Immune dysfunction in MGAT2‐CDG: A clinical report and review of the literature

Abstract

Glycosylation is a critical post/peri‐translational modification required for the appropriate development and function of the immune system. As an example, abnormalities in glycosylation can cause antibody deficiency and reduced lymphocyte signaling, although the phenotype can be complex given the diverse roles of glycosylation. Human MGAT2 encodes N‐acetylglucosaminyltransferase II, which is a critical enzyme in the processing of oligomannose to complex N‐glycans. Complex N‐glycans are essential for immune system functionality, but only one individual with MGAT2‐CDG has been described to have an abnormal immunologic evaluation. MGAT2‐CDG (CDG‐IIa) is a congenital disorder of glycosylation (CDG) associated with profound global developmental disability, hypotonia, early onset epilepsy, and other multisystem manifestations. Here, we report a 4‐year old female with MGAT2‐CDG due to a novel homozygous pathogenic variant in MGAT2, a 4‐base pair deletion, c.1006_1009delGACA. In addition to clinical features previously described in MGAT2‐CDG, she experienced episodic asystole, persistent hypogammaglobulinemia, and defective ex vivo mitogen and antigen proliferative responses, but intact specific vaccine antibody titers. Her infection history has been mild despite the testing abnormalities. We compare this patient to the 15 previously reported patients in the literature, thus expanding both the genotypic and phenotypic spectrum for MGAT2‐CDG.

N-linked glycans: an underappreciated key determinant of T cell development, activation, and function

“…N-acetylglucosaminyltransferase-II, encoded by the Mgat2 gene, functions downstream of mannosidase-II and catalyzes the attachment of β1,2-N-acetylglucosamine to the α1,6-linked mannose residue to form biantennary decorated N-linked glycans and initiate the synthesis of complex N-linked glycans [58,59] (Figures 1 and 2). Point mutations in Mgat2 have been identified in humans and are associated with congenital disorder of glycosylation IIa and general neurological defects, as well as increased risk of experimental autoimmune encephalomyelitis in mice [58,[60][61][62] . Mice lacking Mgat2 exhibit severe developmental defects in various tissues and die early postnatally, indicating the critical role of complex N-linked glycans in regulating normal development and physiology [50,61] .…”