The use of gene-specific classification guidelines VS ACMG 2015: MODY case study

Dario, Paulo; Vaz, Margarida; Gaspar, Gisela; Bourbon, Mafalda

http://hdl.handle.net/10400.18/8857

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Maturity Onset Diabetes of the Young (MODY) is a form of diabetes characterized as a dominant monogenic disorder. It is caused by pathogenic or likely pathogenic variants in any of the 14 genes currently associated with the disease. Since 2015 our laboratory has employed the classification algorithm guidelines established by the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG-AMP) for variant classification. However the process of variant classification under these guidelines can be intricate and time intensive. To address these limitations the Monogenic Diabetes Variant Classification Expert Panel (MDEP VCEP) has developed specialized guidelines for classifying MODY variants particularly those found in the GCK, HNF1A, and HNF4A genes. Our objective is to determine whether variants initially classified as VUS under the 2015 ACMG guidelines can achieve a definitive classification when re-evaluated using the specific criteria set forth by the MDEP guidelines. In this study we conducted a comparative analysis of two variants identified in patients from the Portuguese MODY Study: HNF1A c.599 G>A/(p.Arg200Gln) and GCK c.1268 T>A/p.(Phe423Tyr). The HNF1A variant was reclassified as Pathogenic, a decision influenced not only by the updated guidelines but also by collaborative data sharing between institutions This robust evidence included the number of affected individuals and their phenotypes, what lead to the upgrade of the variant classification. While the classification of the GCK variant remained VUS, it has not yet been curated by the MDEP group, so it is possible that a future re-evaluation with additional evidence can lead to a definitive classification. In conclusion, the implementation of disease specific guidelines has improved the precision of variant classification, as evidenced by the reclassification of at least one variant in our MODY Diabetes Study. The MDEP group continues to review and update variant classifications submitted to ClinVar sharing their findings.