The NIH UNI Study: Urea Cycle Disorders, Nutrition and Immunity

Objectives: * To study nutrition and immune system problems in people with urea cycle disorders. * To study how people with urea cycle disorders and healthy volunteers respond to standard flu and/or hepatitis A vaccines. * To compare differences in nutrition and immune systems of people with urea cycle disorders with that of healthy volunteers. Eligibility: * Healthy males and females at least 2 years of age who are able to travel to the National Institutes of Health hospital in Bethesda, MD * Males and females at least 2 years of age who have a urea cycle disorder and are able to travel to the National Institutes of Health hospital in Bethesda, MD. Design: For Patients with urea cycle disorder: * Participants will spend 2 to 3 days in the National Institutes of Health hospital for the following tests: * A physical exam and review of medical history * Food log for 3 days before the start of the study * Blood tests * 24-hour urine collection * Resting metabolism test * DEXA scan imaging study of bones and body fat * Participants who are old enough to do certain tasks by themselves (like dressing and eating) can choose to have the following extra tests: * 24-hour metabolic room measurements * BodPod(Registered Trademark) study to measure bones and body fat * Participants may choose to have a flu shot and/ or Hepatitis A shot at the end of the study and will be monitored to check for possible side effects. * Participants will return within 1 to 3 months for follow-up tests/immunizations. For Healthy Volunteers: * Participants will be seen at the outpatient clinics at the National Institutes of Health hospital for up to 2 visits for the following: * Review food log completed 3 days before the start of the study * Blood tests * Participants may choose to have a flu shot and/ or Hepatitis A shot at the end of the study and will be monitored to check for possible side effects. * Participants will return within 1 to 3 months for follow-up tests/immunizations. * Revi