Friedreich's ataxia (FRDA) is a common hereditary degenerative neuro-muscular disorder caused by expansions of the (GAA)n repeat in the first intron of the frataxin gene. The expanded repeats from parents frequently undergo further significant length changes as they are passed on to progeny.
Rea More: Effects of Friedreich's ataxia GAA repeats on DNA replication in mammalian cells