As expected, both the membrane and secreted isoforms carrying the p.Ser22Pro variant (the only coding variant found in the homozygous state in public databases) were produced in normal amounts and functional (Figure 2B-E), suggesting that autosomal recessive FLT3L deficiency is exceedingly rare globally. Here, FLT3LG is linked to hyperinsulinemic hypoglycemia, familial, 4.