meiotic instability could result in a dynamic mutation that increases the number of repeats in offspring inheriting the mutant allele. Once the number of copies reaches over 100, the disease will manifest earlier in life (although the individual will still reach adulthood before the symptoms are evident) and the symptoms will be more severe – including electrical myotonia. As the number progresses upwards past 400, the symptoms show themselves during childhood or infancy. Examples of diseases showing anticipation Diseases showing anticipation include: Autosomal dominant Several spinocerebellar ataxias Huntington's disease – CAG Myotonic dystrophy – CTG Dyskeratosis congenita – TTAGGG (telomere repeat sequence) Autosomal recessive Friedreich ataxia – GAA (Note: Friedreich ataxia does not usually exhibit anticipation because it is an autosomal recessive disorder.) X-linked Fragile X syndrome – CGG Without expression type Crohn's disease Behçet's disease References External links Genetic disorders by mechanism