Discovery of Causative Genetic Variants in Patients with Congenital and/or Developmental Anomalies by Exome...

Background/Objectives: Congenital anomalies and neurodevelopmental disorders frequently co-occur and exhibit substantial genetic and phenotypic heterogeneity, posing a persistent diagnostic challenge. Exome sequencing has become an important first- or second-tier diagnostic tool for these conditions, yet diagnostic yields vary considerably depending on phenotype, ancestry, sequencing strategy, and interpretation, with over half of referrals remaining without a definitive genetic diagnosis. Methods: We analyzed data from 692 patients referred to the Department of Cytogenetics and Genomics at the Cyprus Institute of Neurology and Genetics between January 2021 and December 2025 for clinical exome sequencing or whole-exome sequencing as part of the diagnostic work-up for congenital disorders and/or syndromic or non-syndromic neurodevelopmental disorders. Results: A total of 134 distinct variants were identified, corresponding to an overall diagnostic yield of 17.9% out of which 52 (38.8%) were novel, and 50 variants (37.3%) were de novo, as expected from the high proportion of severe neurodevelopmental presentations. Missense variants were the most prevalent within our cohort, while chromatin and transcriptional regulator genes constituted the largest functional gene category, followed by variants in collagen-encoding genes. Conclusions: This study provides the first systematic, mutational-level characterization of a Cypriot Mendelian disease cohort, establishing a local baseline diagnostic yield and revealing a high proportion of novel variants that reflect the underrepresentation of Eastern Mediterranean populations in global databases. These findings underscore the value of submitting population-specific variants to public repositories and of phenotype-driven reanalysis targeting recurrent gene families, supporting more efficient diagnostics and future precision medicine initiatives in Cyprus.