45,X/46,XY MOSAICISM - CONTRAST OF PRENATAL AND POSTNATAL DIAGNOSIS

The process of prenatal diagnosis is unique in that the diagnosis and prognosis are made without seeing the patient. 45,X/46,XY mosaicism presents a special problem in this regard. The phenotype of 45,X/46,XY postnatally diagnosed children (pediatric group) was compared to that of 6 fetuses who were diagnosed from 7,000 amniocenteses (prenatal group). These amniocenteses were performed primarily because of an increased risk of chromosome abnormality. The pediatric group (age birth.sbd.18 yr) were all phenotypically abnormal, although none were mentally retarded. Seven patients presented with ambiguous genitalia, while 2 had primary amenorrhea. Sexual assignment was changed in 2. Abnormalities included rudimentary phallus, urogenital sinus, hypospadias, undescended testes, and short stature. All 9 patients required at least one surgical procedure. In contrast, the prenatally diagnosed fetuses (ages 3 months to 3 1/2 yr) were all phenotypically normal males. Four were noted to have male genitalia on ultrasonography. Thus, the phenotype of 45,X/46,XY mosaicism in prenatally diagnosed fetuses can be markedly different from that of individuals diagnosed postnatally. This must be considered when counseling patients.