Exome Sequencing Diagnoses X-Linked Moesin-Associated Immunodeficiency in a Primary Immunodeficiency Case

Abstract

BackgroundWe investigated the molecular etiology of a young male proband with confirmed immunodeficiency of unknown cause, presenting with recurrent bacterial and Varicella zoster viral infections in childhood and persistent lymphopenia into early adulthood.AimTo identify causative functional genetic variants related to an undiagnosed primary immunodeficiency.MethodWhole genome microarray copy number variant (CNV) analysis was performed on the proband followed by whole exome sequencing (WES) and trio analysis of the proband and family members. A >4 kbp deletion identified by repeated CNV analysis of exome sequencing data along with three damaging missense single nucleotide variants were validated by Sanger sequencing in all family members. Confirmation of the causative role of the candidate gene was performed by qPCR and Western Blot analyses on the proband, family members and a healthy control.ResultsCNV identified our previously reported interleukin 25 amplification in the proband; however, the variant was not validated to be a candidate gene for immunodeficiency. WES trio analysis, data filtering and in silico prediction identified a novel, damaging (SIFT: 0; Polyphen 1; Grantham score: 101) and disease-causing (MutationTaster) single base mutation in the X chromosome (c.511C > T p.Arg171Trp) MSN gene not identified in the UCSC Genome Browser database. The mutation was validated by Sanger sequencing, confirming the proband was hemizygous X-linked recessive (–/T) at this locus and inherited the affected T allele from his non-symptomatic carrier mother (C/T), with other family members (father, sister) confirmed to be wild type (C/C). Western Blot analysis demonstrated an absence of moesin protein in lymphocytes derived from the proband, compared with normal expression in lymphocytes derived from the healthy control, father and mother. qPCR identified significantly lower MSN mRNA transcript expression in the proband compared to an age- and sex-matched healthy control subject in whole blood (p = 0.02), and lymphocytes (p = 0.01). These results confirmed moesin deficiency in the proband, directly causative of his immunodeficient phenotype.ConclusionThese findings confirm X-linked moesin-associated immunodeficiency in a proband previously undiagnosed up to 24 years of age. This study also highlights the utility of WES for the diagnosis of rare or novel forms of primary immunodeficiency disease.

Hematopoietic Stem Cell Transplant for the Treatment of X-MAID

“…Six out of seven patients have been managed with prophylactic antibiotic treatment and immunoglobulin replacement and, in one case, chronic G-CSF for neutropenia. There have been two additional cases of X-MAID published (9, 10). In one of these, similar to ours, profound lymphopenia was detected in follow up testing to an abnormal SCID NBS (9).…”

Human inborn errors of the actin cytoskeleton affecting immunity: way beyond WAS and WIP

“…The MSN gene is located on the X chromosome. MSN LOF mutations leading to moesin deficiency (OMIM 300988) have been reported in hemizygous males who suffered from combined immunodeficiency, characterized by early onset recurrent bacterial infections of the skin and the respiratory, urinary and gastrointestinal tracts, severe and recurrent VZV infection and persistent moderate eczema . The patients had thrombocytopenia, persistent T, B and NK lymphopenia, fluctuating monocytopenia and neutropenia and hypogammaglobulinemia.…”

“…However, present thymic shadow and normal proliferation to phytohemagglutinin argued against typical SCID . Of nine patients from seven kindreds described so far, eight carry the same missense mutation (c.511C>T, R171W) and one a nonsense mutation (c.1657C>T, R553X) . The R171W variant resulted in a relative decrease of MSN+ T cells over time, at least in the single patient in whom sequential samples were analyzed while expression was preserved in the other blood cell lines.…”

Primary immunodeficiencies caused by mutations in actin regulatory proteins

“…The MSN gene is on the X chromosome. Two reports describe several boys with frequent bacterial and varicella infections having mutations in the MSN gene . They had decreased naive T cells with reduced proliferation and an increase in the CD57 senescence marker.…”

“…Two reports describe several boys with frequent bacterial and varicella infections having mutations in the MSN gene. 187,188 They had decreased naive T cells with reduced proliferation and an increase in the CD57 senescence marker. While MSN deficient T cells were able to form an IS with Raji B cell, they had decreased chemokine receptor and adhesion marker expression along with decreased in vitro migration to the chemokines CCL21 and SDF1α.…”