Fragile X

Fragile X is the leading cause of mental retardation. According to the SOGC in 2008 (Obstetrics Gynecological Society of Canada), when a premutated allele is transmitted from a mother to her offspring, there is usually an increase in the number of CGG repeats in the permutated allele. The number of repetitions in a premutation confers instability during transcription, to move towards full mutation causing mental retardation for future generations.

In the situations described below, the SOGC recommends screening for Fragile X:

  • Premature ovarian failure (25% of women have a premutation of the X chromosome);
  • Family who is experiencing fertility or reproductive problems associated with high follicle stimulating hormone (FSH) levels before the age of 40 or families where more than one woman is dealing with premature ovarian failure;
  • Individual with mental retardation;
  • Women with a personal history of autism, mental retardation, developmental delay of unknown etiology or whose family has at least one man with the same conditions (in a genealogical segment of three generations);
  • Individual with ataxia;
  • Families with a person with autism or mental retardation.

Given the seriousness of this disease, its high incidence in the general population, its effects on the family and on society as a whole, the SOGC recommends making the Fragile X screening desirable to women of childbearing age.

Other standards:

Canadian, American and international genetics Standards (CCMG: Canadian College of Medical Geneticists, ACMG: American College of Medical Genetics, ISCA consortium: International Standards for Cytogenomic Arrays) recommend as part of autism, mental retardation, delayed development and neurological conduct an analysis by DNA microarray. In addition, several recommendations promote the fragile X screening in conjunction with DNA microarray analysis.