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.

Fast screening of N-glycosylation disorders by sialotransferrin profiling with capillary zone electrophoresis.

Background Congenital disorders of glycosylation (CDG) are a growing group of rare genetic disorders. The most frequently used screening method is sialotransferrin profiling using isoelectric focusing (IEF). Capillary zone electrophoresis (CZE) may be a simple and fast alternative. We investigated the Capillarys™ CDT assay (Sebia, France) to screen for N-glycosylation disorders, using IEF as gold standard. Methods Intra- and inter-assay precision were established, and analyses in heparin-anticoagulated plasma and serum were compared. Accuracy was assessed by comparing IEF and CZE profiles of 153 samples, including 49 normal, 53 CDG type I, 2 CDG type II, 1 combined CDG type I and type II and 48 samples with a Tf-polymorphism. Neuraminidase-treated plasma was analysed to discriminate CDG and Tf-polymorphisms using samples of 52 subjects (25 had a confirmed Tf-polymorphism). Age-dependent reference values were established using profiles of 312 samples. Results Heparin-plasma is as suitable as serum for CDG screening with the Capillarys™ CDT assay. The precision of the method is high, with a limit of quantification (LOQ) of 0.5%. All profiles, including CDG and Tf-polymorphisms, were correctly identified with CZE. Forty-nine of 52 neuraminidase-treated samples correctly identified the presence/absence of a Tf-polymorphism. Interferences in 3/52 samples hampered interpretation. Sialo-Tf profiles were dependent of age, in particular in the first three months of age. Conclusions CZE analysis with the Capillarys™ CDT kit (Sebia) is a fast and reliable method for screening of N-glycosylation defects. Tf-polymorphisms could be excluded after overnight incubation with neuraminidase.