ATP8B1 and liver disorder: Because a selective reduction of affinity may allow partial retention of the lipid flipping activity under physiological conditions, the observed differences between the mutants seem consistent with the clinical courses of the liver disease in the patients harbouring the ATP8B1 mutations: ATP8B1 L127P and E981K, equivalent to bATP8A2 I91P and E897K, give rise to PFIC1, which has a very severe clinical course, and ATP8B1 I344F, equivalent to bATP8A2 L308F, causes BRIC1, which has a milder clinical course.