Propionic-2,2-d2 acid is a deuterated compound of Propionic acid. Propionic acid has a CAS number of 79-09-4. Propionic acid (PA) is widely used as an antifungal agent in food. It is present naturally at low levels in dairy products and occurs ubiquitously, together with other short-chain fatty acids (SCFA), in the gastro-intestinal tract of humans and other mammals as an end-product of the microbial digestion of carbohydrates. It has significant physiological activity in animals. PA is irritant but produces no acute systemic effects and has no demonstrable genotoxic potential.Propionic aciduria is one of the most frequent organic acidurias, a disease that comprise many various disorders. The outcome of patients born with Propionic aciduria (genetic disorder) is poor intellectual development patterns, with 60% having an IQ less than 75 and requiring special education. Successful liver and/or renal transplantations, in a few patients, have resulted in better quality of life but have not necessarily prevented neurological and various visceral complications. These results emphasize the need for permanent metabolic follow-up whatever the therapeutic strategy. Decreased early mortality, less severe symptoms at diagnosis, and more favorable short-term neurodevelopmental outcome were recorded in patients identified through expanded newborn screening.