000), and Tasmania Island in Australia (17.4 per 100,000).

Huntington's disease is an inherited disorder. It is caused by an alteration in the HHT gene. People receive two copies of most genes; one received from the mother and one from the father. Hungtington diseaseIt is an autosomal dominant disorder; meaning that if only one copy of the gene is altered, that is enough to cause the disease.

The HTT gene at chromosome 4 is responsible for building the protein called hungtingtin. The exact function of this protein is unclear, but it is thought to play a role in brain cell function. A segment of the hungtingtin protein consisting of the amino acid glutamine, denoted by the genetic code CAG, typically repeats approximately 10 to 35 times. Huntington's Disease is caused by mutations or changes on the HTT gene that causes this segment to repeat over 35 times. The segment is repeated so many times that it creates an extremely long hungtingtin protein.  The protein segments have a “glue effect”, sticking together and causing “aggregates”. The “aggregates” cause the disease symptoms to manifest because it causes the brain cells to function abnormally and eventually die. How these “aggregates” trigger the death of brain cells are unclear, but the “aggregates” and the number of CAG segment repeats are inversely correlated to the age of onset.  Meaning, the more “aggregates” and CAG segment repeats there are, the earlier the onset of the disease. The onset is typically around age 35 to 44. There are reports of cases ranging from age 2 to 80. Environmental factors and other genes can influence the age of onset.

Symptoms typically develop around age 35 to 44 but can appear as early as age 2, or as late as age 80. Patients can experience uncontrolled movements (chorea) in the arms, legs, head, and face. There is a progressive decline in memory, thinking, reasoning, concentration, judgement, and organization. There is an increase in irritability, anxiety, depression, anger, and obsessive-compulsive behavior, which causes repetitive questions and movements. Mood alterations and behavioral changes are common.  The increase in stress can lead to heart disease and the increase in depression may lead to suicidal thoughts. As the symptoms develop, they may worsen over the next 10 to 25 years. Patients may develop slurred speech, difficulty swallowing, and significant weight loss, possibly leading to choking, respiratory, and gastrointestinal problems.

There is a juvenile form of the disorder that develops around in children or teen-agers. Symptoms can include involuntary muscle movements, slowness of movements, and clumsiness. There are also changes in behavior and the ability to think clearly. There may also be stiffness of the legs, seizures, and swallowing or speech difficulties. The onset of these symptoms is slow and the progression can vary among affected individuals. Generally, there is a family history of Huntington´s disease in people with the juvenile form.

In 1993, the HTT gene was identified. Genetic testing is now available to confirm the affected gene for the hungtingtin protein in individuals that suspect Huntington's disease or individuals who are at risk because a parent has the disease. There is debate as to whether people at risk for this disorder should be tested if symptoms aren’t present. Because there is no effective treatment, some people choose not to be tested until symptoms become apparent.

The Huntington’s Disease Society of America (HDSA) recommends at-risk individuals to find a genetic testing center that follows the HDSA testing guidelines. These centers have experts in Huntington´s disease and many local offices. It is highly recommended to receive genetic counseling before and after genetic testing. Results of genetic testing can take several weeks. Genetic testing is not recommended for individuals under age 18.  Children can have juvenile onset of Huntington´s disease and can be diagnosed with a neurological (brain) exam. You can find more information at hdsa.org.

Currently, there is no treatment to stop or reverse the disease. Treatment focuses on managing the symptoms. Different types of medications can be prescribed to treat movements, mood stability, depression, and anxiety. For example, antipsychotic drugs can help with moods and movements. There is a drug called tetrabenazine which is specifically indicated for involuntary movements in Huntington's disease. Antidepressants, anti-anxiety medications, and insomnia drugs are used as well.

Huntington's disease can cause disability and fatality. The disease usually runs its full course in 10 to 30 years. The earlier the disease appears, the faster it progresses. The disease itself is not fatal, but other life-threatening complications related to the disease can be fatal. Pneumonia and heart disease are the leading two causes of death in affected individuals. There are high risks of falling and choking. Suicides, respiratory complications and gastrointestinal diseases (such as pancreatic cancer) are common as well. The overall physical, emotional, and mental stresses cause the body to weaken and makes it more difficult to fight off diseases. To prolong life, it is recommended to use extra care when eating, this can prevent choking and aspiration pneumonia. Exercising and sleeping in an elevated position can prevent respiratory infections. Healthy diet can decrease risk for heart diseases.

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Jimenez-Sanchez, M., et al. (2017). "Huntington's Disease: Mechanisms of Pathogenesis and Therapeutic Strategies." Cold Spring Harb Perspect Med 7(7).

Jodeiri Farshbaf, M. and K. Ghaedi (2017). "Huntington's Disease and Mitochondria." Neurotox Res 32(3): 518-529.

Hutington disease – Medscape eMedicine

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