Patients with LAD who weigh at least 12 kg (26.4 LB), who do not have an active infection, and who have a family member that is a well-matched donor may be eligible for this study. Pregnant or breast feeding women may not participate. Candidates will have a medical history, physical examination and blood tests, lung and heart function tests, X-rays or computed tomography (CT) scans of the body, and dental and eye examinations. They will fill out questionnaires that measure emotional well being, quality of life and intelligence (the ability to learn and understand).