This is a prospective mixed-design study focused on the long-term management of propionic aciduria (PA) and methylmalonic aciduria (MMA) with N-carbamylglutamate (NCG) maintenance therapy. Treatment characteristics, clinical outcomes, and healthcare utilization data of patients diagnosed PA or MMA treated \>6 months therapy with NCG are collected at baseline, 12 months, 18 months, 36 months and 54 months. Qualitative interviews with adult patients and caregivers are conducted \>6 months after study enrollment to gain a better understanding of the disease burden and the treatment burden of patients and their families.