DNA methylation episignature testing improves molecular diagnosis of Mendelian chromatinopathies

Chromatinopathies include more than 50 disorders caused by disease-causing variants of various components of chromatin structure and function. Many of these disorders exhibit unique genome-wide DNA methylation profiles, known as episignatures. In this study, the methylation profile of a large cohort of individuals with chromatinopathies was analyzed for episignature detection.DNA methylation data was generated on extracted blood samples from 129 affected individuals with the Illumina Infinium EPIC arrays and analyzed using an established bioinformatic pipeline.The DNA methylation profiles matched and confirmed the sequence findings in both the discovery and validation cohorts. Twenty-five affected individuals carrying a variant of uncertain significance, did not show a methylation profile matching any of the known episignatures. Three additional variant of uncertain significance cases with an identified KDM6A variant were re-classified as likely pathogenic (n = 2) or re-assigned as Wolf-Hirschhorn syndrome (n = 1). Thirty of the 33 Next Generation Sequencing negative cases did not match a defined episignature while three matched Kabuki syndrome, Rubinstein-Taybi syndrome and BAFopathy respectively.With the expanding clinical utility of the EpiSign assay, DNA methylation analysis should be considered part of the testing cascade for individuals presenting with clinical features of Mendelian chromatinopathy disorders.