A small scale study evaluating allelic frequencies of human neutrophil antigens in Hong Kong Chinese population

Abstract

Background: Human neutrophil antigens (HNA) are involved in a variety of clinical conditions such as transfusion related acute lung injury (TRALI), alloimmune neutropenia (ANN), autoimmune neutropenia (AIN). There are a total of five HNA systems, namely HNA-1, HNA-2, HNA-3, HNA-4 and HNA-5. In this decade, the allelic and genotypic frequencies of HNA were gradually evaluated in Europe, America and East Asia. [1] Despite HNA system being less polymorphic than HLA antigens, genotypic and allelic frequencies differences can still be observed in different geographical locations even of close proximity. For instance, studies in Thailand and China displayed genotypic and allelic frequencies differences. [2] These data highlights the fact that HNA genotypic and allelic frequencies vary among different populations even within the same region, however, the degree of variation remains to be elucidated. However, there is no information on HNA genotypic and allelic frequencies of Hong Kong population. Commercial genotyping kit has been available in the market but given its high reagent cost, it is not very popular in clinical laboratory. For this reason, a comparative affordable and economical in-house PCR-SSP assay was developed in this study. Aim The aim of this study is to evaluate the HNA genotyping and allelic frequencies in Hong Kong Chinese population by the development of an economical in-house PCR-SSP assay. Methods A commercial HNA typing kit was tested with reference samples to ensure this project has a standard and clinical compliance method for HNA genotyping prior to adopting in-house genotyping method. After reference protocol was established, in-house primers were designed and tested in parallel with the commercial method for validation purpose. After in-house method has been validated, 113 local samples were tested to calculate the genotype and allele frequencies in Hong Kong Chinese population using the developed in-house assay. Results A total of 113 Hong Kong Chinese samples were typed for HNA genotyping and results shown that: HNA-1a was 0.664; HNA-1b was 0.336; whereas HNA-1c allele was not detected. HNA-3a was 0.735 and HNA-3b was 0.265. HNA-4a was 0.991 and HNA-4b was 0.009. HNA-5a was 0.845 and HNA-5b was 0.155. Overall, results echoed with an earlier study performed on Han Chinese. [3] The genotyping frequency distribution for HNA-1, 3, 4 and 5 were: HNA-1a/a was 0.451, HNA-1 b/b was 0.124 and HNA-1 a/b was 0.425; HNA-3 a/a was 0.549, HNA-3a/b was 0.372 and HNA-3b/b was 0.08; HNA-4a/a was 0.982, HNA-4a/b was 0.018; HNA-5a/a was 0.708, HNA-5a/b was 0.274 and HNA-5b/b was 0.018. Conclusion This is the first study attempted to define HNA genotype and allelic frequencies by the self-developed in-house PCR-SSP method in Hong Kong Chinese population. The obtained results were comparable to those of gene frequencies in previous Xia’s study in Guangzhou Chinese population but significant difference from earliest reported European frequencies, confirming geographical difference exist. [3-5] However, due to small sample size in this study, further examination in larger sample may allow more representative frequencies for the Hong Kong population.