HUNTINGTON'S DISEASE (HD)

Huntington's disease (HD) is a neurodegenerative genetic disorder that affects muscle coordination and leads tomental decline and behavioral symptoms. The most characteristic initial physical symptoms are jerky, random, and uncontrollable movements called chorea. Chorea may be initially exhibited as general restlessness, small unintentionally initiated or uncompleted motions, lack of coordination, or slowed saccadic eye movements. These minor motor abnormalities usually precede more obvious signs of motor dysfunction by at least three years. The clear appearance of symptoms such as rigidity, writhing motions or abnormal posturing appear as the disorder progresses. These are signs that the system in the brain that is responsible for movement has been affected. Psychomotor functions become increasingly impaired, such that any action that requires muscle control is affected. Common consequences are physical instability, abnormal facial expression, and difficulties chewing, swallowing, and speaking. Eating difficulties commonly cause weight loss and may lead to malnutrition. Sleep disturbances are also associated symptoms. Juvenile HD differs from these symptoms in that it generally progresses faster and chorea is exhibited briefly, if at all, with rigidity being the dominant symptom. Seizures are also a common symptom of this form of HD.

Huntington's disease is autosomal dominant, meaning that an affected individual typically inherits one copy of the gene with the mutant allele from an affected parent. Since penetrance of the mutation is very high, those who have a mutated copy of the gene will have the disease. In this type of inheritance pattern, each offspring of an affected individual has a 50% risk of inheriting the mutant allele and therefore being affected with the disorder. All humans have two copies of the Huntington gene (HTT). This gene allows for the production of the Htt protein, but when a trinucleotide repeat expansion occurs in the Htt gene this results in the production of mutant Htt protein. This protein change increases the rate of neural cell death in select areas of the brain, affecting certain neurological functions. The loss of the neurons is not fatal but complications caused by the symptoms shorten life expectancy for the patient.

This assay determines the CAG repeats in the HTT gene using PCR, fragment analysis and southern blot techniques. A trinucleotide CAG repeat expansion greater than 39 repeats is the only known pathogenic variant. In general, normal HTT alleles have a range of less than 26 CAG repeats. Intermediate alleles range from 27-35 CAG repeats. Full mutations of the HTT gene have over 39 CAG repeats.

CPT Code: 81271

Specimen Requirements: 2-5 mL Blood- EDTA tube (Lavender Top)

For Buccal Swab or Saliva samples please contact the lab to obtain a collection kit.

Turn-around-time: 28 days

Disease Specific DNA Test Order Form