Maleic acid is a biomarker for maleylacetoacetate isomerase deficiency; implications for newborn screening of tyrosinemia type 1.

Dried blood spot succinylacetone (SA) is often used as a biomarker for newborn screening (NBS) for tyrosinemia type 1 (TT1). However, false-positive SA results are often observed. Elevated SA may also be due to maleylacetoacetate isomerase deficiency (MAAI-D), which appears to be clinically insignificant. This study investigated whether urine organic acid (uOA) and quantitative urine maleic acid (Q-uMA) analyses can distinguish between TT1 and MAAI-D. We reevaluated/measured uOA (GC-MS) and/or Q-uMA (LC-MS/MS) in available urine samples of nine referred newborns (2 TT1, 7 false-positive), eight genetically confirmed MAAI-D children, and 66 controls. Maleic acid was elevated in uOA of 5/7 false-positive newborns and in the three available samples of confirmed MAAI-D children, but not in TT1 patients. Q-uMA ranged from not detectable to 1.16 mmol/mol creatinine in controls (n = 66) and from 0.95 to 192.06 mmol/mol creatinine in false-positive newborns and MAAI-D children (n = 10). MAAI-D was genetically confirmed in 4/7 false-positive newborns, all with elevated Q-uMA, and rejected in the two newborns with normal Q-uMA. No sample was available for genetic analysis of the last false-positive infant with elevated Q-uMA. Our study shows that MAAI-D is a recognizable cause of false-positive TT1 NBS results. Elevated urine maleic acid excretion seems highly effective in discriminating MAAI-D from TT1.

Combined LDI/SAT test to evaluate intestinal lactose digestion and mucosa permeability.

BACKGROUND: Intestinal mucosal damage causes impaired digestive capacity and increased mucosal permeability. Quantification of damage can be used to improve treatment options. Currently, the Lactose Digestion Index (LDI) and the Sugar Absorption Test (SAT) are used for evaluation. The investigation studied whether both tests could be combined to provide a useful multifunctional test and whether measurements in blood (LDI) could be replaced by measurements in urine. MATERIALS AND METHODS: The LDI (25 g 13C-lactose, 0.5 g 2H-glucose), the SAT (5 g lactulose, 1 g L-rhamnose) and the LDI/SAT combination test were performed in seven lactose-digesting and eight lactose-maldigesting adults. Plasma glucose 13C-enrichment was determined by gas-chromatography/combustion/isotope ratio mass-spectrometry (GC/C/IRMS), 2H enrichment determined by gas-chromatography/mass-spectrometry (GC/MS) and urinary sugars by gas-chromatography (GC). RESULTS: The results of the separate LDI test were not different from those of the LDI/SAT in the lactose-digester group (0.82 +/- 0.06 vs. 0.81 +/- 0.09), nor in the lactose-maldigester group (0.36 +/- 0.12 vs. 0.35 +/- 0.06). A significant correlation was found between the 10-h urinary-lactose/lactulose ratio and the LDI (R2 = 0.71, P < 0.01). There were no differences in the lactulose/L-rhamnose ratio between lactose-digesters and lactose-maldigesters using both the SAT and LDI/SAT tests. CONCLUSION: The LDI/SAT test is a reliable method of measuring digestion and permeability simultaneously. The 10-h period urinary lactose/lactulose excretion ratio following lactose consumption reflects lactose digestive capacity.

Hereditary tyrosinaemia type I: a long-term study of the relationship between the urinary excretions of succinylacetone and delta-aminolevulinic acid.

Patients with hereditary tyrosinaemia type I (HT) excrete large amounts of succinylacetone (SA) in urine. Owing to structural resemblance of SA to delta-aminolevulinic acid (ALA), SA inhibits the second enzyme in the pathway for haeme biosynthesis, porphobilinogen synthase, resulting in increased urinary ALA excretion. We investigated the relationship between urinary SA and ALA excretions of two patients with different forms of HT (late-infantile and juvenile). In both patients the urinary SA and ALA excretions showed a more or less inverse correlation. The patient with the early-infantile form of HT had a relatively greater increase in urinary SA and ALA excretions in comparison to the patient with the juvenile form of HT. A possible explanation for this unexpected inverse correlation between the urinary excretion of SA and ALA might be a lack of intramitochondrial glycine, a substrate for delta-aminolevulinic acid synthesis. It has been reported previously that high concentrations of SA reversibly and competitively inhibit the transport of glycine through membranes.

Stable isotope dilution analysis of cystine in granulocyte suspensions as cysteine: a powerful method for the diagnosis, the follow-up, and treatment of patients with cystinosis.

A stable isotope dilution method was developed for the determination of cystine in granulocytes. Granulocytes were isolated from blood samples of treated cystinosis patients. Cystine in the granulocyte suspension was decoupled from proteins and converted to cysteine by treatment with a tri-butyl phosphine solution. Tertiary butyldimethyl silyl derivatives were prepared and analyzed by gas chromatography/mass spectrometry. Selective ion monitoring was carried out at m/z 304.3 (M-159 and m/z 406.4 (M-57) for the natural, and at m/z 306.3 and 408.4 for the labelled compound. [3,3,3',3'-2H]-DL-cystine was used as internal standard for the isotope dilution analysis. Concentrations of cystine in granulocytes could be accurately measured. There was a distinct difference in cystine concentrations in healthy individuals and treated patients.