Pre-mutation


In trinucleotide repeat disorders, where as the length of the number of trinucleotide repeats increases, so too does the likelihood of further repetitive mutation (a phenomenon called dynamic mutation), the pre-mutation range is the range at which a carrier has enough repeats not to show symptoms of the disease, but such that there is a significant probability of further mutation, putting their offspring at risk.

Although generally pre-mutation carriers are asymptomatic, they may occasionally develop (especially in later life) a disease that is closely related to the disease caused by full mutation. For instance, some men and women with CGG pre-mutation do not have Fragile X Syndrome, but do have Fragile X-associated tremor (or ataxia syndrome), which is characterised by movement difficulties (ataxia), memory loss, peripheral neuropathy (loss of sensation in the extremities) and a range of mental and behavioural changes.