SLC37A4 and glycogen storage disease Ib: The G6PC gene variant causes the deficiency of glucose-6-phosphatase alpha (G6Pase-α) activity, which leads to GSD type Ia (OMIM#232200), accounting for about 80% of GSDI patients, whereas the SLC37A4 gene variant causes the deficiency of glucose-6-phosphate transporter protein (G6PT), which underlies GSD type Ib (OMIM# 232220), accounting for about 20% of GSDI cases [1, 2].