PFIC groups havebeen defined according to the gene carrying the mutation: PFIC1 orByler’s disease, whose defective gene is ATP8B1 that encodes the amino-phospholipid flippase FIC1; PFIC2 which resultsfrom the expression of BSEP variants encoded by mutated versions of ABCB11 gene and PFIC3, that results from mutations in the ABCB4 gene encoding the MDR3 protein (multidrug resistanceprotein 3; MDR2 in mice).2 The gene discussed is ATP8B1; the disease is glycogen storage disease VI.