N-Acetylglutamate Synthase Deficiency (NAGS)
N-acetylglutamate synthase deficiency is an autosomal recessive, pan-ethnic disorder caused by pathogenic variants in the gene NAGS. Onset is typically in the first days of life. Affected infants quickly develop an excess of ammonia in the blood, which causes vomiting, lethargy, and coma, and is fatal if not quickly treated. The longer that the patient experiences an excess of ammonia in the blood, the more severe the resulting brain damage will be. A milder form with a later onset may occur. While some pathogenic variants have been associated with early or late onset, the paucity of reported patients makes it difficult to predict the severity of the disease based on the genotype. Without treatment, hyperammonemia episodes are fatal; however, early diagnosis and proper treatment can improve the prognosis greatly.
For information about carrier frequency and residual risk, please see the residual risk table.