Transferrin variants: pitfalls in the diagnostics of Congenital disorders of glycosylation.

OBJECTIVES: Transferrin variants can hinder the diagnostic process in cases of suspected Congenital disorders of glycosylation which affect N-Glycosylation. In addition they can impair the use of Carbohydrate deficient Transferrin as a biomarker for chronic alcohol abuse, in which Asialo-Transferrin and Disialo-Transferrin are increased. We present a novel transferrin variant as well as an overview of transferrin mutations found at our laboratory. DESIGN AND METHODS: Blood samples from patients with suspected CDG were analyzed using the standard diagnostic procedures of Isoelectric focusing and High-performance liquid chromatography as well as the additional procedures of neuraminidase digestion of glycans and Electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS). RESULTS: Four known and one previously unreported transferrin variants were identified. Neuraminidase digestion and ESI-TOF MS revealed changes in charge of the transferrin molecules while the glycosylation status was found to be normal. CONCLUSION: Transferrin variants are pitfalls in the diagnostics of CDG. The found variants change the charge of the transferrin molecule, thus affecting the standard diagnostic procedures. Neuraminidase digestion as well as ESI-TOF MS can identify variants and mutations in a laboratory context.