Using SNP microarray to distinguish mosaicism from chimerism in a phenotypically normal male newborn with prenatal...

The coexistence of 46,XX/46,XY cells in cultured amniotic fluid sample is not uncommon. The vast majority of these cases are the result of contamination by maternal cells in an otherwise normal male fetus. However, this finding might be true chimera or mosaicism, which can be associated with sexual ambiguity. Conventional cytogenetic study could not exclude these abnormalities. Here, we present a case of 46,XX/46,XY at amniocentesis and ascertained a mosaicism by postnatal single nucleotide polymorphism (SNP) array in a phenotypic male newborn.

A fetus of a 37-year-old nulliparous woman underwent amniocentesis at 19 weeks of gestation because of advanced maternal age. Chromosome analysis of the first and second samples revealed a mixture of 46,XX and 46,XY cell lines. Prenatal ultrasound examination showed normal male genitalia. After birth, peripheral blood samples were analyzed by karyotyping, fluorescence in situ hybridization (FISH), SNP array, and short tandem repeat (STR) analysis. These studies confirmed 46,XX/46,XY mosaicism in a phenotypically normal male newborn.

Our case is the second report of 46,XX/46,XY mosaicism noted by prenatal cytogenetic study and confirmed by postnatal SNP array with normal male genitalia. When encountering XX/XY in prenatal diagnosis, SNP array is a useful tool to distinguish maternal cell contamination from chimera or mosaicism. Detailed prenatal ultrasound for the genitalia is required for the prediction of prognosis. The fetus may have a favorable outcome without ultrasound abnormalities.