RecruitingNatural History, Physiology, Microbiome and Biochemistry Studies of Propionic AcidemiaBackground: People s bodies need to break down food into the chemicals. These chemicals are used for energy and growth. Some people cannot process all chemicals very well. Too much of some chemicals can cause diseases. One of these diseases is called propionic acidemia (PA). People with PA can have problems with growth, learning heart, abdomen, and other organs. Researchers want to better understand how these problems happen. Objective: To learn more about propionic acidemia and the genes that might contribute to it. Eligibility: People at least 2 years old with PA who can travel to the clinic Some unaffected family members Design: Participants will have a 3 to 5-day hospital visit every year or every few years. Family members may have just 1 visit. During the family member visit, they may have: Medical history Physical exam Samples of blood and urine Questions about diet and a food diary Doctors and nurses may do additional studies: Samples of saliva, skin and stool Fluid from a gastronomy tube, if participants have one Dental and eye evaluations A kidney test - a small amount of dye will be injected and blood will be collected. Consultations with specialists A test of calories needed at rest. A clear plastic tent is placed over the participant to measure breathing. Stable isotope study. Participants will take a nonradioactive substance then blow into a bag. Photos taken of the face and body with underwear on Ultrasound of the abdomen Heart tests Hand x-ray Brain scan Participants may have other tests if study doctors recommend them. They will get the results of standard medical tests and genetic tests.