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Trinucleotide expansion - The name of the syndrome was...

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Trinucleotide expansion The commonest inherited cause of mental retardation is a syndrome originally known as Martin-Bell syndrome. Patients are most usually male, have a characteristic elongated face and numerous other abnormalities including greatly enlarged testes. The pattern of inheritance of this disease was, at first, puzzling. It usually behaved as an X linked recessive condition but sometimes manifested itself in females and occasionally nonaffected transmitting males were found. In 1969 it was discovered that if cells from patients were cultured in medium deficient in folic acid their X chromosomes often displayed a secondary constriction near the end of the long arm.
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Unformatted text preview: The name of the syndrome was changed to the fragile X syndrome . The puzzling genetics remained unclear. Eventually the mutation was tracked down to a trinucleotide expansion in the gene now named FMR1 (Fragile site with Mental Retardation) at the site of the secondary constriction. As in the case of myotonic dystrophy symptomless premutations could occur (and were the cause of the transmitting males). Only when the premutation chromosomes were transmitted through females did expansion to the full mutant allele and phenotype occur. A number of diseases have now been ascribed to trinucleotide expansions. These include Huntington's disease ....
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