<prompt> Genetic abnormality in fragile x syndrome-Trinucleotide repeatsPoint mutationNot inheritableDeletion  <response>: Fragile X syndrome is the prototype of diseases in which the mutation is characterized by a long repeating sequence of 3 nucleotides.These mutations are characterized by amplification of a sequence of three nucleotides.Although the specific nucleotide sequence that undergoes amplification differs in various disorders, almost all affected sequences share the nucleotides Guanine G and cytosine C.Also, know -It is the second most common cause of mental retardation after Downs syndrome.It is an X linked disorder characterized by an inducible cytogenetic abnormality in the X chromosome and an unusual mutation within the familial mental retardation -1 FMR-1 gene.Trinucleotide Repeat disordersExpansions affecting the non-coding regionFragile X syndromeFrederichs ataxiaMyotonic dystrophyExpansions affecting coding regionSpinobulbar muscular atrophyHuntingtons diseaseDentatorubral pallidoluysianSpinocerebellar ataxia type 1Spinocerebellar ataxia type 2Spinocerebellar ataxia type 3Spinocerebellar ataxia type 6Spinocerebellar ataxia type 7 