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Many metabolic disorders manifest themselves in the weeks and months after birth, when the infant fails to properly utilize its new food sources. This is the case with propionic acidemia, in which the newborn develops a severe acidosis, dehydration, lethargy, and coma. A case has now been seen, however, in which propionic acidemia appeared in a patient with chorea and dementia which began in adulthood. A 31-year-old man was evaluated for deterioration in his psychiatric condition, which had begun three years earlier. Beginning at age 28, he had gradually become withdrawn and confused, while his memory deteriorated. The patient exhibited the involuntary but coordinated movements of chorea, and engaged in bizarre behavior at times. Laboratory investigation revealed elevated quantities of propionic acid and its metabolites. Some other substances were also found to be elevated, including 2-butanone, 2-pentanone, and 4-heptanone. A culture of skin fibroblasts from the patient revealed a deficiency in activity of the enzyme propionyl CoA carboxylase; this deficiency was the cause of his propionic acidemia. The amino acids isoleucine, valine, and methionine are all precursors of propionic acid, and thus propionic acidemia is often an indication of protein intolerance. The patient was placed on a low-protein diet, but unfortunately no improvement was observed. Propionic acidemia may be the net result of a variety of different inborn errors of metabolism. In the case of this patient, the mother recalled rare episodes of nausea, vomiting, and lethargy when the patient was an infant, but no diagnosis was made at that time. The child recovered from these episodes when he was fed clear liquids. The patient's history and present laboratory values suggest that he may actually have suffered from a marginal defect of propionic acid metabolism all his life, which only resulted in obvious deficits during young adulthood. The case indicates that a metabolic workup is always appropriate for patients with neurological symptoms without an obvious cause, even if the patient is an adult. (Consumer Summary produced by Reliance Medical Information, Inc.)