Recently, four studies reported a small series of patients with PFIC who were negative for mutations in the known PFIC genes and harbored biallelic MYO5B mutations, or pathogenic monoallelic MYO5B mutations, where a mutation on the second allele had not been detected with the current diagnostic techniques [9,10,11,26]. This evidence concerns the gene MYO5B and progressive familial intrahepatic cholestasis.