Haptoglobin polymorphisms are associated with Crohn's disease, disease behavior, and extraintestinal manifestations in Hungarian patients

The failure of biological treatment in axial spondyloarthritis is linked to the factors related to increased intestinal permeability and dysbiosis: prospective observational cohort study

BACKGROUND

A significant number of patients with axial spondyloarthritis (axSpA) do not respond to biological therapy. Therefore, we decided to investigate the specificity of this group of patients and, in particular, whether haptoglobin (Hp), its polymorphism and zonulin, in addition to other clinical features, are predictors of poor response to biological treatment.

METHODS

48 patients with axSpA who were unsuccessfully treated with standard drugs were converted to biological treatment, and from this time on, a 12-week follow-up was started to assess the failure of biological treatment (Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) decrease < 2 points). Predictors of treatment failure were identified using logistic regression analysis.

RESULTS

21% of subjects had biological treatment failure. Patients who had a higher zonulin level, a history of frequent infections, were older, had inflammatory bowel disease (IBD), had a lower Hp level at the time of inclusion in biological therapy showed an increased risk of treatment failure.

CONCLUSIONS

The results of the study support the hypothesis that the effectiveness of biological treatment of axSpA is limited by changed microbiota and intestinal epithelial barrier dysfunction, as an increased risk of biological treatment failure was observed in patients who were older, had higher zonulin level, IBD and repeated courses of antibiotics due to frequent infections. Therefore, starting biological treatment should be followed by reducing intestinal permeability and regulating the disturbed gut microbiome.

Unlocking the link between haptoglobin polymorphism and noninfectious human diseases: insights and implications

Haptoglobin (Hp) is a polymorphic protein that was initially described as a hemoglobin (Hb)-binding protein. The major functions of Hp are to scavenge Hb, prevent iron loss, and prevent heme-based oxidation. Hp regulates angiogenesis, nitric oxide homeostasis, immune responses, and prostaglandin synthesis. Genetic polymorphisms in the Hp gene give rise to different phenotypes, including Hp 1-1, Hp 2-1, and Hp 2-2. Extensive research has been conducted to investigate the association between Hp polymorphisms and several medical conditions including cardiovascular disease, inflammatory bowel disease, cancer, transplantation, and hemoglobinopathies. Generally, the Hp 2-2 phenotype is associated with increased disease risk and poor outcomes. Over the years, the Hp 2 allele has spread under genetic pressures. Individuals with the Hp 2-2 phenotype generally exhibit lower levels of CD163 expression in macrophages. The decreased expression of CD163 may be associated with the poor antioxidant capacity in the serum of subjects carrying the Hp 2-2 phenotype. However, the Hp 1-1 phenotype may confer protection in some cases. The Hp1 allele has strong antioxidant, anti-inflammatory, and immunomodulatory properties. It is important to note that the benefits of the Hp1 allele may vary depending on genetic and environmental factors as well as the specific disease or condition under consideration. Therefore, the Hp1 allele may not necessarily confer advantages in all situations, and its effects may be context-dependent. This review highlights the current understanding of the role of Hp polymorphisms in cardiovascular disease, inflammatory bowel disease, cancer, transplantation, hemoglobinopathies, and polyuria.

Genome-Wide Association Analysis of Protein-Coding Variants in IgA Nephropathy

SIGNIFICANCE STATEMENT

Genome-wide association studies have identified nearly 20 IgA nephropathy susceptibility loci. However, most nonsynonymous coding variants, particularly ones that occur rarely or at a low frequency, have not been well investigated. The authors performed a chip-based association study of IgA nephropathy in 8529 patients with the disorder and 23,224 controls. They identified a rare variant in the gene encoding vascular endothelial growth factor A (VEGFA) that was significantly associated with a two-fold increased risk of IgA nephropathy, which was further confirmed by sequencing analysis. They also identified a novel common variant in PKD1L3 that was significantly associated with lower haptoglobin protein levels. This study, which was well-powered to detect low-frequency variants with moderate to large effect sizes, helps expand our understanding of the genetic basis of IgA nephropathy susceptibility.

BACKGROUND

Genome-wide association studies have identified nearly 20 susceptibility loci for IgA nephropathy. However, most nonsynonymous coding variants, particularly those occurring rarely or at a low frequency, have not been well investigated.

METHODS

We performed a three-stage exome chip-based association study of coding variants in 8529 patients with IgA nephropathy and 23,224 controls, all of Han Chinese ancestry. Sequencing analysis was conducted to investigate rare coding variants that were not covered by the exome chip. We used molecular dynamic simulation to characterize the effects of mutations of VEGFA on the protein's structure and function. We also explored the relationship between the identified variants and the risk of disease progression.

RESULTS

We discovered a novel rare nonsynonymous risk variant in VEGFA (odds ratio, 1.97; 95% confidence interval [95% CI], 1.61 to 2.41; P = 3.61×10 -11 ). Further sequencing of VEGFA revealed twice as many carriers of other rare variants in 2148 cases compared with 2732 controls. We also identified a common nonsynonymous risk variant in PKD1L3 (odds ratio, 1.16; 95% CI, 1.11 to 1.21; P = 1.43×10 -11 ), which was associated with lower haptoglobin protein levels. The rare VEGFA mutation could cause a conformational change and increase the binding affinity of VEGFA to its receptors. Furthermore, this variant was associated with the increased risk of kidney disease progression in IgA nephropathy (hazard ratio, 2.99; 95% CI, 1.09 to 8.21; P = 0.03).

CONCLUSIONS

Our study identified two novel risk variants for IgA nephropathy in VEGFA and PKD1L3 and helps expand our understanding of the genetic basis of IgA nephropathy susceptibility.

Targeted genotyping for the prediction of celiac disease autoimmunity development in patients with type 1 diabetes and their family members

BACKGROUND

Patients with type 1 diabetes (T1D) and their first-degree relatives (FDRs) have an increased risk of developing celiac disease (CD) compared to the general population. This is largely explained by the shared association with major histocompatibility class II human leukocyte antigen (HLA) DQ2 and/or DQ8 between the two disease states.

AIM

To describe the frequency of CD autoimmunity (CDA) and the distribution of HLA and haptoglobin genotypes in patients with T1D and their FDRs. Additionally, we aimed at identifying predictors associated with an increased risk of developing CDA in patients with T1D and their family members.

METHODS

We obtained clinical information and blood samples from 1027 participants (302 with T1D and 725 FDRs) over a five-year period. Samples were tested for autoantibodies associated with CD, HLA-DQ alleles, and haptoglobin genotype. We fit univariate and multiple logistic regression models for CDA separately for subjects with T1D and for FDRs of subjects with T1D.

RESULTS

Implementation of a screening program increased the frequency of CDA by 2-fold in participants with T1D and 2.8-fold in their FDRs. Multivariate analysis found that, in participants with T1D, having both DR7-DQ2 and DR4-DQ8 was associated with an increased frequency of CDA. In FDRs of T1D patients, reported CD in the family was associated with an increased frequency of CDA during screening. Haptoglobin 2 genotype was not associated with developing CDA in the multivariate analysis.

CONCLUSION

Patients with T1D and their FDRs have a high frequency of CDA. Carrying both DR7-DQ2 and DR4-DQ8 was associated with development of CDA in patients with T1D.

Haptoglobin

Haptoglobin (Hp) is an abundant human plasma protein that tightly captures hemoglobin (Hb) during hemolysis. The Hb-Hp complex formation reduces the oxidative properties of heme/Hb and promotes recognition by the macrophage scavenger receptor CD163. This leads to Hb-Hp breakdown and heme catabolism by heme oxygenase and biliverdin reductase. Gene duplications of a part of or the entire Hp gene in the primate evolution have led to variant Hp gene products that collectively may be designated "the haptoglobins (Hps)" as they all bind Hb. These variant products include the human-specific multimeric Hp phenotypes in individuals, which are hetero- or homozygous for an Hp² gene allele. The Hp-related protein (Hpr) is another Hp duplication product in humans and other primates. Alternative functions of the variant Hps are indicated by numerous reports on association between Hp phenotypes and disease as well as the elucidation of a specific role of Hpr in the innate immune defense. Recent Advances: Recent functional and structural information on Hp and receptor systems for Hb removal now provides insight on how Hp carries out essential functions such as the Hb detoxification/removal, and how Hpr, by acting as an Hp-lookalike, can sneak a lethal toxin into trypanosome parasites that cause mammalian sleeping sickness. Critical Issues and Future Directions: The new structural insight may facilitate ongoing attempts of developing Hp derivatives for prevention of Hb toxicity in hemolytic diseases such as sickle cell disease and other hemoglobinopathies. Furthermore, the new structural knowledge may help identifying yet unknown functions based on other disease-relevant biological interactions involving Hps. Antioxid. Redox Signal. 26, 814-831.

Zonulin transgenic mice show altered gut permeability and increased morbidity/mortality in the DSS colitis model

Increased small intestinal permeability (IP) has been proposed to be an integral element, along with genetic makeup and environmental triggers, in the pathogenies of chronic inflammatory diseases (CIDs). We identified zonulin as a master regular of intercellular tight junctions linked to the development of several CIDs. We aim to study the role of zonulin-mediated IP in the pathogenesis of CIDs. Zonulin transgenic Hp2 mice (Ztm) were subjected to dextran sodium sulfate (DSS) treatment for 7 days, followed by 4-7 days' recovery and compared to C57Bl/6 (wild-type (WT)) mice. IP was measured in vivo and ex vivo, and weight, histology, and survival were monitored. To mechanistically link zonulin-dependent impairment of small intestinal barrier function with clinical outcome, Ztm were treated with the zonulin inhibitor AT1001 added to drinking water in addition to DSS. We observed increased morbidity (more pronounced weight loss and colitis) and mortality (40-70% compared with 0% in WT) at 11 days post-DSS treatment in Ztm compared with WT mice. Both in vivo and ex vivo measurements showed an increased IP at baseline in Ztm compared to WT mice, which was exacerbated by DSS treatment and was associated with upregulation of zonulin gene expression (fourfold in the duodenum, sixfold in the jejunum). Treatment with AT1001 prevented the DSS-induced increased IP both in vivo and ex vivo without changing zonulin gene expression and completely reverted morbidity and mortality in Ztm. Our data show that zonulin-dependent small intestinal barrier impairment is an early step leading to the break of tolerance with subsequent development of CIDs.

Zonulin, a regulator of epithelial and endothelial barrier functions, and its involvement in chronic inflammatory diseases

Beside digesting nutrients and absorbing solutes and electrolytes, the intestinal epithelium with its barrier function is in charge of a tightly controlled antigen trafficking from the intestinal lumen to the submucosa. This trafficking dictates the delicate balance between tolerance and immune response causing inflammation. Loss of barrier function secondary to upregulation of zonulin, the only known physiological modulator of intercellular tight junctions, leads to uncontrolled influx of dietary and microbial antigens. Additional insights on zonulin mechanism of action and the recent appreciation of the role that altered intestinal permeability can play in the development and progression of chronic inflammatory disorders has increased interest of both basic scientists and clinicians on the potential role of zonulin in the pathogenesis of these diseases. This review focuses on the recent research implicating zonulin as a master regulator of intestinal permeability linked to the development of several chronic inflammatory disorders.

Comorbidity between depression and inflammatory bowel disease explained by immune-inflammatory, oxidative, and nitrosative stress; tryptophan catabolite; and gut-brain pathways

The nature of depression has recently been reconceptualized, being conceived as the clinical expression of activated immune-inflammatory, oxidative, and nitrosative stress (IO&NS) pathways, including tryptophan catabolite (TRYCAT), autoimmune, and gut-brain pathways. IO&NS pathways are similarly integral to the pathogenesis of inflammatory bowel disease (IBD). The increased depression prevalence in IBD associates with a lower quality of life and increased morbidity in IBD, highlighting the role of depression in modulating the pathophysiology of IBD.This review covers data within such a wider conceptualization that better explains the heightened co-occurrence of IBD and depression. Common IO&NS underpinning between both disorders is evidenced by increased pro-inflammatory cytokine levels, eg, interleukin-1 (IL-1) and tumor necrosis factor-α, IL-6 trans-signalling; Th-1- and Th-17-like responses; neopterin and soluble IL-2 receptor levels; positive acute phase reactants (haptoglobin and C-reactive protein); lowered levels of negative acute phase reactants (albumin, transferrin, zinc) and anti-inflammatory cytokines (IL-10 and transforming growth factor-β); increased O&NS with damage to lipids, proteinsm and DNA; increased production of nitric oxide (NO) and inducible NO synthase; lowered plasma tryptophan but increased TRYCAT levels; autoimmune responses; and increased bacterial translocation. As such, heightened IO&NS processes in depression overlap with the biological underpinnings of IBD, potentially explaining their increased co-occurrence. This supports the perspective that there is a spectrum of IO&NS disorders that includes depression, both as an emergent comorbidity and as a contributor to IO&NS processes. Such a frame of reference has treatment implications for IBD when "comorbid" with depression.

Detecting non-allelic homologous recombination from high-throughput sequencing data

Non-allelic homologous recombination (NAHR) is a common mechanism for generating genome rearrangements and is implicated in numerous genetic disorders, but its detection in high-throughput sequencing data poses a serious challenge. We present a probabilistic model of NAHR and demonstrate its ability to find NAHR in low-coverage sequencing data from 44 individuals. We identify NAHR-mediated deletions or duplications in 109 of 324 potential NAHR loci in at least one of the individuals. These calls segregate by ancestry, are more common in closely spaced repeats, often result in duplicated genes or pseudogenes, and affect highly studied genes such as GBA and CYP2E1.

The role of Haptoglobin and its related protein, Zonulin, in inflammatory bowel disease

Crohn's disease (CD) and ulcerative colitis (UC), collectively called inflammatory bowel disease (IBD), are immune-mediated conditions characterized by a chronic inflammation of the gut. Their precise etiology is unknown, although an increased intestinal permeability has been shown to play a central role in the pathogenesis of IBD. The intestinal epithelium provides the largest interface between the external environment and the host, and is thus a crucial regulation site of innate and adaptive immunity. Zonulin is one of the few known physiological mediators of paracellular intestinal permeability. It was found upregulated in different immune diseases like Celiac disease and Type 1 Diabetes (T1D). Recently, human zonulin was identified as prehaptoglobin-2 (pre-HP2) which before only had been regarded as the inactive precursor for HP2. Haptoglobin (HP) is a hemoglobin-binding protein with immunomodulatory properties. Its gene harbors a common polymorphism with 2 different alleles: HP1 and HP2. Allele HP2 and genotype HP22 has been shown to be overrepresented in different immune diseases like Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE) and T1D, and has also been found to be more frequent in patients with IBD (UC and CD) than in healthy controls.   In order to get some clues about the mechanism of action of HP(2) in IBD pathogenesis, we here review the current state of knowledge about zonulin and haptoglobin structure and function, and their plausible role in immune mediated diseases with an emphasis on IBD.

Thrombospondin-1 type 1 repeats in a model of inflammatory bowel disease: transcript profile and therapeutic effects

Thrombospondin-1 (TSP-1) is a matricellular protein with regulatory functions in inflammation and cancer. The type 1 repeats (TSR) domains of TSP-1 have been shown to interact with a wide range of proteins that result in the anti-angiogenic and anti-tumor properties of TSP-1. To ascertain possible functions and evaluate potential therapeutic effects of TSRs in inflammatory bowel disease, we conducted clinical, histological and microarray analyses on a mouse model of induced colitis. We used dextran sulfate sodium (DSS) to induce colitis in wild-type (WT) mice for 7 days. Simultaneously, mice were injected with either saline or one form of TSP-1 derived recombinant proteins, containing either (1) the three type 1 repeats of the TSP-1 (3TSR), (2) the second type 1 repeat (TSR2), or (3) TSR2 with the RFK sequence (TSR2+RFK). Total RNA isolated from the mice colons were processed and hybridized to mouse arrays. Array data were validated by real-time qPCR and immunohistochemistry. Histological and disease indices reveal that the mice treated with the TSRs show different patterns of leukocytic infiltration and that 3TSR treatment was the most effective in decreasing inflammation in DSS-induced colitis. Transcriptional profiling revealed differentially expressed (DE) genes, with the 3TSR-treated mice showing the least deviation from the WT-water controls. In conclusion, this study shows that 3TSR treatment is effective in attenuating the inflammatory response to DSS injury. In addition, the transcriptomics work unveils novel genetic data that suggest beneficial application of the TSR domains in inflammatory bowel disease.

Association of peroxisome proliferator-activated receptor gamma polymorphisms with inflammatory bowel disease in a Hungarian cohort

BACKGROUND

Inflammatory bowel disease (IBD) shows increasing incidence in the last few years in Eastern Europe, including Hungary. Since genetic susceptibility of patients plays an important role in the development and pathogenesis of IBD, it is important to identify new susceptibility genes. Peroxisome proliferator-activated receptor gamma (PPARγ) is expressed in the colon and has protective effects against inflammatory processes. Our aim was to examine the association of four polymorphisms of PPARγ in a well-characterized Hungarian IBD cohort.

METHODS

In all, 575 Crohn's disease (CD), 103 ulcerative colitis (UC) patients, and 486 sex- and age-matched controls were examined. Four polymorphisms of PPARγ (rs10865710 [C-681G], rs2067819, rs3892175, and rs1801282 [Pro12Ala]) were genotyped by TaqMan genotyping assays.

RESULTS

The Pro12Ala polymorphism showed significant association with CD when the frequencies of the homozygous variants (Pro/Pro vs. Ala/Ala) were compared. The minor Ala/Ala genotype was significantly less frequent in CD patients compared to the controls (odds ratio [OR] = 0.33; 95% confidence interval [CI] = 012-0.94; P = 0.03), suggesting a potential protective effect of the Ala allele. The GAGG haplotype of PPARγ confers a protective effect in CD; however, it is not significant, but in UC it has a protective effect with a significant level (OR = 0.14; 95% CI: 0.05-0.42; P = 3.78 × 10(-5) ), while GAGC increases the risk of UC (OR = 6.70; 95% CI: 3.41-13.17; P = 3.85 × 10(-10) ).

CONCLUSIONS

In the present study we demonstrated a significant association between PPARγ polymorphisms and the development of CD and UC at single loci level and also in haplotype combinations.

Gene expression changes associated with resistance to intravenous corticosteroid therapy in children with severe ulcerative colitis

BACKGROUND AND AIMS

Microarray analysis of RNA expression allows gross examination of pathways operative in inflammation. We aimed to determine whether genes expressed in whole blood early following initiation of intravenous corticosteroid treatment can be associated with response.

METHODS

From a prospectively accrued cohort of 128 pediatric patients hospitalized for intravenous corticosteroid treatment of severe UC, we selected for analysis 20 corticosteroid responsive (hospital discharge or PUCAI ≤45 by day 5) and 20 corticosteroid resistant patients (need for second line medical therapy or colectomy, or PUCAI >45 by day 5). Total RNA was extracted from blood samples collected on day 3 of intravenous corticosteroid therapy. The eluted transcriptomes were quantified on Affymetrix Human Gene 1.0 ST arrays. The data was analysed by the local-pooled error method for discovery of differential gene expression and false discovery rate correction was applied to adjust for multiple comparisons.

RESULTS

A total of 41 genes differentially expressed between responders and non-responders were detected with statistical significance. Two of these genes, CEACAM1 and MMP8, possibly inhibited by methylprednisolone through IL8, were both found to be over-expressed in non-responsive patients. ABCC4 (MRP4) as a member of the multi-drug resistance superfamily was a novel candidate gene for corticosteroid resistance. The expression pattern of a cluster of 10 genes selected from the 41 significant hits were able to classify the patients with 80% sensitivity and 80% specificity.

CONCLUSIONS

Elevated expression of several genes involved in inflammatory pathways was associated with resistance to intravenous corticosteroid therapy early in the course of treatment. Gene expression profiles may be useful to classify resistance to intravenous corticosteroids in children with severe UC and assist with clinical management decisions.

Possible pathogenetic role of vascular, immunological and genetic factors in certain gastoenterological disorders

A coeliakia és a gyulladásos bélbetegségek (IBD) változatos klinikai megjelenését befolyásoló faktorok jelentős része ismeretlen. A haptoglobin (Hp) molekula három fő fenotípusa eltérő antioxidáns, scavenger és immunmoduláns tulajdonsággal rendelkezik. Nagyszámú coeliakiás és IBD-betegben vizsgáltuk a Hp-polimorfizmus megoszlását és a betegség klinikai megjelenésével való lehetséges kapcsolatát. A Hp-fenotípusokat szérumból nátrium-dodecil-szulfát poliakrilamid gélelektroforézis (SDS-PAGE) és immunblottal határoztuk meg, amely egyértelműen azonosítja a genotípust is. Coeliakiában a kontrollpopulációhoz képest a Hp 2-1 fenotípus előfordulása szignifikánsan gyakoribb volt, míg a Hp 2-2 ritkább. A Hp 2-2 esetén azonban a súlyos, malabszorpcióval jelentkező klinikai betegség kockázata magasabb volt, míg a silent betegségé jóval alacsonyabb. Crohn-betegekben (CD) a Hp 2-1 fenotípus esetén a gyulladásos betegségforma előfordulása szignifikánsan gyakoribb volt a másik két Hp-fenotípushoz viszonyítva, míg a stenotizáló formáé ritkább. Primer szklerotizáló cholangitisben a Hp 1-1 fenotípus nem fordult elő. A Hp szerepét az immunreakciókban betöltött modulálóhatásai és eltérő térszerkezete magyarázhatja. A mikrobiális és autoantigének elleni szerológiai válasz segítséget jelenthet az IBD differenciáldiagnosztikájában, és összefüggést mutat a betegség fenotípusával. Nagyszámú IBD-betegben vizsgáltuk az anti- Saccharomyces cerevisiae (ASCA) és külső membránporin elleni antitestek (anti-Omp) enzimmel kapcsolt immunoszorbens assay (ELISA), illetőleg az atípusos perinukleáris antineutrophil citoplazmatikus antitest (P-ANCA) (indirekt immunfluoreszcencia) előfordulási gyakoriságát és a betegség fenotípusával való lehetséges kapcsolatukat. A szerológiai markerek hasznosnak bizonyultak az IBD differenciáldiagnosztikájában. CD-ben az ASCA- és az anti-Omp-pozitivitás a vékonybél-érintettség és a nem gyulladásos betegségforma szempontjából logisztikus regressziós analízisben is független rizikófaktornak bizonyult, míg a műtéti kockázat tekintetében nem. A nem gyulladásos típusú vékonybél-CD és az antimikrobiális antitest pozitivitásainak száma, illetőleg az antitesttiterek között szintén pozitív korrelációt találtunk (szerológiai-dózis hatás). Továbbá ASCA és az anti-Omp-antitestek jelenléte kapcsolatot mutatott a nucleotid oligomerizációs domén (NOD2/CARD15) genotípussal, és előfordulási gyakoriságuk szignifikánsan nőtt a NOD2/CARD15 mutációk számának növekedésével, ami gén-dózis hatásra utal és alátámasztja a mikrobákkal szembeni megváltozott érzékelés szerepét a CD patogenezisében.

The association of Haptoglobin polymorphism with Crohn's disease in Israel

OBJECTIVES

Haptoglobin is a α(2)-sialoglycoprotein with hemoglobin binding capacity. Functional differences between the Hp phenotypes with the Hp 1-1 protein being a superior anti-inflammatory to the Hp 2-2 protein have been identified. The aim of our study was to investigate the possible role of Hp polymorphism in the susceptibility to Crohn's disease and its clinical course.

METHODS

Hp phenotypes were determined for 382 Israeli CD patients and 3243 healthy controls. Phenotypic data for all Crohn's disease patients were carefully characterized. Analysis was preformed to evaluate the association between Hp polymorphism and Crohn's disease.

RESULTS

The frequency of Haptoglobin 1-1 was lower in Crohn's disease patients than in healthy individuals (6.28% vs. 9.28%, P=0.057). There was no association between Haptoglobin phenotypes and disease location, behavior or extra-intestinal manifestations. No association was found between the Haptoglobin polymorphism and the frequency of the three Crohn's disease associated NOD2 mutations examined.

CONCLUSIONS

We found a borderline significant decrease of the Haptoglobin 1-1 phenotype in Israeli Crohn's disease patients compared to healthy controls. Our findings may support the importance of inflammation in Crohn's disease pathogenesis and the protective function of Haptoglobin 1-1 in the susceptibility for Crohn's disease.

Haptoglobin, inflammation and disease

Haptoglobin is an acute phase protein that scavenges haemoglobin in the event of intravascular or extravascular haemolysis. The protein exists in humans as three main phenotypes, Hp1-1, Hp2-2 and Hp2-1. Accumulated data on the protein's function has established its strong association with diseases that have inflammatory causes. These include parasitic (malaria), infectious (HIV, tuberculosis) and non-infectious diseases (diabetes, cardiovascular disease and obesity) among others. Phenotype-dependent poor disease outcomes have been linked with the Hp2-2 phenotype. The present review brings this association into perspective by looking at the functions of the protein and how defects in these functions associated with the Hp2 allele affect disease outcome. A model is provided to explain the mechanism, which appears to be largely immunomodulatory.

Haptoglobin polymorphism: a novel genetic risk factor for celiac disease development and its clinical manifestations

BACKGROUND

Haptoglobin (Hp) alpha-chain alleles 1 and 2 account for 3 phenotypes that may influence the course of inflammatory diseases via biologically important differences in their antioxidant, scavenging, and immunomodulatory properties. Hp1-1 genotype results in the production of small dimeric, Hp2-1 linear, and Hp2-2 cyclic polymeric haptoglobin molecules. We investigated the haptoglobin polymorphism in patients with celiac disease and its possible association to the presenting symptoms.

METHODS

We studied 712 unrelated, biopsy-proven Hungarian celiac patients (357 children, 355 adults; severe malabsorption 32.9%, minor gastrointestinal symptoms 22.8%, iron deficiency anemia 9.4%, dermatitis herpetiformis 15.6%, silent disease 7.2%, other 12.1%) and 384 healthy subjects. We determined haptoglobin phenotypes by gel electrophoresis and assigned corresponding genotypes.

RESULTS

Hp2-1 was associated with a significant risk for celiac disease (P = 0.0006, odds ratio [OR] 1.54, 95% CI 1.20-1.98; prevalence 56.9% in patients vs 46.1% in controls). It was also overrepresented among patients with mild symptoms (69.2%) or silent disease (72.5%). Hp2-2 was less frequent in patients than in controls (P = 0.0023), but patients having this phenotype were at an increased risk for severe malabsorption (OR 2.21, 95% CI 1.60-3.07) and accounted for 45.3% of all malabsorption cases. Celiac and dermatitis herpetiformis patients showed similar haptoglobin phenotype distributions.

CONCLUSIONS

The haptoglobin polymorphism is associated with susceptibility to celiac disease and its clinical presentations. The predominant genotype in the celiac population was Hp2-1, but Hp2-2 predisposed to a more severe clinical course. The phenotype-dependent effect of haptoglobin may result from the molecule's structural and functional properties.