Trinucleotide repeat disorders

Trinucleotide repeat disorders are genetic conditions caused by an abnormal number of repeats (expansions) of a repetitive sequence of three nucleotides. These expansions are unstable and may enlarge which may lead to an earlier age of onset in successive generations - a phenomenon known as anticipation*. In most cases, an increase in the severity of symptoms is also noted

Examples - note dominance of neurological disorders

• Fragile X (CGG)
• Huntington's (CAG)
• myotonic dystrophy (CTG)
• Friedreich's ataxia* (GAA)
• spinocerebellar ataxia
• spinobulbar muscular atrophy
• dentatorubral pallidoluysian atrophy

*Friedreich's ataxia is unusual in not demonstrating anticipation