Trinucleotide repeat is seen in

(A) Fragile X syndrome # Trinucleotide repeat disorder> Trinucleotide repeat disorders (also known as trinucleotide repeat expansion disorders, triplet repeat expansion disorders or codon reiteration disorders) are a set of genetic disorders caused by trinucleotide repeats in certain genes exceeding the normal, stable, threshold, which differs per gene.> The mutation is a subset of unstable micro satellite repeats that occur throughout all genomic sequences.> If the repeat is present in a healthy gene, a dynamic mutation may increase the repeat count and result in a defective gene.> The first triplet disease to be identified was fragile X syndrome that has since been mapped to the long arm of the X chromosome.> At this point, there are from 230 to 4000 CGG repeats in the gene that causes fragile X syndrome in these patients, as compared with 60 to 230 repeats in carriers and 5 to 54 repeats in normal persons.> The chromosomal instability resulting from this trinucleotide expansion presents clinically as mental retardation, distinctive facial features, and macroorchidism in males.> The second, related DNA-triplet repeat disease, fragile X-E syndrome, was also identified on the X chromosome, but was found to be the result of an expanded GCC repeat.> Identifying trinucleotide repeats as the basis of disease has brought clarity to our understanding of a complex set of inherited neurological diseases.