Abstract
An Asian Indian female was found to have an elevated blood citrulline level by newborn screening. Plasma citrulline levels were mildly elevated between 110 and 366 [mu]mol/L with normal ammonia levels throughout the study period. Argininosuccinate synthetase deficiency was confirmed through molecular testing. Contrary to the mild biochemical presentation, fibroblasts argininosuccinate synthetase activity was undetectable. Education of the parents regarding the disorder and guidelines for a "sick day" diet and for medical treatment during illness to prevent and treat possible hyperammonemia were the main treatment strategies used. The patient was continued on a normal protein diet and had normal growth and development at 2 years of age.