Sequencing of genes encoding for hepatic transporters for bile acid homeostasis (BSEP, MDR3, and FIC1) found no genetic variants typically associated with hereditary cholestasis syndromes.
Three exemplary clinical cases of infants with cholestasis are presented and discussed in the context of their genetic and histopathological findings (autosomal recessive polycystic kidney disease, atypical PFIC and Niemann-Pick syndrome type C1).
Children with normal γ-glutamyltransferase cholestasis (n = 47; 13 patients with ATP8B1 deficiency, 19 with ATP-binding cassette, subfamily B (MDR/TAP), member 11 (ABCB11) deficiency, and 15 without either ATP8B1 or ABCB11 mutations) were enrolled.
Progressive familial intrahepatic cholestasis type 1 (PFIC1), an inherited liver disease caused by mutations in ATP8B1, progresses to severe cholestasis with a sustained intractable itch.
Although the exact etiology of cholestasis is incompletely understood, it is hypothesized that ATP8B1 deficiency results in enhanced cholesterol extraction from the canalicular membrane, which impairs the function of the bile salt export pump (BSEP), resulting in cholestasis.
Our findings point to a critical role of ATP8B1 in apical membrane organization that is unrelated to its presumed aminophospholipid translocase activity, yet potentially relevant for the development of cholestasis and the manifestation of extrahepatic features associated with ATP8B1 deficiency.
Homozygous mutations in the ATP8B1 gene cause cholestasis with a normal serum gamma-glutamyl transpeptidase (gamma-GT), and have been reported in two forms of cholestasis: progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign recurrent intrahepatic cholestasis (BRIC).
Cholestasis Familiaris Groenlandica (CFG, or progressive familiar intrahepatic cholestasis type 1 (PFIC1)) is a very common lethal recessive inherited disease in Greenland.
The localization of FIC1 in the canalicular membrane and cholangiocytes suggests that it may directly or indirectly play a role in bile formation since mutations in FICI are associated with severe symptoms of cholestasis.
The biochemical and cellular functions of its product, FIC1, and the mechanisms by which its absence or dysfunction leads to cholestasis are currently elusive.
These data establish Greenland familial cholestasis as a form of progressive familial intrahepatic cholestasis type 1 and further underscore the importance of unimpeded FIC1 activity for normal bile formation.
Its protein product is likely to play an essential role in enterohepatic circulation of bile acids; further characterization of FIC1 will facilitate understanding of normal bile formation and cholestasis.