Even though the export of OAS by the exporter YdeD is the main cause of intracellular OAS deficiency, the exporter had a positive flux control coefficient over most fluxes of the l-cysteine biosynthesis pathway, especially over SCYSSL, the last enzyme in the l-cysteine production path from thiosulfate. Here, SMOC1 is linked to hyperinsulinemic hypoglycemia, familial, 4.