Ten years later, an international collaborative group called the Gene Hunters, organized by the Hereditary Disease Foundation, finally isolated and sequenced the mutant huntingtin gene.11 Once the gene was isolated, it could be inserted into a worm, a fly, or a mouse to see how the disease would progress. The Gene Hunters noticed that one portion of the huntingtin gene is larger than normal. This portion is called a CAG expansion, and it is what causes the disease.
