Participation in this study will last 10 years and will consist of a baseline visit and five annual follow-up visits. The study will enroll infants through adults 25 years of age who have, or are suspected of having, one of the four genetic cholestatic liver diseases. Individuals who are siblings of a-A1T participants and have underlying disease with no evidence of liver involvement may also be enrolled. Study visits will involve review of clinical information, family history, and any clinically indicated treatments and their outcomes; a physical exam; laboratory tests; and radiologic and imaging evaluations. In addition to these standard of care evaluations, participants will undergo several special research evaluations, including quality of life questionnaires, neurodevelopmental evaluations, hearing exams, DEXA scanning (dual energy x-ray absorptiometry), liver histology studies, and collection of serum, plasma, urine, and blood for DNA or cell lines. Serum, plasma, urine, and blood for DNA or cell lines will also be collected from both biological parents and from affected siblings of participants with a-A1T or ALGS. Genetic testing will be performed using the collected specimens.