Perinatal-Lethal Non-Immune Fetal Hydrops Attributed to MECOM-associated Bone Marrow Failure

Pathogenic variants inMECOM, a gene critical to the self-renewal and proliferation of hematopoietic stem cells, are known to cause a rare bone marrow failure syndrome associated with amegakaryocytic thrombocytopenia and bilateral radioulnar synostosis known as RUSAT2. However, the spectrum of disease seen with causal variants inMECOMis broad, ranging from mildly affected adults to fetal loss. We report two cases of infants born preterm who presented at birth with symptoms of bone marrow failure including severe anemia, hydrops, and petechial hemorrhages; radioulnar synostosis was not observed in either patient, and, unfortunately, neither infant survived. In both cases, genomic sequencing revealed de novo variants inMECOMconsidered to be responsible for their severe presentations. These cases add to the growing body of literature that describeMECOM-associated disease, particularlyMECOMas a cause of fetal hydrops due to bone marrow failure in utero. Furthermore, they support the use of a broad sequencing approach for perinatal diagnosis, asMECOMis absent from available targeted gene panels for hydrops, and highlight the importance of postmortem genomic investigation.