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.

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.
Competing Interests: Competing interests: DPG is a consultant for Sanofi Genzyme and Takeda/Shire, was an investigator in clinical trials sponsored by Amicus Therapeutics and Sanofi Genzyme and has received speaker honoraria and travel support from Amicus Therapeutics, Sanofi Genzyme and Takeda/Shire. JPO has received consulting honoraria and unrestricted research grants and funding for research projects from Sanofi Genzyme, has received speaker honoraria from Sanofi Genzyme and Takeda/Shire and has received conference and travel support from Amicus Therapeutics, Sanofi Genzyme and Takeda/Shire. DGB has received speaker honoraria from Amicus Therapeutics, Sanofi Genzyme and Takeda/Shire. HWY has received honoraria from Sanofi Genzyme. RJH has received consulting honoraria from Sanofi Genzyme, Amicus Therapeutics, Protalix Corporation and Takeda/Shire, was an investigator in clinical trials sponsored by Amicus Therapeutics, Sanofi Genzyme and Takeda/Shire and received research funding from Sanofi Genzyme, Protalix Corporation and Amicus Therapeutics; these activities have been monitored and found to be in compliance with the conflict of interest policies at Cincinnati Children’s Hospital Medical Center. RL is an employee of Sanofi Genzyme. JP has received honoraria and travel support from Amicus Therapeutics, Protalix Corporation, Sanofi Genzyme and Takeda/Shire. CW has received research support from Sanofi Genzyme and is a consultant for Actelion Pharmaceuticals, Protalix Corporation, Boehringer Ingelheim GmbH and Sanofi Genzyme. WRW consults for Sanofi Genzyme and was an investigator in clinical studies and trials sponsored by Amicus Therapeutics, Protalix Corporation, Sanofi Genzyme and Takeda/Shire and has received research funding from Sanofi Genzyme, Amicus Therapeutics and Takeda/Shire; these activities are monitored and are in compliance with the conflict of interest policies at Emory University School of Medicine. DGW received consulting honoraria from Amicus Therapeutics, Sanofi Genzyme, Actelion Pharmaceuticals, AVROBIO, Freeline Therapeutics and Protalix Biotherapeutics and has received research funding from Amicus Therapeutics and Sanofi Genzyme. DPG, JPO, DGB, HWY, RJH, JP and CW are Regional or International Fabry Registry Board members and have received Fabry Registry Board honoraria.
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