MNEMONIC: Diseases showing anticipation associated with Triplet Repeat Expansion
Anticipation: pattern of inheritance, symptoms of a genetic disorder become apparent at an earlier age as it is passed on to the next generation, an increase of severity of symptoms is also noted
Huntington Disease (HD)
- Mnemonic: “HD es una CAGada” in Spanish, cagada means something bad, shitty, to be more precise. This is to remember the CAG trinucleotid repeat.
- Autosomal Dominant, chromosome 4: “Huntin’ 4 food”
- Chorea: purposeless movement of limbs, due to a loss of GABAergic neurons of neostriatum (caudate nucleus and putamen) of indirect pathway.
- Personality changes, dementia, tendency for suicide
Fragile X Syndrome
- CGG trinucleotid repeat
- X dominant, FMR 1
- Mental retardation, large ears and jaw. post-pubertal macro-orchidism (males), attention deficit disorder (females)
- GAA trinucleotid repeat
- Autosomal recessive, Frataxin gene, chromosome 9
- Neuronal degeneration: dorsal root ganglia, Clarke column (spinocerebellar tract), posterior column of spinal cord, dentate nucleus, Purkinje cells, Betz neurons, CN nuclei of VII, X, XII
- Progressive gait & limb ataxia, arreflexia, hypertrophic cardiomyopathy, axonal sensory neuropathy, kyphoscoliosis, dysarthria, hand clumsiness, loss of sense of position, impaired vibratory sensation.
- CTG trinucleotid repeat
- Autosomal Dominant, MD1: chromosome 3; MD2: chromosome 19
- Muscle loss, cardiac arrythmia, testicular atrophy, frontal baldness, cataracts.