PFIC type 1, also known as Byler's disease, is an autosomal recessive disease caused by homozygous or compound heterozygous mutations of the ATP8B1 (adenosine triphosphatase, type 8B, member 1, formerly named FIC1) gene on chromosome 18 locus q21-22, which encodes the FIC1 protein. This evidence concerns the gene ATP8B1 and progressive familial intrahepatic cholestasis type 1.