OBJECTIVETo investigate the plasma amino acid spectrum in infants more than 1-year-old with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) in order to identify potential diagnostic markers of NICCD.

METHODSInfants less than 1 year of age who had been referred to our hospital for investigation of suspected conjugated hyperbilirubinemia between June 2003 and June 2009 were eligible for enrollment. A total of 182 infants were enrolled and divided into three groups: infants diagnosed with NICCD (n = 24), according to gene testing and/or western blotting results; infants diagnosed with biliary atresia (BA; n = 20), according to intra-operative cholangiography findings; and infants diagnosed with idiopathic neonatal intrahepatic hepatitis (INH; n = 138), according to exclusionary findings for diseases affecting the extrahepatic biliary system and no positive serology results to indicate infections with hepatitis B, C, A or E, toxoplasmosis, rubella, herpes simplex, human immunodeficiency virus-1, or syphilis. The plasma amino acid spectrum of each infant was analyzed by tandem mass spectrometry (MS/MS). The concentrations of 18 amino acids, as well as the ratio of each amino acid to total amino acids, were compared among the three groups. Selected ratios of amino acids were analyzed by receiver operating characteristic (ROC) curve analysis.

RESULTSCompared with the BA and INH groups, the NICCD group had significantly lower levels of alanine (Ala; 175.7 and 205.7 vs. 136.3 mumol/L, P = 0.0001), aspartic acid (Asp; 47.5 and 43.1 vs. 31.55 mumol/L, P = 0.0041), glutamic acid (Glu; 276.16 and 263.24 vs. 175.71 mumol/L, P = 0.0075) and tryptophan (Trp; 41.90 and 47.97 vs. 28.51 mumol/L, P = 0.0003), but significantly higher levels of methionine (Met; 28.24 and 29.35 vs. 71.40 mumol/L, P = 0.0390), tyrosine (Tyr; 55.8 and 57.02 vs. 116.81 mumol/L, P = 0.0072) and citrulline (Cit; 15.09 and 15.65 vs. 97.42 mumol/L, P = 0.0001). The ratio of each amino acid to total amino acids showed the same trends for the NICCD group. The calculated areas under the ROC curves of the ratios of Cit, Tyr, and Met to the total amino acids were 0.874 (95% CI: 0.752 - 0.996), 0.814 (95% CI: 0.706 - 0.923), and 0.705 (95% CI: 0.535 - 0.875) respectively. The calculated area under the ROC curve of the ratio of Cit to Ala was 0.893 (95% CI: 0.781 - 1.005), and when the cut-off value of the ratio of Cit to Ala was 0.14 for diagnosis of NICCD, the sensitivity and specificity were 75% and 95% respectively.

CONCLUSIONThe plasma amino acid spectrum may represent a diagnostic indicator for NICCD, particularly the ratio of Cit to Ala.