Biliary atresia is the most severe form of cholestatic liver disease. The children have high morbidity and mortality and get devastating pruritus and fatigue, failure to thrive, progressive hepatic failure and impaired neurodevelopment. The etiology is mostly unknown. More than half need a new liver from a living or deceased donor during childhood. However, correct timing of the transplantation is extremely difficult because of lack of consensus based on clinical assessment tools. All though the incidence is low, the cost of this disease is tremendous from both a clinical and human perspective. So far, protocolized neurodevelopment tests, genetic profiling, precise malnutrition evaluation based on clinical appearance, biochemical markers and brain MRI-scans, body composition, immunological function, level of physical activity and optimal time of transplantation in cholestatic children are unknown. The aim is to determine risk factors for neurocognitive impairment in children suffering from severe cholestasis in order to determine optimal time for liver transplantation from a brain perspective. In a prospective study, the investigators will investigate risk factors related to brain-, heart-, gut- and immunological function in the Danish cohort. This cohort consists of 75 children aged 0-18 years. In addition, 30 aged and gender matched healthy and 20 tetra fallot children will serve as control groups. The children will undergo extensive and advanced liver function evaluation, genetic profiling, nutrition and immunological status, neuro-imaging and neurocognitive evaluation at time of diagnose, 2 years of age, pre-school, pre-teenage, and teenage. In case of a liver transplantation, additional neuro-cognitive tests will be performed