Genetic factors associated with serum haptoglobin level in a Japanese population
Introduction
Haptoglobin (HP) is an acute-phase protein synthesized mainly in the liver; it binds free hemoglobin released by hemolysis or normal red blood cell turnover, thus preventing oxidative damage [1]. The three major subtypes, HP1-1, HP2-1, and HP2-2, are products of two co-dominant alleles, HP1 and HP2, encoded by the HP gene, which is located on chromosome 16. The frequency of the “common alleles” varies among worldwide populations with HP1 frequencies from 0.07 in parts of India to over 0.7 in parts of West Africa and South America [1]. Many diseases have been reported to be associated with the major HP subtypes. Such associations may be due to functional differences between HP1 and HP2 in the binding of hemoglobin and its rate of clearance from serum [1].
The serum level of HP reflects various clinical states such as infectious diseases, malignancy, autoimmune disease, and tissue necrosis. It increases by 200–500% during the seven days after the onset of inflammation [2]. On the other hand, levels decrease during hemolysis, ineffective erythropoiesis, liver disease, and late pregnancy [1], [3]. Recently, measurement of the HP level as one of the inflammatory variables has been shown to improve the prediction of major cardiovascular events [4].
On the other hand, inter-individual variability of the circulating HP level also exists. Gender, age, smoking, and plasma hemoglobin levels were shown to be associated with the HP concentrations in human plasma [5]. In addition, some genetic factors have been reported to affect the HP serum level. Serum HP concentrations are dependent on the major HP subtypes (HP1-1, HP2-1, HP2-2), although they seem to differ among different populations [1]. We previously identified a haptoglobin gene deletion (HPdel) as a causal mutation of anhaptoglobinemia in a Japanese population and inferred the possibility that the allele may be responsible for hypohaptoglobinemia in the heterozygous state, although the sample size was small [6]. The HPdel, which lacks an approximately 28-kb segment that extends from the promoter region to exon 5 of the haptoglobin-related gene, is distributed only in East and Southeast Asian populations with a frequency of 0.009–0.38 [3], [6], [7], [8]. More recently, a genome-wide association study (GWAS) of European children identified one SNP, rs2000999, as a strong genetic determinant of the serum HP level [5], [9]. In a public database (http://www.ncbi.nlm.nih.gov/projects/SNP), this SNP is distributed unequally throughout the global population with a minor allele frequency (MAF) of 0.047–0.476.
Promoter SNPs have also been reported to be associated with HP expression. A SNP at position − 61 (rs5471) was identified as causal polymorphism of HP 2-1 modified phenotypes due to a decreased amount of HP2 polypeptide relative to that of HP1 [10]. The distribution of rs5471 seems to be restricted to Africans and Hispanics (http://www.ncbi.nlm.nih.gov/projects/SNP/) [11]. Recently, HP was identified as one of the genes upregulated in peripheral blood mononuclear cells (PBMCs) of the short-term survival group of advanced castration-resistant prostate cancer (CRPC) patients after cancer peptide vaccination [12]. In addition, a significant correlation between promoter polymorphism at position − 55 (rs5472), and CRPC prognosis or HP expression level was observed in PBMCs before vaccination (personal communication). The MAF of rs5472 seems to be relatively high in many populations (http://www.ncbi.nlm.nih.gov/projects/SNP/) [11]. The gene structures of HP1, HP2, and HPdel and the relative positions of rs5472 and rs2000999 are indicated in Fig. 1.
In this study, we have not only reconfirmed previous findings that common alleles, HPdel and SNP rs2000999 were partly responsible for inter-individual variability of HP, but also found SNP rs5472 located in the promoter region of the HP gene to affect the serum HP level. In addition, we demonstrated the impact of each of the polymorphisms and also observed a direct relationship among the polymorphisms by using the hemizygotes of the HP gene and its flanking sequence.
Section snippets
Materials and methods
This study protocol was approved by the ethics committee of Kurume University School of Medicine.
Association between serum HP level and genetic polymorphisms
We analyzed the association between each of polymorphisms and serum HP level in 194 HPdel heterozygotes and 385 randomly selected samples without HPdel out of 5679 Japanese samples.
First, the samples were divided into two groups according to the presence or absence of HPdel. As shown in Table 1, the median of HP/HPdel was only a quarter of that of HP/HP and the difference between the medians of the two groups was statistically significant. Then we doubled each HP/HPdel value and compared it
Discussion
In this study, all four polymorphisms studied seemed to be associated with serum HP concentration in a Japanese population. However, our samples had no information on potential confounder factors such as age, sex, BMI, biochemical values, or clinical status They are supposed to be considered in conducting association study as in the previous studies [5], [9]. This is the limitation of this study.
A previous analysis of HP2-1 modified phenotypes, which show low HP2 expression, suggested that a
Acknowledgments
We thank Ms. Katherine Ono for the English editing of this manuscript.
References (23)
- et al.
Inflammatory markers, lipoprotein components and risk of major cardiovascular events in 65,005 men and women in the Apolipoprotein MOrtality RISk study (AMORIS)
Atherosclerosis
(2010) - et al.
Clinical necessity of partitioning of human plasma haptoglobin reference intervals by recently-discovered rs2000999
Clin Chim Acta
(2012) - et al.
The haptoglobin-gene deletion responsible for anhaptoglobinemia
Am J Hum Genet
(1998) - et al.
A new statistical method for haplotype reconstruction from population data
Am J Hum Genet
(2001) - et al.
Haptoglobin polymorphism in Mongolian population: comparison of the two genotyping methods
Clin Chim Acta
(2009) - et al.
Simple PCR detection of haptoglobin gene deletion in anhaptoglobinemic patients with antihaptoglobin antibody that causes anaphylactic transfusion reactions
Blood
(2000) - et al.
Serum vitamin C concentration is influenced by haptoglobin polymorphism and iron status in Chinese
Clin Chim Acta
(2006) - et al.
Haptoglobin: a review of the major allele frequencies worldwide and their association with diseases
Int J Lab Hematol
(2007) - et al.
Acute-phase proteins and other systemic responses to inflammation
N Engl J Med
(1999) - et al.
Haplotype association between haptoglobin (Hp2) and Hp promoter SNP (A-61C) may explain previous controversy of haptoglobin and malaria protection
PLoS One
(2007)
The distribution of haptoglobin-gene deletion (Hpdel) is restricted to East Asians
Transfusion
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Serum haptoglobin correlates positively with cholesterol and triglyceride concentrations in an obese Mongolian population
2020, Clinica Chimica ActaCitation Excerpt :The zygosity of HPdel in addition to common HP alleles had been determined and reported [13]. Genotyping of rs2000999 (G > A polymorphism) was performed as described previously [22]. Our 927 subjects included 19 samples with rare alleles, i.e., 16 heterozygotes of HPdel and 3 heterozygotes of HP3.
Genetic determinants of circulating haptoglobin concentration
2019, Clinica Chimica ActaCitation Excerpt :Gender may affect circulating Hp level [18], so it was included as a covariate, but it did not have a significant relationship to Hp level in our analyses. Ancestry also impacts on circulating Hp level [13]. Some of the effect of ancestry could be due to inter-population differences in the frequencies of the HP CNV and rs2000999, but we show here that the effect of Asian/European status on Hp level persisted despite controlling for the HP CNV, rs2000999 and gender.
Association of the genetic variant rs2000999 with haptoglobin and diabetic macrovascular diseases in Chinese patients with type 2 diabetes
2019, Journal of Diabetes and its ComplicationsCitation Excerpt :According to this law, we performed an association analysis in patients without Hpdel. In the present study, the SNP rs2000999 was not in strong linkage disequilibrium with the common Hp CNV among Chinese T2DM patients, consistent with the data reported in the European and Japanese population.21,22 It was reported that rs2000999 A was in positive correlation with total cholesterol levels and LDL-C levels in individuals of European ancestry.6
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Current address: Department of Data Science, Kyoto University Hospital, Kyoto 606-8507, Japan.