Screening for abnormal glycosylation in a cohort of adult liver disease patients.

Jos C Jansen,Karin Huijben,Joost P H Drenth,Aad P Van Den Berg,Fokje Zijlstra,Herold J Metselaar,Monique Van Scherpenzeel,Bart Van Hoek,Dirk J Lefeber

doi:10.1002/jimd.12273

Abstract

Congenital disorders of glycosylation (CDG) are a rapidly expanding group of rare genetic defects in glycosylation. In a novel CDG subgroup of vacuolar‐ATPase (V‐ATPase) assembly defects, various degrees of hepatic injury have been described, including end‐stage liver disease. However, the CDG diagnostic workflow can be complex as liver disease per se may be associated with abnormal glycosylation. Therefore, we collected serum samples of patients with a wide range of liver pathology to study the performance and yield of two CDG screening methods. Our aim was to identify glycosylation patterns that could help to differentiate between primary and secondary glycosylation defects in liver disease. To this end, we analyzed serum samples of 1042 adult liver disease patients. This cohort consisted of 567 liver transplant candidates and 475 chronic liver disease patients. Our workflow consisted of screening for abnormal glycosylation by transferrin isoelectric focusing (tIEF), followed by in‐depth analysis of the abnormal samples with quadruple time‐of‐flight mass spectrometry (QTOF‐MS). Screening with tIEF resulted in identification of 247 (26%) abnormal samples. QTOF‐MS analysis of 110 of those did not reveal glycosylation abnormalities comparable with those seen in V‐ATPase assembly factor defects. However, two patients presented with isolated sialylation deficiency. Fucosylation was significantly increased in liver transplant candidates compared to healthy controls and patients with chronic liver disease. In conclusion, a significant percentage of patients with liver disease presented with abnormal CDG screening results. However, the glycosylation pattern was not indicative for a V‐ATPase assembly factor defect. Advanced glycoanalytical techniques assist in the dissection of secondary and primary glycosylation defects.

Highlights

Congenital disorders of glycosylation (CDG) are a group of inborn errors of metabolism characterized by abnormal glycosylation
Supplementary table 1 shows transferrin isoelectric focusing (tIEF) and quadruple time-of-flight mass spectrometry (QTOF-MS) results for all samples with an abnormal tIEF profile. 3.1 tIEF screening of 961 samples of liver disease patients shows mild glycosylation abnormalities Out of 961 samples we analyzed using tIEF, 247 samples (26%) had hyposialylation compared to our controls
The mixed profiles can be compatible with a CDG type 2 profile, in most samples the increase in percentage is subtle (Figure 3b). 3.2 QTOF-MS analysis of preselected liver disease patients did not identify profiles compatible with V-ATPase assembly factor defects

Summary

Introduction

Congenital disorders of glycosylation (CDG) are a group of inborn errors of metabolism characterized by abnormal glycosylation. A novel subgroup of CDG patients has emerged that presents predominantly with a hepatic phenotype. The hepatic clinical spectrum ranges from mildly elevated serum transaminases and steatosis, resembling nonalcoholic fatty liver disease, to cirrhosis and end-stage liver disease warranting liver transplantation (LTx). The central pathological event in cirrhosis is deposition of extracellular matrix increasing hepatic flow resistance with ensuing hepatocyte dysfunction.(Tsochatzis et al 2014) Patients with cirrhosis have a high risk of decompensation of their liver disease. It can develop in end-stage liver disease (ESLD), necessitating (LTx)

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