Prenatal Diagnosis of Bloom Syndrome Associated With Biallelic <scp>BLM RecQ</scp> ‐Like Helicase Variants Presenting With Severe Fetal Growth Restriction

Bloom syndrome (BS) is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, greatly increased risk of early-onset cancer, and the development of multiple malignancies. Few cases of BS diagnosed during the prenatal period have been reported. Here, I present the comprehensive clinical and genetic characterization of two unrelated fetuses diagnosed with BS. Two pregnant women with abnormal ultrasound findings underwent amniocentesis for karyotype analysis, copy number variation sequencing (CNV-seq), and trio-whole exome sequencing (Trio-WES). Both fetuses exhibited severe fetal growth restriction. One fetus had a pericardial effusion. The karyotype analysis and CNV-seq revealed no apparent abnormalities. Trio-WES revealed biallelically likely pathogenic or pathogenic BLM variants in the fetuses. All parents were BLM variant carriers. These cases indicate that affected fetuses are more likely to have severe fetal growth restriction and do not display significant chromosomal abnormalities before birth. Clarification of the molecular diagnosis had important implications for these parents because they carried a 25% risk of recurrence. They were recommended to plan future pregnancies with preimplantation genetic testing for monogenic disorders to avoid future offspring with BS.