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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 13  |  Issue : 1  |  Page : 38-43

Human leukocyte Antigen-B*27 allele subtype prevalence and disease association of ankylosing spondylitis among south indian population


1 Arthritis Superspeciality Center; Departments of Medicine, SDM College of Medical Sciences and Hospital, Hubli-Dharwad, Karnataka, India
2 Department of Biochemistry, SDM College of Medical Sciences and Hospital, Hubli-Dharwad, Karnataka, India
3 Jeevan Stem Cell Foundation, Chennai, Tamil Nadu, India
4 Arthritis Superspeciality Center, Hubli-Dharwad, Karnataka, India
5 Department of Physiology, SDM College of Medical Sciences and Hospital, Hubli-Dharwad, Karnataka, India

Date of Web Publication26-Feb-2018

Correspondence Address:
Dr. Praveenkumar Shetty
Department of Biochemistry, SDM College of Medical Sciences and Hospital, Hubali-Dharwad, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/injr.injr_95_17

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  Abstract 


Aim: Ankylosing spondylitis (AS) is a chronic inflammatory arthritis mainly affecting articular and extraarticular structures. AS clinical manifestations also involve sacroiliac joints and spine. Genetic factors play a key role in AS susceptibility. AS-associated subtypes of human leukocyte antigen (HLA)-B27 and other HLA-B alleles vary in different ethnic populations. There are no reports of HLA B genotype association to South Indian AS patients. In the current study, we have analyzed the HLA-B genotype association with 105 AS patients and 100 respective controls, we have also verified whether any specific clinical manifestation of AS has any pattern of HLA-B subtype association.
Methods: The patients with AS were diagnosed fulfilling ASAS criteria. Before enrolling the patients, the written informed consent was obtained. The peripheral blood DNA genotyping of HLA-B27 was performed in Applied Biotechnologies 3130/3500 sequencer using SeCore HLA B Class I typing high-resolution kit from Invitrogen.
Results: HLA B27 allele frequency in AS patients (74%) is significantly higher than healthy controls (3%). Most of the earlier studies associated AS with HLA B27 antigen. The current data illustrate that only 21% of AS patients presented HLA B27 antigen. HLA B27:05 and HLA B27:04 are the predominant subtypes. Early-onset of AS manifestations is seen in HLA B27 phenotypes than non-HLA B27 phenotypes. HLA B27 associated AS patients presented more severe axial manifestations such as bilateral sacroiliitis, erosions, and extra-articular features such as uveitis than non-HLA types. Positivity for HLA B27 allele predicts more severe disease course in South Indian patients with AS, similar to that in other populations.
Conclusion: The current study indicates that a majority of South Indian AS patients are associated with HLA-B*27 alleles. In addtion we found that HLA-B*27 associated AS patients presented with more severe axial manifestations.

Keywords: Ankylosing spondylitis, human leukocyte antigen-B*27, sacroilitis, spondyloarthropathy. arthritis


How to cite this article:
Haridas V, Shetty P, Kumar M N, Vasanthakumar K C, Haridas K, Khode V, Bargale A. Human leukocyte Antigen-B*27 allele subtype prevalence and disease association of ankylosing spondylitis among south indian population. Indian J Rheumatol 2018;13:38-43

How to cite this URL:
Haridas V, Shetty P, Kumar M N, Vasanthakumar K C, Haridas K, Khode V, Bargale A. Human leukocyte Antigen-B*27 allele subtype prevalence and disease association of ankylosing spondylitis among south indian population. Indian J Rheumatol [serial online] 2018 [cited 2019 Aug 17];13:38-43. Available from: http://www.indianjrheumatol.com/text.asp?2018/13/1/38/222120




  Introduction Top


Ankylosing spondylitis (AS) is a chronic inflammatory arthritis mainly affecting articular and extraarticular structures. AS is characterized by axial arthritis involving sacroiliac joints and spine, peripheral arthritis, enthesis with extra-articular features such as uveitis, inflammatory bowel disease, and psoriasis.[1] Recent studies have associated the risk of developing AS with multiple genetic and environmental factors.[2] Variations in several genes influence the risk of developing this disorder. Human leukocyte antigen (HLA)-B*27 is considered to be an important genetic marker associated with AS.[3],[4]

HLA-B27 is one of the HLA Class I molecules which are highly polymorphic and plays a major role in protective immunity against intracellular parasites including virus and bacteria.[5] HLA-B27 is a unique HLA Class I molecule, not only due to its high association with AS but also because it has characteristically different amino acid composition from other Class I molecules. There are two important characteristic structures which are different from others: the presence of B pocket and the free thiol group of Cys67.[6],[7]

According to the latest Immuno Polymorphism Database-ImMuno GeneTics/HLA (IPD-IMGT/HLA) database, there are about 161 subtypes of HLA B*27:01 to HLA B*27:161.[8] There is a variable distribution of HLA-B27 gene among world population, with the highest prevalence in northern territory of the earth. Eskimos and Native American in the circumpolar area and north Canada were known for their high carrier rate and some of the world's highest prevalence rates of spondyloarthropathies.[9],[10] HLA-B*27:05 is the most prevalent subtype and present in almost every population in the world,[11] associated to the extent of 90%–96%. It was thought that HLA-B*27:05 was the ancestor subtype, all other subtypes could have evolved from HLAB*27:05 by point mutation (B*27:03), reciprocal recombination (B*27:07, B*27:09) and gene conversion (B*27:01, B*27:02, B*27:04, B*27:06).[11],[12]

It is interesting to note that not all subtypes are associated with AS. In addition to B*27:05, most alleles such as B*27:01, B*27:02, B*27:03, B*27:04, B*27:10, B*27:13, B*27:14, B*27:15 are documented to be associated with AS.[13] In Caucasians AS is associated with HLA-B*2701, *2702, *2705, *2708, and *2709,[14] in Chinese, HLA-B*27:04 and in Mediterranean population it is HLA-B*27:02, whereas Asians have been associated with B*2704, *2706 and *2707. The subtype B*2706 is now known as B*2722 is a rare subtype identified only in some Southeast Asian populations and B*2709 in Sardinians are unrelated to the development of AS.[15],[16],[17] In African–Americans and West African populations, B*2703 is reported. HLA-B*27:02 is the predominant allele among the Middle East and Jewish populations.[18],[19],[20],[21] Even though there are few studies in India associating HLA-B antigen with population and clinical manifestations of AS,[22],[23] there are no reports of HLA-B genotype association to South Indian AS patients. In the current study, we have analyzed the HLA-genotype association with 105 AS patients and 100 respective controls. We have also verified whether any specific clinical manifestation of AS has any pattern of HLA-B subtype association.


  Methods Top


The patients with AS were diagnosed following ASAS criteria.[24] Age and gender-matched controls were selected randomly from healthy group; they were free of any history of rheumatic diseases. Consecutive AS patients were selected among those who have visited Rheumatology clinic during the study of 1 year. Rheumatologist evaluated all the patients and necessary radiographs, and clinical tests were performed to confirm the clinical status. The medical information related to patient history and disease status was collected. Patients with inflammatory low back pain for more than 3 months of duration with sacroiliitis on magnetic resonance imaging (MRI) were included in the study. Even though radiographic sacroiliitis was present, many of the patients had an MRI of the sacroiliac joint. Hence, all patients with MRI evidence of sacroilitis were included in the study. All the patients included were more than 16 years of age.

Peripheral blood was used to analyze the expression of HLA-B27 antigen on the T cell surface by flow cytometry assay using monoclonal antibody specific for HLA-B27. Human Genomic DNA was extracted from peripheral blood using QIAamp Blood DNA Mini QIA cube kit. The B locus-specific PCR amplification was performed using GeneAmp PCR System 9700. The targeted amplicon size was ~ 1400 bp. The amplicons were enzymatically purified by ExoSAP-IT. The exon (2, 3, and 4) specific cycle sequencing setup was performed using the SeCore Sequencing IVD kit by Invitrogen. The nucleotide chronology and resulting HLA subtype was determined by multicolor, fluorescence-based, Big Dye and results detected on an automated ABI 3730 × l DNA analyzer instrument. The sequencing data were analyzed using uTYPE 7.1 with reference to recent IPD-IMGT/HLA database.

Statistical analysis

Tests of association between genetic variants and AS were performed for each allele using SPSS version 20 (Chicago, USA). Exact P values were obtained (Fisher's exact test) from 2 × 2 tables of allele counts and disease status. The percentage of allele frequency presented will be almost double, when the prevalence of HLA B in patients is anticipated as two different alleles per patient excluding few homozygous cases.

Ethical approval

The study was approved by the ethics committee of the SDM College of Medical Sciences and Hospital. Informed written consent was obtained from all patients prior to their enrollment in this study.


  Results Top


In our study group of 105 patients with AS, males were more frequently affected than females (male:female ratio of 3.4:1). Duration of the disease at the time of diagnosis ranged from 1 year to 5 years. Out of 105 patients, only 22 showed positive for HLA and positive family history of AS was recorded in 25 patients (24%) [Table 1]. The predominant initial symptom was an inflammatory low back pain, sacroiliac joint involvement was observed in almost all patients with 92% demonstrating peripheral arthritis. Our HLA-B allele sequencing study revealed that both AS and controls together comprising of total 23 different alleles. Major common alleles identified in controls are B*35, B*40, and B*52 with corresponding allele frequency of 29%, 27%, and 24%, respectively as shown in the [Table 2]. The current study confirms the well-established association of AS with HLA-B*27 in South Indian population, occurring in the frequency of 74%. The non-HLA B*27 alleles such as B*07 (11%), B*15 (8%), B*35 (20%), B*40 (19%), B*51 (16%), and B*57 (9%) demonstrated almost same frequency in control as well as in AS patients. On the other hand, other carrier alleles such as B*58 (P< 0.182), B * 52 (P< 0.001), B*44 (P < 0.03), B*8 (P < 0.014), and B37 (P < 0.045) frequency was significantly lower in patients with AS compared to control population.
Table 1: Basic demographics of South Indian ankylosing spondylitis data

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Table 2: HLA-B allele frequency in South Indian ankylosing spondylitis patients and respective controls

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HLA-B*27 allele frequency in AS patients (74%) was significantly higher than healthy controls (3%). Current data illustrate that only 21% of AS patients presented HLA B*27 antigen positivity rather having 74% HLA-B*27 allele. This observation clarifies that even though HLA-B*27 phenotypes carry specific alleles, they may not be expressing the detectable quantity of antigens or the universally adapted flow cytometry screening method of detection of HLA antigen is not that specific. The data from the current population study [Table 3] demonstrated only four subtypes of HLA-B*27 (B*27:02, B*27:04, B*27:05 and B*27:07). Out of these, HLA-B*27:05 was most frequent (35% of the total patient pool) subtype followed by B*27:04 (23%) and further B*27:02 and B*27:07 were about 6% each. Control population showed the minimal presence of these genotypes as 1% each of B*27:04, B*27:05 and B*27:07. There were three cases of homozygous B*27 phenotypes noticed in the current AS study population without much altered clinical manifestations to the heterozygous group. In the current population study, HLA-B*40 allele association was found to be more in controls (23%) rather than in AS cases (16%). It is widely accepted that B27 antigen positive patients are likely to have active disease. In this respect, in the current study, we tried to correlate the different AS clinical manifestations with B*27 allele association. The age of AS onset in HLA-B*27 phenotype was early compared to non-HLA-B*27. In HLA-B*27 phenotypes, more patients were diagnosed in the 2nd decade (12–22 years, 28%) and in 3rd deacade (23–32 years, 42%). On the other hand, non-HLA-B*27 patients were diagnosed more in the latter period (after 33 years). All the patients included in the study had axial involvement [Table 4], HLA-B*27 associated AS patients predominantly demonstrated the severe axial manifestations such as bilateral sacroiliitis (84%, P < 0.0001) and erosion in the sacroiliac joint (76%, P < 0.001). As shown in [Table 5], non-HLA-B*27 phenotypes presented unilateral sacroiliitis (P < 0.05) with few erosion cases. Peripheral manifestations were not specific to HLA-B*27, even non-HLA-B*27 phenotypes demonstrated these manifestations. Very few cases of extra-articular manifestations were diagnosed, out of these few identified uveitis cases was predominantly present in HLA-B*27 phenotypes, followed by inflammatory bowel disease in two patients and psoriasis in four patients. All patients with inflammatory bowel disease and psoriasis were HLA-B*27 negative.
Table 3: HLA-B*27 subtype allele frequency in South Indian ankylosing spondylitis and control population

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Table 4: Diagnosis of ankylosing spondylitis according to axial, axial and peripheral and axial, peripheral and extra axial manifestations in study population

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Table 5: Association of severe axial manifestations of ankylosing spondylitis patients with HLA-B*27

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  Discussion Top


HLA-B*27 has the strongest genetic association with AS, which was established long ago.[25] HLA-B*27 was believed to have a role in antigen presentation, pathologic role in the development of AS and it has a tendency for the familial association.[4],[5],[7] The studies related to HLA-B*27 association with AS in Indian population is very few, and earlier research reported a broad range of frequency from 18% to 94%.[22],[23] B * 2705 (51%) and B*2704 (40%) are predominant in Northern India. In Western India, the main subtypes reported are B*2704, B*2705, and B*2707. Other alleles such as B*2702, B*2708, and B*2714 are also noticed in minor proportions.[26],[27],[28],[29],[30],[31] The current data indicate that HLA-B*27 association frequency with AS in South Indian population is 74%. Indian subcontinent populations have high genetic differentiation, and extensive substructuring and ancestry are unique to India due to evolutionary history, endogamy, and consanguinity.[32],[33],[34] This resulted in extensive MHC diversity to the Indian population.[35] Regarding HLA-B*27 subtypes, B*27:05 is widespread in all populations. The study also identified maximum B*27:05 and B*27:04 subtypes. Whereas B*27:03 is reported in Fula ethnic group,[36] B * 27:04 is the predominant subtype in South China population.[37] Most population studies around the world have reported the association of B*27:01, B*27:05, B*27:02, B*27:04, and B*27:07 with AS. B*27:01 and B*27:08 have not been identified in Indian population. *B27:08 is the Europian subtype.[19],[20],[21],[22],[23],[38] In contrast to the earlier reports, we did not find any B*27:13 and B*27:14 subtypes in our study population.[39] An earlier report associates HLA-B*40 allele with AS, but in our study, we could not find any significant association of this allele with AS.[40] The present study demonstrated no significant association between sex and specific subtypes of HLA-B*27. There is an unambiguous association of HLA-B*27 and family history of AS in the study population. Even though we did not find any significant association, but data clearly indicated that in non-HLA-B*27 phenotypes, manifestations of AS took place in the latter age group than HLA-B*27 associated AS patients, they presented the severe manifestations and diagnosed very early in the 2nd and 3rd decade of life. The late disease onset frequency was significantly higher in non-HLA B*27 AS patients as reported earlier.[41] With respect to various clinical manifestations, we could not associate different disease activity manifestations with HLA-B*27, but severe manifestations such as sacroiliac joint erosion, bilateral sacroiliitis were prevalent in HLA-B*27 phenotypes than non-HLA-B*27 AS patients. The current study confirmed the earlier report as uveitis was the most frequent extra-articular manifestation in AS and which was associated with HLA B*27, psoriasis and inflammatory bowel disease were presented in non-HLA B*27 phenotypes.[41],[42]

The B*27 alleles identified in this study, B*27:02, B*27:04, B*27:05 and B*27:07 are shared by Caucasians and Asians (North, West and East) but not by West Africans (B*27:03) and North Europians (B*27:08). The major alleles identified in our study B*27:05 and B*27:04 are observed in Eastern Siberian population, North America, North Europian, and South China descent. It is very difficult to resolve the evolutionary history of HLA subtype diversity in Indian population, as they show closer association with Indo–European speaking population of Central Asia.

Even though the current study is able to reflect the HLA B*27 allele picture in South Indian AS patients, It has a limitation of small sample size, further study with a higher number of patients is required to confirm the prevalence of HLA B*27 in general South Indian population.

The current study indicates that a majoirty of South Indian AS patients are associated with HLA-B*27 alleles and in that HLA-B*27:05 and HLA-B*27:04 are predominant subtypes. Early-onset of AS manifestations is seen in HLA-B*27 phenotypes than non-HLA-B*27 phenotypes. HLA-B*27 associated AS patients presented more severe axial manifestations like bilateral sacroiliitis and sacroiliac joint erosion and extra-articular uveitis than non-HLA types.

Acknowledgments

The authors would like to acknowledge the help rendered by Jeevan Stem cell foundation, Chennai, India, and Mr. Leonard Clinton D'souza for technical assistance.

Financial support and sponsorship

This work was supported by seed funding from Arthritis Super speciality center Hubli.

Conflicts of interest

There are no conflicts of interest.



 
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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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