Diagnosis of Martin–Bell syndrome. Fragile X syndrome: determination of the number of CGG repeats
Fragile X syndrome (Martin–Bell syndrome) is a genetic disorder that causes intellectual disability, behavioral and learning difficulties, and affects the patient's physical characteristics.
Although fragile X syndrome can occur in individuals of either sex, males are affected more frequently than females, and the condition is generally more severe in males.
Under normal circumstances, the number of CGG repeats on the X chromosome ranges from 6 to 50. Martin–Bell syndrome develops in individuals with more than 200 CGG repeats.
Women are more likely to have a premutation, defined as 55-200 CGG repeats. In this case, intellectual disability and the clinical manifestations of the syndrome do not develop. However, women carrying an FMR1 premutation may experience premature ovarian insufficiency, as well as infertility or recurrent pregnancy loss.