Prenatal diagnosis of low-level mosaicism for a small XIST-negative supernumerary ring X chromosome in a nondysmorphic male fetus.

摘要

A 27-year-old, primigravid woman underwent amnio-centesis at 19 weeks' gestation because of an abnormal maternal serum screening result. At 15 weeks' gestation, the woman had received a maternal serum multiple-marker screening test. The risk for Down syndrome was 1/138 calculated from the gestational age, maternal age, a maternal serum alpha-fetoprotein level of 0.870 multiples of the median (MoM), and a maternal serumfree beta -human chorionic gonadotrophin level of 3.911 MoM. In six separated colonies of amniocytes in two coverslips, a supernumerary ring marker chromosome was noted, while the other 17 colonies in two coverslips had a normal male kary-otype. The result was 46,XY[17]/47,XY,+mar. The parental karyotypes were normal. Repeated amniocen-tesis at 21 weeks' gestation revealed a karyotype of 46,XY[30]/47,XY,+mar in two coverslips.