General Medical Information

Monosomy X (Turner’s Syndrome)

Joe Leigh Simpson

The complement most frequently associated with ovarian dysgenesis is 45,X. The proportion of 45,X individuals in a given sample will depend on the method of ascertainment. Fewer 45,X individuals will be detected if primary amenorrhea is the presenting complaint than if short stature or various somatic anomalies are the presenting complaints. Primary amenorrhea is more likely to be the presenting complaint in women ascertained by gynecologists, whereas short stature is likely in children ascertained by pediatricians. Overall, about 50% of all patients with gonadal dysgenesis have a 45,X complement; 25% have sex chromosomal mosaicism with a structural abnormality (e.g., 45,X/46,XX). Far fewer have a structurally abnormal X or Y chromosome.

In 80% of cases, the paternally derived X has been lost. The phenotype does not in general differ between 45,Xm and 45,Xp cases (Xm,X of maternal origin; Xp,X of paternal origin). In structurally abnormal X chromosomes, it is also the paternal X that is lost. This suggests that Xm and Xp chromosomes are lost at random. Assuming 45,Y is lethal, the theoretical percentage of 45,Xm cases would be 67%, which is not greatly different from the 80% actually observed.