Chimerism in Males and Recurrent Miscarriages: A Case Study

Chimerism is a rare biological phenomenon in which an individual harbors two or more genetically distinct cell lines, typically resulting from the fusion of two embryos or from twin-to-twin cell transfer in utero. Though often asymptomatic, chimerism can have significant implications for fertility, development, and immunological compatibility. Its true prevalence remains unknown due to frequent underdiagnosis, especially in the absence of phenotypic clues. Recurrent pregnancy loss, defined as the occurrence of two or more consecutive miscarriages, is often attributed to chromosomal abnormalities, uterine malformations, thrombophilia, or immune dysfunction. Paternal contributions, particularly involving rare genetic anomalies, are far less investigated. Here, we report a unique case of a male with 46,XX/46,XY chimerism, discovered during the evaluation of a couple with three consecutive pregnancy losses. We hypothesize that the presence of 46,XX germ cells in the testes might give rise to epigenetically abnormal spermatozoa, which could disrupt embryonic development through faulty genomic imprinting. Although causality cannot be confirmed in the absence of functional assays, we propose that chimerism might represent an underrecognized and understudied cause of recurrent miscarriage. This case highlights the need to further explore rare paternal genetic configurations in the context of unexplained recurrent pregnancy loss.