John Capra
Last active: 3/3/2020

IgG4-related disease: Association with a rare gene variant expressed in cytotoxic T cells.

Newman JH, Shaver A, Sheehan JH, Mallal S, Stone JH, Pillai S, Bastarache L, Riebau D, Allard-Chamard H, Stone WM, Perugino C, Pilkinton M, Smith SA, McDonnell WJ, Capra JA, Meiler J, Cogan J, Xing K, Mahajan VS, Mattoo H, Hamid R, Phillips JA, Undiagnosed Disease Network
Mol Genet Genomic Med. 2019 7 (6): e686

PMID: 30993913 · PMCID: PMC6565556 · DOI:10.1002/mgg3.686

BACKGROUND - Family screening of a 48-year-old male with recently diagnosed IgG4-related disease (IgG4-RD) revealed unanticipated elevations in plasma IgG4 in his two healthy teenaged sons.

METHODS - We performed gene sequencing, immune cell studies, HLA typing, and analyses of circulating cytotoxic CD4+ T lymphocytes and plasmablasts to seek clues to pathogenesis. DNA from a separate cohort of 99 patients with known IgG4-RD was also sequenced for the presence of genetic variants in a specific gene, FGFBP2.

RESULTS - The three share a previously unreported heterozygous single base deletion in fibroblast growth factor binding protein type 2 (FGFBP2), which causes a frameshift in the coding sequence. The FGFBP2 protein is secreted by cytotoxic T-lymphocytes and binds fibroblast growth factor. The variant sequence in the FGFBP2 protein is predicted to form a disordered random coil rather than a helical-turn-helix structure, unable to adopt a stable conformation. The proband and the two sons had 5-10-fold higher numbers of circulating cytotoxic CD4 + T cells and plasmablasts compared to matched controls. The three members also share a homozygous missense common variant in FGFBP2 found in heterozygous form in ~40% of the population. This common variant was found in 73% of an independent, well characterized IgG4-RD cohort, showing enrichment in idiopathic IgG4-RD.

CONCLUSIONS - The presence of a shared deleterious variant and homozygous common variant in FGFBP2 in the proband and sons strongly implicates this cytotoxic T cell product in the pathophysiology of IgG4-RD. The high prevalence of a common FGFBP2 variant in sporadic IgG4-RD supports the likelihood of participation in disease.

© 2019 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc.

MeSH Terms (9)

Adolescent CD4-Positive T-Lymphocytes Genetic Variation Humans Immunoglobulin G Immunoglobulin G4-Related Disease Male Middle Aged T-Lymphocytes, Cytotoxic

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