It Is Not Always Alcohol Abuse--A Transferrin Variant Impairing the CDT Test.

AIMS: Elevated Carbohydrate-deficient transferrin (CDT) levels are used as a biomarker in order to screen for chronic alcohol abuse. Transferrin (Tf) variants can impair methods to measure elevated CDT levels such as high-performance liquid chromatography (HPLC). We present a Tf variant affecting the second glycosylation site of Tf and the complications it causes in diagnosing alcoholism. METHODS: A blood sample from a patient with suspected alcohol abuse was analyzed with HPLC, isoelectric focusing, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), immunoprecipitation and SDS-Page. Sanger sequencing of Tf was performed to detect Tf mutations. RESULTS: HPLC, SDS-Page and IEF showed a distinctly increased disialo-Tf fraction while the tetrasialo-Tf fraction was decreased, ESI-TOF-MS confirmed these results. Sanger sequencing revealed the Tf mutation c.1889 A>C, deleting a Tf glycosylations site and thereby causing elevated disialo-Tf levels. CONCLUSIONS: Transferrin mutations can severely impair the diagnostics of chronic alcohol abuse by causing false positive results. This has to be considered when CDT screening is used to detect alcoholism.

A Novel PKD1 Mutation Associated With Autosomal Dominant Kidney Disease and Cerebral Cavernous Malformation.

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by the presence of renal cysts and specific extrarenal abnormalities. ADPKD is caused by mutations in either PKD1 or PKD2 genes that encode for integral membrane proteins Polycystin-1 (PC1) and Polycystin-2 (PC2), respectively. Extrarenal involvement includes noncystic manifestations such as dilatation of the aortic root, artery dissection and intracranial aneurysms. Cerebral cavernous malformation (CCM) is a rare vascular malformation disorder characterized by closely clustered and irregularly dilated capillaries that can be asymptomatic or cause variable neurological manifestations, such as seizures, non-specific headaches, progressive or transient focal neurologic deficits, and cerebral hemorrhages. Familial CCM is typically associated with mutations in KRIT1 (CCM1), CCM2, and PDCD10 (CCM3). The co-occurrence of ADPKD and CCM has been previously described in a single patient, although genetic analysis was not performed in this study. We report here a family with ADPKD associated with CCM in two sisters. Direct sequencing of the index patient revealed a single novel heterozygous frameshift mutation in PKD1, and lack of mutations in genes usually related to CCM. This suggests that CCM represents an additional phenotype of ADPKD.

Limitations of galactose therapy in phosphoglucomutase 1 deficiency.

INTRODUCTION: Phosphoglucomutase 1 deficiency (PGM1 deficiency) has been identified as both, glycogenosis and congenital disorder of glycosylation (CDG). The phenotype includes hepatopathy, myopathy, oropharyngeal malformations, heart disease and growth retardation. Oral galactose supplementation at a dosage of 1 g per kg body weight per day is regarded as the therapy of choice. RESULTS: We report on a patient with a novel disease causing mutation, who was treated for 1.5 years with oral galactose supplementation. Initially, elevated transaminases were reduced and protein glycosylation of serum transferrin improved rapidly. Long-term surveillance however indicated limitations of galactose supplementation at the standard dose: 1 g per kg body weight per day did not achieve permanent correction of protein glycosylation. Even increased doses of up to 2.5 g per kg body weight did not result in complete normalization. Furthermore, we described for the first time heart rhythm abnormalities, i.e. long QT Syndrome associated with a glycosylation disorder. Mass spectrometry of IGFBP3, which was assumed to play a major role in growth retardation associated with PGM1 deficiency, revealed no glycosylation abnormalities. Growth rate did not improve under galactose supplementation. CONCLUSIONS: The results of our study indicate that the current standard dose of galactose might be too low to achieve normal glycosylation in all patients. In addition, growth retardation in PGM1 deficiency is complex and multifactorial. Furthermore, heart rhythm abnormalities must be considered when treating patients with PGM1 deficiency.

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.

The novel transferrin E592A variant impairs the diagnostics of congenital disorders of glycosylation.

BACKGROUND: The analysis of serum transferrin either by high-performance liquid chromatography (HPLC) or isoelectric focusing (IEF) is the standard diagnostic procedure in patients with the suspicion of a congenital disorder of glycosylation (CDG). Carbohydrate-deficient transferrin (CDT) is also analysed in monitoring programmes in cases of alcohol abuse. We report a novel transferrin variant that impairs the analysis using conventional methods and propose alternative forms of analysis. METHODS: Transferrin samples were analysed using HPLC, immunoprecipitation followed by SDS-PAGE and IEF. Neuraminidase treatment followed by conventional IEF and electrospray ionization time of flight mass spectrometry (ESI-TOF MS) were applied before sequencing of the transferrin gene was performed. RESULTS: The novel transferrin variant E592A, found both in homozygous and heterozygous form, causes an altered charge of the transferrin molecule, which changes the results of IEF and HPLC and mimics an increase in trisialo-transferrin. The change in charge can be detected either by neuraminidase digestion followed by IEF or by ESI-TOF MS. CONCLUSION: Conventional diagnostic methods for CDG are hindered by the novel transferrin E592A. Neuraminidase treatment followed by IEF and ESI-TOF MS can identify the mutation. The mutation appears to be functionally normal.