Huntington's Disease Home Page

The HTT Gene

     Huntington's Disease is caused by a mutation in the HTT Gene. The official name of this gene is "Huntington" and HTT is the official symbol. This gene codes instruction for making a protein called 'Huntington'. The function of this protein is unknown, but by studying the symptoms of this disease, it is believed that it plays an important role of neurons, which is a nerve cell in the brain. The DNA sequence that causes the mutation is a CAG Trinucleotide Repeat.

    This gene is essential for normal development before birth, and is found in many of the bodies tissues. The highest level of activity, though, is in the brain. This gene may be involved in chemical signaling, transporting materials, attaching (binding) to proteins and other structures, and protecting the cell from self-destruction (apoptosis).^[1]

How it's Inherited

     You only need one copy of the gene to inherit the disease, though in very rare cases an individual can develop Huntington's although neither of their parents are infected. Also, as this gene is passed from one generation to the next, the size of the repeat often increases.

     The segment is normally repeated around 10-35 times, but in those with Huntington's it repeats 36 to more than 120 times. People with 36-40 repeats may not develop the symptoms of the disease, but those with more than 40 almost always develop it. A larger number of repeats is usually linked with an earlier onset of the disease. People with the Adult-Onset form of the disease have 40-50 repeats. Those with the Early-Onset form often have more than 60 repeats.^[2]