Diseases caused by mutations that causes repeat expansion in non-coding regions

Mutations that causes repeat expansion in non-coding regions contribute to neurogenerative diseases such as fragile X syndrome (OMIM #300624) and myotonic dystrophy (OMIM #160900).

.0004 FRAGILE X MENTAL RETARDATION SYNDROME
FRAGILE X TREMOR/ATAXIA SYNDROME, INCLUDED
PREMATURE OVARIAN FAILURE 1, INCLUDED

FMR1, (CGG)n EXPANSION

Kremer et al. (1991) demonstrated that the presence of an unstable expanded trinucleotide repeat sequence, designated p(CCG)n, in the 5-prime untranslated region of the FMR1 gene is the basis of fragile X syndrome (300624). The authors showed that normal X chromosomes have about 40 +/- 25 copies of p(CCG)n and that within these limits the sequence is a stable DNA polymorphism. The fragile X genotype was characterized by an increased amount of unstable DNA that maps to the repeat. The mutation causing fragile X syndrome contains over 200 CCG repeats (Devys et al., 1992).


myotonic dystrophy (OMIM #160900)

A number sign (#) is used with this entry because myotonic dystrophy-1 (DM1) is caused by a heterozygous trinucleotide repeat expansion (CTG)n in the 3-prime untranslated region of the dystrophia myotonica protein kinase gene (DMPK; 605377) on chromosome 19q13.

A repeat length exceeding 50 CTG repeats is pathogenic (Musova et al., 2009).

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