Hyperdibasicaminoaciduria and hyperammonemia in familial protein intolerance.

A 3-year-old boy with hyperdibasicaminoaciduria and hyperammonemia showed characteristics of familial protein intolerance (FPI). Oral loading tests of lysine and arginine disclosed a remarkably reduced capability for intestinal absorption of these amino acids. Because urinary excretion and renal clearance of dibasic amino acids were only moderately elevated in the patient, the conspicuously decreased serum concentration of lysine, arginine, and ornithine was attributed to the defect in internal absorption. A possible explanation for elevated blood ammonia levels in FPI is that it is due to a deficiency of arginine and ornithine in the urea cycle that in turn results from a severe impairment in absorption of the amino acids by the gut mucosa.