[Identification of a novel frameshift variant in the KMT2A gene of a child with Wiedemann-Steiner syndrome].

OBJECTIVE:To analyze pathogenic variant s of KMT2A gene in a child with Wiedemann-Steiner syndrome (WDSTS) and provide reliable evidences for clinical diagnosis of WDSTS. METHODS:Whole-DNAs were extracted from an 9 years-old boy and his parents. Trio-whole exome sequencing (trio-WES) was performed to identify candidate pathogenic variants that can explain the boy's condition and sanger sequencing was conducted to prove it. The impact of detected variants were predicted and validated by bioinformatics tools. RESULTS:A de novo frameshift variant c.10488dupG (p.Leu3498Thrfs*41) in exon 27 of KMT2A gene was detected and this de novo variant (PS2) had not been reported in the world previously. This frameshift variant was absent in major allele frequency databases (PM2) and had been predicted to be pathogenic based on MutationTaster. Through HomoloGene and CD-search system, the 3498 locus (Leu) in KMT2A protein, which was an important histone modifying enzyme that regulated gene expression in early embryonic development and encoded by the KMT2A gene, was predicted as a high conserved locus (PP3), and that replacement of Lue3498 may result in frame-shifts with premature termination in 3539 locus by introducing stop codon, causing deletion of multiple functional domains which all played important roles on histone modifications and recognition (PVS1+PM1). According to the American College of Medical Genetics and Genomics variant classification guideline, the variant c.10488dupG (p.Leu3498Thrfs*41) in KMT2A was classified as pathogenic variant (PVS1+PS2+PM1+PM2+PP3). CONCLUSION:The patient's condition may be attributed to the de novo frameshift variant c.10488dupG (p.Leu3498Thrfs*41) in KMT2A gene. This study reported a pathogenic KMT2A variant that had not been reported previously in WDSTS, it expanded the genotypic spectrums of KMT2A variants.