Lysinuric protein intolerance presenting deficiency of argininosuccinate synthetase

A 35-yr-old woman, who suffered from relapsing coma with hyperammonemia for 17 yr, was diagnosed to have lysinuric protein intolerance (LPI). Increased urinary dibasic amino acids (lysine, arginine and ornithine) and impaired absorption of orally administered lysine and arginine proved the defects of renal tubular and intestinal transport of dibasic amino acids. These defects are the primary cause of impaired urea cycle metabolism in LPI. Further, the level of argininosuccinate synthetase (ASS), a urea cycle enzyme, was analyzed and it was found to be below the normal level. This is the second reported case of LPI presenting ASS deficiency.