Mosaicism for structural non-centromeric autosomal rearrangement in prenatal diagnoses: evidence for sex-specific selection against chromosomal abnormalities.

Background: Mosaicism for chromosome rearrangements is common in preimplantation diagnoses, yet is rare in prenatal diagnoses as well as in other groups of patients referred to cytogenetic testing. Consequently, there is a lack of detailed studies on this kind of mosaicism in all groups of patients. Previous reports have identified a deficit of males among asymptomatic carriers of N/unbalanced Rea. Three mechanisms were proposed for explaining this phenomenon, including a high instability in the early female embryonic development, a male-specific selection against abnormal cells in the early embryo development, or a high intrauterine lethality of male carriers. To address these possibilities, we have performed a meta-analysis of male-to-female ratio (sex ratio, SR) in prenatally diagnosed and in spontaneously aborted carriers of mosaic Rea.

Results: One hundred and twenty one prenatally detected cases of normal cell line/autosome rearrangement mosaicism (N/Rea) with known carriers' sex were identified from the literature. Carriers of N/unbalanced Rea presented with 38 abnormal and 28 normal/apparently normal outcomes while carriers of N/balanced Rea presented with 24 normal and 3 abnormal outcomes. 58% of carriers of N/unbalanced Rea with an abnormal outcome displayed a high proportion (> 50%) of amniocytes with the abnormality compared to 25% of carriers with normal/apparently normal outcome. More female carriers of N/unbalanced Rea were identified with an abnormal outcome (15 M/23F) in contrast to a notable male predominance (18 M/10F) among those with normal outcome . Additionally, among spontaneously aborted carriers of N/unbalanced Rea, there was a strong female predominance (7 M/23F).

Conclusion: Previous reports have identified a deficit of male among asymptomatic carriers of N/unbalanced Rea. The current data suggests a male-specific selection against chromosomal abnormalities.