Fragile X syndrome: relation to premature ovarian failure and infertility treatment.

摘要

Fragile X syndrome is the most common form of inherited mental retardation and has wide genetic and social implications for the effected family. Down's syndrome is the most common chromosomal cause for mental retardation but it is generally sporadic. The gene that is inactivated in fragile X syndrome (FMR1 -fragile X mental retardation gene-1) is located on the long arm of the X chromosome and was identified in 1991. The FMRl-gene has a DNA sequence consisting of repeated CGG trinucleotides. In the general population the number of CGG repeats in the FMRl-gene varies between 6 and 50. In fragile X premutation carriers the number of CGG repeats has expanded to 50-200 and in fragile X full mutation the number of CGG repeats has expanded to >200 due to genetic amplification. There is a borderline zone between 45 and 55 CGG repeats when the allele may be stable or unstable. With 50-200 CGG repeats there is an increased level of FMR1 mRNA. When there is an expansion >200 CGG repeats the FMR1 gene is methylated and transcription and production of FMR1 protein is silenced. The FMR1 protein is proposed to play a role in synaptic and oocyte function.