Novel mutations of ITGB2 induced leukocyte adhesion defect type 1

Abstract

Objective: To investigate the pathogenic mechanism of two novel ITGB2 mutations in leukocyte adhesion defect type 1 (LAD1). Methods: The clinical history and blood sample of an 11 years old patient admitted to Affiliated Hospital of Qingdao University in August 2014 were collected. Expression of CD18 (encoded by ITGB2) was analyzed by flow cytometry. Novel ITGB2 mutations were identified by next-generation sequencing technology and confirmed by Sanger sequencing. The functional effect of ITGB2 mutations was detected by PolyPhen2. Expression vectors of both wild type and mutant ITGB2 were constructed and transfected into mammalian cells for analysis of protein stability and subcellular location. Results: The symptoms of the patient (recurrent infections, lowered alveolar ridge and hypodontia) supported the diagnosis of LAD1. Expression of CD18 on the leukocytes was significantly decreased (0.2%) compared with the control samples from the parents (paternal: 99.0%; maternal: 99.1%). The patient was identified to be compound heterozygous for ITBG2 c.954del G (novel mutation) and c.1802C>A (paternal originated). ITGB2 c.954 del G was confirmed to be a harmful frameshift mutation; ITGB2 c.1802C>A was also predicted to be harmful. In terms of protein stability. There was no significant difference between mutant D18 and wild type. However, subcellular location analysis showed the mutant D18 could not locate on cell membrane. Conclusion: The compound heterozygous of ITGB2 mutations (c.954del G and c.1802C>A) decreases the expression and impairs the location of CD18 on leukocytes, which leads to LAD1.