WSB2 and fetal growth restriction: Here, we describe five patients from four unrelated families affected by developmental delays, brain anomalies, and dysmorphic features with or without intrauterine growth restriction (IUGR) and hypotonia, who were found to have homozygous, ultra-rare, predicted loss-of-function (pLoF) or missense variants in WSB2. We report the findings from a comprehensive phenotypic screening of the Wsb2-mutant (mut) mice which suggests overlapping findings between human disease and mouse model.