Homozygous and heterozygous compound mutations of the SLC37A4 gene on chromosome 11q23.3 cause an AR disorder that compromises both glycogen metabolism and glycosylation and thus can be defined both as glycogen storage disease type Ib (GSDIb) and as congenital disorder of glycosylation type IIw (CDG2W) [OMIM:619525]. The gene discussed is SLC37A4; the disease is glycogen storage disease Ib.