Exome-chip meta-analysis identifies association between variation in <i>ANKRD26</i> and platelet aggregation

Previous genome-wide association studies (GWAS) have identified several variants associated with platelet function phenotypes; however, the proportion of variance explained by the identified variants is mostly small. Rare coding variants, particularly those with high potential for impact on protein structure/function, may have substantial impact on phenotype but are difficult to detect by GWAS. The main purpose of this study was to identify low frequency or rare variants associated with platelet function using genotype data from the Illumina HumanExome Bead Chip. Three family-based cohorts of European ancestry, including ~4,000 total subjects, comprised the discovery cohort and two independent cohorts, one of European and one of African American ancestry, were used for replication. Optical aggregometry in platelet-rich plasma was performed in all the discovery cohorts in response to adenosine diphosphate (ADP), epinephrine, and collagen. Meta-analyses were performed using both gene-based and single nucleotide variant association methods. The gene-based meta-analysis identified a significant association (P = 7.13 × 10^–7) between rare genetic variants in <i>ANKRD26</i> and ADP-induced platelet aggregation. One of the <i>ANKRD26</i> SNVs - rs191015656, encoding a threonine to isoleucine substitution predicted to alter protein structure/function, was replicated in Europeans. Aggregation increases of ~20–50% were observed in heterozygotes in all cohorts. Novel genetic signals in <i>ABCG1</i> and <i>HCP5</i> were also associated with platelet aggregation to ADP in meta-analyses, although only results for <i>HCP5</i> could be replicated. The SNV in <i>HCP5</i> intersects epigenetic signatures in CD41+ megakaryocytes suggesting a new functional role in platelet biology for HCP5. This is the first study to use gene-based association methods from SNV array genotypes to identify rare variants related to platelet function. The molecular mechanisms and pathophysiological relevance for the identified genetic associations requires further study.既往全基因组关联研究（Genome-Wide Association Study, GWAS）已鉴定出多个与血小板功能表型相关的遗传变异，但已鉴定变异所解释的表型方差占比普遍较低。罕见编码变异，尤其是那些对蛋白质结构/功能具有较高潜在影响的变异，可能对表型产生显著作用，但难以通过GWAS检测到。本研究的主要目的是利用Illumina人类外显子组芯片（Illumina HumanExome Bead Chip）的基因型数据，鉴定与血小板功能相关的低频或罕见变异。本研究纳入3个欧洲血统的家系队列（总样本量约4000例）作为发现队列，同时使用2个独立队列进行验证——分别为欧洲血统队列与非裔美国人血统队列。所有发现队列均针对二磷酸腺苷（adenosine diphosphate, ADP）、肾上腺素及胶原刺激，开展了富血小板血浆的光学聚集试验。研究同时采用基于基因的关联分析与单核苷酸变异（single nucleotide variant, SNV）关联分析方法进行荟萃分析。基于基因的荟萃分析鉴定出ANKRD26基因内的罕见遗传变异与ADP诱导的血小板聚集存在显著关联（P=7.13×10^–7）。其中一个ANKRD26基因的SNV——rs191015656，其编码的苏氨酸突变为异亮氨酸，被预测可改变蛋白质结构/功能，该变异在欧洲血统队列中得到验证。在所有队列的杂合子个体中均观察到约20%~50%的聚集反应增强。荟萃分析还发现ABCG1与HCP5基因内的新型遗传信号同样与ADP诱导的血小板聚集相关，但仅HCP5的结果得到了验证。HCP5基因内的SNV与CD41+巨核细胞的表观遗传特征存在重叠，提示HCP5在血小板生物学中存在新的功能作用。本研究是首个利用基于SNV芯片的基因型数据、通过基因关联分析方法鉴定血小板功能相关罕见变异的研究。上述已鉴定的遗传关联的分子机制及病理生理相关性仍需进一步研究。