Gaucher disease is an inborn error of metabolism caused by biallelic mutations in the glucocerebrosidase gene (GBA1), leading to deficiency of the enzyme glucocerebrosidase and the progressive accumulation of its substrate (glucocerebroside, Gb1) and its downstream metabolite (glucosylsphingosine, lyso-Gb1) in the lysosomes of mononuclear phagocytes. The gene discussed is GBA1; the disease is Gaucher disease.