LAUSR

Dear Editor, Severe congenital neutropenia (SCN) is characterized by prolonged severe neutropenia (absolute neutrophil count < 500/μL) commencing in early infancy, and recurrent bacterial and/or fungal infections. Several mutations in genes including ELANE and HAX1 are known to cause SCN. However, the causative germline mutations remain to be elucidated in more than one-third of SCN patients [1]. X-linked neutropenia (XLN) is a very rare type of SCN caused by a gain-of-functionmutation in the Wiskott-Aldrich syndrome gene (WAS) located on the short arm of the X chromosome. To the best of our knowledge, only three WAS protein (WASP) mutations (L270P, S272P, and I294T) have been described to date [2–4]. Herein, we report the first Asian XLN case with a novel WASP mutation, which was successfully diagnosed by phenotype-based analysis of nextgeneration sequencing (NGS) data. A 29-year-old male visited our hospital for consultation. His history revealed that he had been clinically diagnosed with SCN at 6 years of age; however, he had not been scheduled for regular medical follow-up since then. His complete blood count (CBC) revealed a white blood cell (WBC) count of 1.3 × 10/μL, a hemoglobin level of 14.8 g/dL, and a platelet count of 127 × 10/μL. The WBC differential counts were as follows: 8% neutrophils, 5.3% monocytes, 2.3% eosinophils, 3% basophils, and 80.4% lymphocytes. Bone marrow examination revealed marked myeloid hypoplasia with a maturation arrest at the myelocyte stage. His family history revealed no significant evidence of inheritable SCN, but his mother’s peripheral blood exhibited slight neutropenia. The ELANE gene was subjected to Sanger sequencing but no mutation was found. We performed targeted exome sequencing of 4813 diseaserelevant genes using a TruSight One Sequencing Panel (Illumina, San Diego, CA); we prepared DNA from the peripheral blood of the patient and his mother. The sequencing data were analyzed in terms of somatic mutations using our inhouse pipeline, BGenomon^ (http://genomon.hgc.jp/exome/ en/) [5]. The resulting gene list, including 925 single nucleotide variants (SNVs), was subjected to examination by Phenolyzer (http://phenolyzer.usc.edu/) [6], a web-based computational tool that analyzes clinical phenotypes on the basis of free-text term(s) and predicts the most likely candidate gene(s) by integrating information from multiple databases. The terms entered were BCongenital neutropenia,^ BFamilial,^ BMyelodysplastic syndrome,^ and BAutosomal.^ Phenolyzer prioritized the WAS gene as the most probable candidate. Additionally, we identified a missense mutation in exon 9 of the patient’sWAS gene (c.T869C, p.I290T) using the Integrative Genomics Viewer (IGV) [7] (Fig. 1a, b). We also Masayuki Kobayashi and Kazuaki Yokoyama contributed equally to this work.