Regions of "trinucleotide repeats" are seen in -

Ans. is 'b' i.e., Huntington's disease Huntingtons disease is caused bv triplet repeat expansion nucleotideo Huntington disease (HD) is caused by expansion of the cytosine-adenin e-suanine (CA G) trinucleotide repeats in the HTT sene (also known as the HD or IT15 gene) located on chromosome 4pl6.3 that encodes the protein huntingtin.o Mutant huntingtin contains an expanded tract of glutamine residues, which is located near its amino terminal.o The disease is transmitted in an autosomal dominantQ manner.o Unstable trinucleotide repeats are associated with a variety of neurodegenerative diseases.Nine of these disorders are associated with expansion ofcytosine-adenine-guanine (CAG) repeats that encode for polyglutamine tracts in the protein products.Included in this group are Huntington disease (HD), spinobulbar muscular atrophy, dentatorubral pallidoluysian atrophy, and some of the spinocerebellar ataxias.o The most common presenting symptom of HD in adults is chorea (hence the name Huntington chorea).Other usual findings at presentation include memory deficits, affective disturbances, personality changes, and other manifestations of motor dysfunction such as parkinsonism and dystonia.