Triple diagnosis of Wiedemann‐Steiner, Waardenburg and DLG3‐related intellectual disability association found by WES: A case report

Background The development of whole‐exome sequencing (WES) and whole‐genome sequencing (WGS) for clinical purposes now allows the identification of multiple pathogenic variants in patients with a rare disease. This occurs even when a single causative gene was initially suspected. We report the case of an 8‐year‐old patient with global developmental delays and dysmorphic features, with a possibly pathogenic variant in three distinct genes. Methods Trio‐based exome sequencing was performed by IntegraGen SA (Evry, France), on an Illumina HiSeq4000 (Illumina, San Diego, CA, USA). Sanger sequencing was performed to confirm the variants that were found. Results WES showed the presence of three possibly deleterious variants: KMT2A: c.9068delA;p.Gln3023Argfs*3 de novo, PAX3: c.530C>G;p.Ala177Gly de novo and DLG3: c.127delG;p.Asp43Metfs*22 hemizygous inherited from the mother. KMT2A pathogenic variants are involved in Wiedemann‐Steiner syndrome, and PAX3 is the gene responsible for Waardenburg syndrome. DLG3 variants have been described in a non‐syndromic X‐related intellectual disability. Conclusions Considering the dysmorphic features and intellectual disability presented by this patient, these three variants were imputed as pathogenic and their association was considered responsible for his phenotype. Dual molecular diagnoses have already been found by WES in several cohorts with an average of diagnostic yield of 7%. This case demonstrates and reminds us of the importance of analyzing exomes rigorously and exhaustively because, in some cases (< 10%), it can explain superimposed traits or blended phenotypes.