<prompt> Which is not true about Fragile X syndrome?Large testisPigmented neviLarge ear presentNo large nose  <response>: Fragile - X syndrome Fragile - X syndrome is the prototype of diseases in which the mutation is characterized by a long repeating sequence of three nucleotides.In fragile X syndrome, trinucleotide repeat mutation involves CGG on the non-coding region.Clinical features of fragile - X syndromeMental retardation Long face with large mandibleHyperextensible joint Mitral valve prolapseLarge everted earsLarge testis macroorchidism High arched palate Fragile X syndrome is the second most common cause of mental retardation, after Downs syndrome. 