Ataxia: Triplet Repeat Diseases

As can be seen from the table, many of the ataxias are due to expansion of a three-nucleotide repeated region in a gene. CAG, coding for glutamine, is the most common, but others occur as well.

Disease onset and severity are correlated with repeat length, with longer repeats causing early onset and more severe disease.

Expanded repeats are often unstable during DNA replication. Growth of the repeat is common. This causes the phenomenon known as anticipation, or earlier onset in succeeding generations. For instance, onset might be at age 50 in a parent, but age 30 in a child.

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