Learning Objective: Understand the mechanism, inheritance patterns, and key features of major trinucleotide repeat expansion disorders, and recognize the concept of genetic anticipation.
Trinucleotide repeat expansion diseases are genetic disorders caused by the abnormal amplification of specific three-nucleotide (triplet) sequences in certain genes.
Genetic Anticipation:
In successive generations, disease severity increases and age of onset decreases due to further expansion of repeats.
Activity:
Major Trinucleotide Repeat Expansion Disorders
| Disease | Trinucleotide Repeat | Mode of Inheritance | Mnemonic / Key Features |
|---|---|---|---|
| Huntington disease | (CAG)n | Autosomal Dominant | “Caudate has ↓ ACh and GABA” |
| Myotonic dystrophy | (CTG)n | Autosomal Dominant | “Cataracts, Toupee (balding), Gonadal atrophy” |
| Fragile X syndrome | (CGG)n | X-linked Dominant | “Chin (protruding), Giant Gonads” |
| Friedreich ataxia | (GAA)n | Autosomal Recessive | “Ataxic GAAit” |
