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Mental retardation group

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To date, there are three distinct mutations on the X-chromosome which produce mental retardation. They are combined into the congenital fragile X syndrome.

The genetic lesions are characterized by:

  • expansion of CGG/CCG repeats
  • very large numbers of repeats, typically 200-2000 in affected individuals
  • there is marked genetic anticipation; larger numbers of repeats result in early onset and severe disease
  • the CGG/CCG repeats are transcribed into non-coding regions of mRNA's

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