Prenatal diagnosis of 45,X/46,XY mosaicism with postnatal confirmation in a phenotypically normal male infant

Abstract

Prenatal detection of chromosome mosaicism has always been a diagnostic dilemma. In 21 reported cases of chromosomal mosaicism in cultured amniotic fluid cells, only 2 cases had cytogenetic confirmation of the mosaicism. All 21 pregnancies resulted in either phenotypically normal liveborns or grossly normal abortuses. A case of XO/XY mosaicism detected prenatally and confirmed postnatally in a grossly normal male infant is reported. The indication for prenatal cytogenetic diagnosis was advanced maternal age (38 yr). A diagnosis of XO/XY mosaicism was made from 2 separate culture flasks of amniotic fluid cells, with 45,X cells predominating (86.4%). The Y chromosome was of normal size but carried no fluorescent band. The parents were counseled and were advised that the phenotype of XO/XY mosaicism can range from relative normality to sexual maldevelopment. They decided to continue this pregnancy. The infant was born at term and was a grossly normal male with normal penis and descended, normal-sized testes. Leukocyte culture from the cord blood and a skin fibroblast culture confirmed the mosaicism of XO/XY. The father''s Y chromosome was of identical size and carried a small fluorescent band. An altered Y chromosome may be predisposed to anaphase lag leading to mosaicism.