Variants in BTD (c.1270G > C; p. Asp424His); ASL (c.1300G > T; p.Val434Leu); GBE1 (c.985A > G; p.Tyr329Cys); and AGL (c.113C > G; p.T38S) have broadened the spectrum of mutations in these genes and provided additional evidence of involvement of these genes, when mutated, in various metabolic diseases. The gene discussed is ASL; the disease is metabolic disease.