Evaluating DNA methylation episignatures as a first-tier diagnostic test in individuals with suspected genetic disorders.

DNA methylation (DNAm) episignature analysis is an emerging tool for diagnosing individuals with neurodevelopmental disorders, congenital anomalies, and growth disorders. We evaluated its clinical utility as a first-tier test in 62 individuals without prior molecular testing. DNAm arrays identified a diagnosis in 30.6% (19/62) of cases. The positivity rate was highest for Fragile X syndrome (100%, 5/5), followed by syndromic disorders (44%, 8/18) and imprinting disorders (25%, 6/24), including Silver-Russell, Beckwith-Wiedemann, and Prader-Willi syndromes. No diagnoses were made in 15 individuals with non-syndromic neurodevelopmental disorders. Alternative diagnoses were identified in 4.8% (3/62) of cases. These findings suggest that DNAm arrays can serve as an effective first-tier diagnostic tool, particularly for syndromic and imprinting disorders, with potential to improve diagnostic efficiency and reduce reliance on sequential genetic testing. While these findings support the use of DNAm arrays as an effective first-tier tool in selected populations, larger, unselected cohort studies are needed to validate its generalizability.