New reference material helps improve diagnosis of Huntington's Disease

A new 'standard reference material' (SRM) from the National Institute of Standards and Technology (NIST) will help clinical genetics labs accurately diagnose Huntington's disease, an inherited degenerative brain disorder that usually begins between ages 35 and 50 and progressively leads to physical impairment, dementia and death.

 
Excessive repetitions of the cytosine-adenine-guanine (CAG) nucleotide sequence in a gene from a Huntington's disease patient (bottom) compared to a gene from a person without the neurodegenerative disorder (top) Credit: National Institute of General Medical Sciences, National Institutes of Health

A person whose mother or father developed Huntington's disease has a 50-50 chance of getting the currently incurable disease.

Huntington's disease results from a genetic mutation affecting approximately one in 10,000 persons. The mutation is characterised by an excessive number of repeats of a sequence of three nucleotides (the chemical building blocks of DNA), cytosine-adenine-guanine (CAG), located on the fourth of the 23 pairs of chromosomes found in every human cell.

Since 1993, a genetic test has been available to count the number of CAG ''triplet repeats'' that exist, determining if a person will develop Huntington's disease, and if so, how severe it will be.

Individuals with up to 26 repeats are normal. Individuals with 27 to 35 repeats also are unaffected, but the number of repeats can increase in their children. Individuals with 36 to 39 repeats may or may not develop symptoms of Huntington's disease; however, if they do, it will likely be at a much later onset and slower progression than more pronounced cases. Individuals with 40 or more repeats will definitely be affected, while individuals with 60 or more repeats will develop symptoms in childhood.

Electing to be tested for Huntington's disease is an extremely difficult choice. Since a positive diagnosis undoubtedly will affect decisions about careers, relationships, having children and other life events, there is no room for error.