A systematic review of monogenic etiologies of nonimmune hydrops fetalis.

Hydrops fetalis (HF), accumulation of fluid in two or more fetal compartments, is life-threatening to the fetus. Genetic etiologies include many chromosomal and monogenic disorders. Despite this, the clinical workup typically evaluates limited genetic targets. To support broader molecular testing of pregnancies with HF, we cataloged the spectrum of monogenic disorders associated with nonimmune hydrops fetalis (NIHF). We performed a systematic literature review under PROSPERO tag CRD42018099495 of cases reporting NIHF meeting strict phenotypic criteria and well-defined genetic diagnosis. We ranked the evidence per gene based on number of reported cases, phenotype, and molecular/biochemical diagnosis. We identified 131 genes with strong evidence for an association with NIHF and 46 genes with emerging evidence spanning the spectrum of multisystem syndromes, cardiac disorders, hematologic disorders, and metabolic disorders. Several genes previously implicated with NIHF did not have any reported cases in the literature with both fetal hydrops and molecular diagnosis. Many genes with strong evidence for association with NIHF would not be detected using current sequencing panels. Nonimmune HF has many possible monogenic etiologies, several with treatment implications, but current diagnostic approaches are not exhaustive. Studies are needed to assess if broad sequencing approaches like exome sequencing are useful in clinical management of HF.