Use of a rare disease registry for establishing phenotypic classification of previously unassigned GLA variants: a consensus classification system by a multispecialty Fabry disease genotype-phenotype workgroup

• Type of Material: Article
• Authors: Dominique Germain, Universite Paris Saclay; Joao Paulo Oliveira, University of Porto; Daniel G. Bichet, University of Montreal; Han-Wook Yoo, University of Ulsan; Robert J. Hopkin, Cincinnati Childrens Hospital Medical Center; Roberta Lemay, Sanofi Genzyme; Juan Politei, Fdn Estudio Enfermedades Neurometab FESEN; Christoph Wanner, University of Wurzburg; William Wilcox, Emory University; David G. Warnock, University of Alabama Birmingham
• Language: English
• Date: 2020-08-01
• Publisher: BMJ Publishing Group
• Publication Version: Final Published Version
• Copyright Statement: © Author(s) (or their employer(s)) 2020.
• License: Creative Commons Attribution-NonCommercial 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1136/jmedgenet-2019-106467
• Title of Journal or Parent Work: Journal of Medical Genetics
• Volume: 57
• Issue: 8
• Start Page: 542
• End Page: 551
• Grant/Funding Information: DPG was supported by the Plan National Maladies Rares of the French Ministry of Health.; The authors received editorial/writing support in the preparation of this manuscript from Tom Rouwette of Excerpta Medica, funded by Sanofi Genzyme, and Hans Ebels of Sanofi Genzyme.; This research was funded by Sanofi Genzyme, the sponsor of the Fabry Registry.
• Keywords: Galactosidase-A-gene; Genetics & Heredity; genetics; genotype-phenotype correlations; Fabry disease; Form; Science & Technology; expert opinion; Families; Point mutations; Hemizygotes; Identification; variants; Mutant alpha-galactosidase; Life Sciences & Biomedicine
• Research Categories: Health Sciences, Pharmacology; Biology, Genetics; Biology, Neuroscience

Abstract

Background Fabry disease (α-galactosidase deficiency) is an X-linked genetic disease caused by a variety of pathogenic GLA variants. The phenotypic heterogeneity is considerable, with two major forms, classic and later-onset disease, but adjudication of clinical phenotype is currently lacking for many variants. We aimed to determine consensus phenotypic classification for previously unclassified GLA variants from the GLA-specific fabry-database.org database. Methods A Fabry disease genotype–phenotype workgroup developed a five-stage iterative system based on expert clinical assessment, published literature and clinical evidence of pathogenicity using a 2-point scoring system based on clinical hallmarks of classic disease. Kaplan–Meier (KM) analysis of severe clinical event-free survival was used as final validation. Results were compared with those from web-based disease databases and in silico pathogenicity prediction programmes. Results Final consensus on classifications of ‘pathogenic’ was achieved for 32 of 33 GLA variants (26 ‘classic’ phenotype, 171 males; 6 ‘later-onset’ phenotype, 57 males). One variant remained of uncertain significance. KM curves were similar for the known fabry-database.org database phenotypes and when workgroup consensus classifications were added, and the curves retained the same separation between ‘classic’ and ‘later-onset’ phenotypes. Conclusion The iterative system implemented by a Fabry disease genotype–phenotype workgroup achieved phenotypic classifications for variants that were previously unclassified. Clinical pathogenicity associated with a particular GLA variant defined in affected males appears to have predictive value and also generally correlates with risk for affected females. The newly established classifications can be of benefit to the clinical care of Fabry patients harbouring these variants.