Mutation characterization and heterodimer analysis of patients with leukocyte adhesion deficiency: Including one novel mutation

BACKGROUND AND AIM

Leukocyte adhesion deficiency type 1 (LAD-I) is a rare, autosomal recessive disorder of neutrophil migration, characterized by severe, recurrent bacterial infections, inadequate pus formation and impaired wound healing. The ITGB2 gene encodes the β2 integrin subunit (CD18) of the leukocyte adhesion cell molecules, and mutations in this gene cause LAD-I. The aim of the current study was to investigate the mutations in patients diagnosed with LAD-I and functional studies of the impact of two previously reported and a novel mutation on the expression of the CD18/CD11a heterodimer.

MATERIALS AND METHODS

Blood samples were taken from three patients who had signed the consent form. Genomic DNA was extracted and ITGB2 exons and flanking intronic regions were amplified by polymerase chain reaction. Mutation screening was performed after Sanger sequencing of PCR products. For functional studies, COS-7 cells were co-transfected with an expression vector containing cDNA encoding mutant CD18 proteins and normal CD11a. Flow cytometry analysis of CD18/CD11a expression was assessed by dimer-specific IB4 monoclonal antibody.

RESULTS

Two previously reported mutations and one novel mutation,p. Cys562Tyr, were found. All mutations reduced CD18/CD11 heterodimer expression.

CONCLUSION

Our strategy recognized the p.Cys562Tyr mutation as a pathogenic alteration that does not support CD18 heterodimer formation. Therefore, it can be put into a panel of carrier and prenatal diagnosis programs.

ATM Gene Mutations Detection in Iranian Ataxia-Telangiectasia Patients

Ataxia-Telangiectasia (AT) is an autosomal recessive disorder involving cerebellar degeneration, immunodeficiency, radiation sensitivity and cancer predisposition. The ATM gene on human chromosome 11q22.3 has recently been identified as the gene responsible for ataxia-telangiectasia (AT). The gene mutated in AT, which has been designated as the ATM gene, encodes a large protein kinase with a PI-3 kinase-related domain. More than 100 mutations are broadly distributed throughout the ATM gene. The large size of the ATM gene (66 exons spanning ~150kb of genomic DNA) together with the diversity and broad distribution of mutations in AT patients, greatly limits the utility of direct mutation screening as a diagnostic tool. In this study, 20 families with at least one affected child clinically suspected to have ataxia-telangiectasia were examined and their DNA was extracted and amplified with standard methods. Sequencing methods were used to detect the new point mutation. Four exons which were hot spots for point mutations in ATM gene were detected by PCR-SSCP or PCR-RFLP.

Comparison of two proliferation assays MTT and ltt in immunodeficient patients

MTT assay is designed for spectrophotometric quantification of cell growth and viability without using the radiactive isotopes. The aim of this study is comparison of LIT and MTT as sensitive poliferation assays in imrnunodeficient patients. 20 immunodeficient and 20 healthy subjects were selected in this study. All of them had normal lymphocytes count, normal CD3 and negative DIR reaction to PPD, DT and candida. The immunodeficient patients regularly suffered from herpes, candida and staph abscess. The lymphocytes of inimunodeficient control groups were treated with PHA as mitogen. The lymphocyte proliferation was evaluated by MTT and LTT. The results showed a strong correlation between LTT and MITT between immunodeficient patients and healthy controls. The sensitivity test for MTT was 90%, and the sensitivity test for LTT was 98%. MTT method can be considered as a non-radiactive evaluation of cell proliferation. Detecting cell proliferation with accurate, sensitive, fast, easy and safe method is more preferable than LTT.

Use of D11S2179 and D11S1343 as markers for prenatal diagnosis of ataxia telangiectasia in Iranian patients

Ataxia telangiectasia (AT) is an autosomal recessive disorder with an estimated prevalence of 1/40,000 to 1/100,000 in reported populations. There is a 25% possibility for having an affected child when parents are carriers for the ATM gene mutation. There is no cure available for this disease and prenatal testing is strongly recommended for prevention of this disease. Although the preferred method is the direct mutation analysis of the ATM gene, the large size of the ATM gene with 63 exons and the large number of possible mutations in patients considerably limit efficiency of mutation analysis as a diagnostic choice. Indirect method is a better tool when parents are not carriers of founder mutation and pass different mutations to their children. Indirect molecular diagnosis using ATM-related molecular markers facilitates prenatal diagnosis of AT children. In this study, four molecular markers: D11S2179, D11S1787, D11S535, D11S1343 are genotyped in 19 unrelated families from different regions of Iran. Those markers are amplified using extracted sequence primers from the Gene Bank with their described PCR conditions. Amplified products were separated using denaturing PAGE gels, and data were analyzed to detect their pattern of inheritance in each family. In all families, segregation of alleles was according to Mendelian inheritance, and affected chromosomes were distinguishable from unaffected ones. All carriers and affected patients were diagnosed accurately. Thus, this method is effectively useful in prenatal diagnosis of AT.

DNA banking of primary immunodeficiency disorders in iran

Primary immunodeficiency disorders are a heterogeneous group of genetic disorders, with different modes of inheritance, consisting of more than 100 different types. We constructed the DNA banking of primary immunodeficiency disorders for the first time in Iran. The DNA of 31 immunodeficient patients and their families (total of 92 samples) were collected, as the first step for construction of DNA banking. DNA was isolated from whole blood by salting out method. Among our patients, Common variable immunodeficiency was the most common disorder, followed by X-linked agammaglobulinemia, Ataxia-telangiectasia, Chronic granulomatous disease, Severe combined immunodeficiency, Hyper IgM syndromes, and Leukocyte adhesion defects. DNA banking is a useful method for further detection of mutation in immunodeficient patients and prenatal diagnosis for presence or absence of the disorder in the fetus which can be confirmed by molecular genetics testing.