Huntington's disease is an inherited disorder caused by a genetic defect on chromosome 4. The origin is a CAG expansion that causes that the allele expanded cannot be transcribed and produces no protein. Thus, these patients present only half of Huntington protein in their cells.
As the gene is passed from parent to a child, regardless of gender, the number of repeats tends to be bigger. The greater the number of repeats, the greater the chance of developing symptoms at an earlier age. Therefore, as the disease is passed from parents to children, symptoms develop at younger and younger ages.
There are two forms of Huntington's disease:
The genetic test examines the expansion size by quantifying the number of CAG triplets using PCR.
Typically, this region of DNA is repeated 10 to 26 times, but a person with Huntington's disease can present more than 36 repeats.
The test is particularly aimed at those who, for medical reasons, require a confirmatory genetic diagnostic of Huntington disease.
It is also indicated for people who have no symptoms, adults with family history of Huntington's disease, and wish to know whether they carry the mutated allele. For ethical reasons it is not advisable to make the diagnostic of carriers in asymptomatic family members who are minors.
Huntington disease causes disability that gets worse over time. It is important to know that the disease affects everyone differently. The number of CAG repeats of this gene can determine the severity of symptoms.
People with few repeats may have mild abnormal movements later in life and slow progression of the disease, while those with a greater number of repeats can be severely affected at an early age.
Currently, the goal of treatment is to reduce symptoms and help the person to fend for themselves for as long and as comfortable as possible.