new mutation causing progressive familiar intrahepatic cholestasis type 3 in association with autoimmune hepatitis. ABSTRACT Background: Some patients exhibit features of both autoimmune hepatitis (AIH) and primary sclerosing cholangitis (PSC). Similarly, patients with progressive familial intrahepatic cholestasis type 3 (PFIC3) may share histological features with PSC. Case report: We report the case of a 22-year-old man who, since he was 5 years of age, has presented with pruritus, an

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... ately ninefold elevation of aminotransferases, and γ-glutamyl transferase levels ~10 times the upper limit. Initially he was diagnosed with an overlap syndrome of small duct PSC plus AIH. However, fluctuations in liver enzymes were observed over the following years. Analysis of the ABCB4 gene indicated the diagnosis of PFIC3, revealing a mutation not previously reported. Conclusion: With this case report we aim to describe a new mutation, raise awareness of this rare pathology and highlight the importance of genetic testing of the ABCB4 gene in patients with autoimmune liver disease (mainly small duct PSC) with incomplete response to immunosuppressive treatment. LEARNING POINTS • Autoimmune liver diseases have a wide spectrum of manifestations. • Cholangiopathies such as ABCB4 deficiency have histological features quite similar to those seen in small duct primary sclerosing cholangitis. • The new mutation of the ABCB4 gene described in this article is compatible with the diagnosis of progressive familial intrahepatic cholestasis type 3, which is probably less rare than usually thought.