Ps1569 Common Single Nucleotide Polymorphism of Tmprss6 Determines Variation of Red Blood Cell Indices Found in Heterozygous Alpha‐thalassemia

Abstract

Background:Globally, many screening programs for severe thalassemia (thal) syndromes use red blood cell (RBC) indices; mean corpuscular volume (MCV) <80 fl and/or mean corpuscular hemoglobin (MCH) <25 pg as cut‐off to identify thal disease and carriers. These criterion seem to be sensitive for individual with α°‐thal by two α‐globin gene deletions (‐‐/αα) and β‐thal traits. However this approach cannot be used for confidential identification α+‐thal trait (‐α/αα) due to a wide variation of baseline MCV and MCH. Recently, a single nucleotide polymorphism (SNP) of an iron regulation gene; tmprss6 involved in substitution a nucleotide between thymine (T) and cytosine (C) in exon 17 resulted to amino acid change from valine to alanine (V736A) has been described to associate with RBC indices. However its role on thalassemic RBC remains largely unknown.Aims:To determine the effects of common SNP rs855791 of tmprss6 on RBC indices variation in deletional α‐thal carriersMethods:EDTA whole blood samples were collected from Thai healthy volunteers in cohort and measured complete blood count, RBC indices, hemoglobin typing and comprehensive molecular analysis panel covered > 98% of common globin mutations (α‐thal, β‐thal, Hb E) found in Thailand. SNP rs855791 genotypes of tmprss6 were analyzed by PCR‐RFLP with StuI restriction enzyme. Statistical analysis for average (mean), standard deviation (SD) and comparisons was performed by using PASW Statistics 18. The significant difference was determined by p ≤ 0.05.Results:Total 433 cases (age: 23.0 ± 8.7 years old, male: N = 141 (32.6%), female: N = 292 (67.4%)) of normal β‐globin gene (ββ) included three genotypes of α‐globin gene; normal (αα/αα) (N = 357, 82.4%), ‐α/αα (N = 61, 14.1%), and ‐‐/αα (N = 15, 3.5%) (Table 1). The allele frequency of SNP rs855791 of Thai population showed T:C as 0.6 to 0.4 that similar to other Asian population and consistent across different globin genotypes (Table2). The MCV and MCH ranges of two α‐globin genotypes; αα/αα and ‐α/αα showed an overlapping feature. Interestingly, we found no effect of either C or T polymorphism on RBC indices mainly MCV and MCH in individuals with normal globin genes. However the effects of SNP rs855791 genotypes on MCV and MCH were demonstrated in α‐thal traits. Increased MCV and MCH gradually expressed by SNP genotype C/C > C/T > T/T both in α+‐ and α°‐thal trait (Figure 1 and 2). Comparing the level of serum ferritin among different tmprss6 genotypes; the C/C seemed to have higher iron status followed by C/T and T/T, however there was no statistical significance (data not shown). Therefore this epistatic effect of tmprss6 on determining RBC indices in α‐thal carriers may operate through other mechanism.Summary/Conclusion:For the first time, we have identified that tmprss6 polymorphism can determine RBC size and hemoglobinization in carrier of α‐thal. The genetic mechanism of tmprss6 involved in the determination RBC indices in α‐thal mutations would be further studied.image