Glycerol kinase deficiency (GKD) is an X‐linked recessive disorder due to glycerol kinase (GK) gene mutations resulting in hyperglycerolermia, hyperglyceroluria, and “pseudohypertriglyceridemia.” In vivo glycerol metabolism has not been assessed in GKD. The gene discussed is GK; the disease is isolated glycerol kinase deficiency.