Decreased concentration of free histidine in serum in rheumatoid arthritis, an isolated amino acid abnormality not associated with generalized hypoaminoacidemia.

The serum concentrations of 12 free amino acids (alanine, arginine, glycine, histidine, isoleucine, leucine, lysine, phenylalanine, serine, threonine, tyrosine, and valine) were measured in 26 patients with rheumatoid arthritis and in 12 control subjects. Patients with rheumatoid arthritis had a low serum histidine concentration (P equals 0.002) but no abnormality of any other amino acid concentration or of the combined concentration of the measured amino acids, excluding histidine. These data and 22 other reported studies provide strong evidence for the presence of hypohistidemia, not associated with generalized hypoaminoacidemia, in patients with rheumatoid arthritis. (J Rheumatol 2: 384-392, 1975).