Trinucleotide expansions cause at least 30 diseases. Many are inherited predominantly through paternal transmissions, which are probably the result of germ-cell-specific mutations. A recent study of testicular germ cells in HD patients revealed that expansions occur in diploid cells before the completion of meiosis. Therefore, expansions are not limited to the late-haploid spermatids, in which the genome is 'sleeping'.

Classification

 polyglutamine repeat disorders (CAG repeats)

• myotonic dystrophy
• Huntington's disease
• Kennedy's disease
• fragile X syndrome
• spinocerebellar ataxias
• Friedreich's ataxia

 polyalanine repeat disorders

References

 Brown LY, Brown SA. Alanine tracts: the expanding story of human illness and trinucleotide repeats. Trends Genet. 2004 Jan;20(1):51-8. PMID: #14698619#

 Pearson CE. Slipping while sleeping? Trinucleotide repeat expansions in germ cells. Trends Mol Med. 2003 Nov;9(11):490-5. PMID: #14604827#

 Nag DK. Trinucleotide repeat expansions: timing is everything. Trends Mol Med. 2003 Nov;9(11):455-7. PMID: #14604819#

 Cummings CJ, Zoghbi HY. Fourteen and counting: unraveling trinucleotide repeat diseases. Hum Mol Genet. 2000 Apr 12;9(6):909-16. PMID: #10767314#