mental retardation group
Last reviewed 01/2018
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