The mutation of one single gene causes the disease. The mutated gene may come from the father, the mother or the mutation may be new (de novo mutation). The mutations causing cerebellar ataxias are often of a special type: the size of the gene is increased by the repeat of a codon that codes for the amino-acid glutamine. As a consequence, the coded protein contains an abnormally long sequence of repeated glutamine.
This particular type of mutation is commonly associated with an abnormal structure (an "inclusion") that is located in the nucleus of some neurons and that contains all the abnormal protein or only part of it. The role of these inclusions in the mechanism of the disease is discussed: they could be toxic or protective. Their study in humans and animal models is very active.