MSACL 2025 Abstract

Transferrin Analysis versus Glycomics in Congenital Disorders of Glycosylation Testing

Matthew J Schultz, Kris Liedtke, Coleman Turgeon, Dietrich Matern, Patricia L. Hall
Mayo Clinic Biochemical Genetics Laboratory, Rochester MN 55905

Matthew Schultz (Presenter) Mayo Clinic

Relevant Financial Disclosures (within past 24 months, reported on Jul 17, 2025) No relevant financial relationship(s) to disclose. Conflict mitigation NOT REQUIRED.

INTRODUCTION:
Congenital disorders of glycosylation (CDG) are a heterogeneous group of rare genetic conditions that present with a broad clinical spectrum. For CDG affecting N-linked glycosylation, transferrin glycosylation analysis performed by a variety of methods has been the cornerstone of biochemical testing. More recently, glycomics approaches have become available in clinical laboratories. In this study, we retrospectively evaluated the incremental diagnostic utility of glycomics testing compared to transferrin analysis alone across a range of CDG conditions in our laboratory.

METHODS:
Combined transferrin and ApoCIII glycoform analysis is performed by intact protein analysis using online immunoaffinity enrichment (via an in-house produced column), followed by electrospray ionization mass spectrometry (ESI-MS) on a SCIEX X500B QTOF high-resolution instrument. Spectra are deconvoluted to a single charge state profile and major glycoform ratios are reported along with qualitative profile assessment of any abnormal glycoforms present. Glycomics analysis entails overnight PNGase F–mediated glycan release, graphitized carbon enrichment, permethylation, and analysis using a SCIEX 5800 MALDI-TOF instrument. Glycomic profiles are reviewed and assessed utilizing Collaborative Integrative Laboratory Reports (CLIR) multivariate pattern recognition software. Results were reviewed from January 2022 to April 2025 and includes 10,484 transferrin/ApoCIII tests with 421 having combined glycomic analysis also performed.

RESULTS:
Of cases analyzed by intact protein analysis, 552 samples demonstrated elevated mono-glycosylated transferrin ratio (type I pattern) and 211 samples demonstrated an elevated ratio of a glycan lacking sialic acid (trisialo; type II pattern). Among cases with both transferrin and glycomics data available, both tests were abnormal in 48 samples. Notably, for known individuals with PMM2-CDG, the most prevalent subtype (representing 60–70% of CDG cases in the literature), transferrin and glycomics were both abnormal in all cases (n=18). Three diagnostic samples were identified by glycomics alone (SLC35C1-CDG (2) and MOGS-CDG(1)) while glycomic analysis suggested abnormalities in four additional individuals in which outcomes could not be confirmed.

CONCLUSION:
Transferrin glycoform analysis remains a valuable first-tier screening method for N-linked CDG. Transferrin and glycomic analysis provide complementary information for many conditions and glycomic analysis enhances detection of several CDG including SLC35C1-CDG and MOGS-CDG. Further studies are warranted to outline the role of glycomics in specific diagnostic contexts.