Trio‐WES reveals a novel de novo missense mutation of KMT2A in a Chinese patient with Wiedemann‐Steiner syndrome: A case report

Background Wiedemann‐Steiner Syndrome (WSS) is an autosomal dominant genetic condition caused by mutations in the KMT2A gene. Lysine methyltransferase, encoded by KMT2A , plays critical roles in the regulation of gene expression during early development. Methods Trio‐based whole exome sequencing (Trio‐WES) was performed on a 15 months old Chinese girl and her two parents by MyGenostics (Beijing, China) using the Illumina HiSeq X ten system. Variants were confirmed with Sanger sequencing. She exhibited mild/moderate intellectual disability (ID), hypotonia, hypertrichosis cubiti, hypertrichosis on the back, dysmorphic facies, psychomotor retardation, growth delay, small and puffy hands, fat pads anterior to calcanei, and palmar/plantar grooves. Results Trio‐WES revealed a novel de novo mutation of KMT2A gene (NM_001197104.1: c.3566G>T, p.Cys1189Phe). WSS was diagnosed based on WES and clinical features. Conclusion Our findings expand the phenotypic and mutation spectra of WSS.