HLA-B*27 subtyping by PCR-RFLP in Spanish patients with ankylosing spondylitis

High-Throughput and Automated Detection of HLA-B*27 Using the LabTurboTM AIO System

The adoption of an automated system can decrease the hands-on time requirements in a clinical laboratory setting. For the detection of HLA-B*27, implementing a high-throughput and fully automated system has several advantages over using manual methods. Therefore, this study aimed to evaluate automation efficiency for the detection of HLA-B*27. Peripheral blood samples were obtained from 50 participants, and DNA was isolated from these samples. A Pharmigene PG27 detection kit was used for the qualitative detection of HLA-B*27. The performances of the semi-automated and fully automated LabTurbo^TM AIO systems in the detection of HLA-B*27 were compared. The mean absorbance (optical density) values for the Maelstrom^TM 8 and LabTurbo^TM AIO systems were found to be 1.88 and 1.9, respectively. The housekeeping gene was amplified and quantified using a real-time PCR assay across all DNA extracts to check the quality of the extracted human DNA. The results were expressed as the cycle threshold (Ct) values for all DNA extracts from both platforms. The mean Ct values for the Roche Cobas z480 and LabTurbo^TM AIO systems were found to be 22.7 and 20.4, respectively. This study demonstrated that the semi-automated method and the LabTurbo^TM AIO system yield consistent results for the detection of HLA-B*27. However, compared to the semi-automated method, the LabTurbo^TM AIO system provides standardized procedures, avoids manual handling, and improves turnaround time.

Spondyloarthritis in North Africa: an update

Spondyloarthritis (SpA) has been less well studied than rheumatoid arthritis in North Africa, due to a belief that it is rare and benign in certain populations. The main genetic trait of SpA is its association with human leukocyte antigen (HLA)-B27. The distribution of this allele largely explains the prevalence and severity of SpA. The prevalence of HLA-B27 in the general population of North Africa is estimated at about 4%, and rises to about 60% among people affected with SpA. Coxitis is one of the main features of North African SpA, but the response to treatment is comparable to the literature from the West. The major challenge in North Africa remains accessibility to specialized care and means of early diagnosis. Prevalent infections in North Africa do not seem to be a major obstacle to optimal treatment strategies.

Low frequency of HLA-B27 in ankylosing spondylitis patients from Turkey

OBJECTIVES

Ankylosing spondylitis is strongly associated with HLA-B27. However, the strength of the association with HLA-B27 and the clinical features may vary in different parts of the world. The aim of this study is to compare the clinical features of AS and the frequencies of HLA-B27 and its alleles in patients from Turkey with other series.

METHODS

One hundred and twelve patients (72 male/40 female) fulfilling the modified New York criteria for the classification of AS and 55 (27 male/28 female) healthy controls were typed for HLA-B27 and allele frequencies by sequence specific primer (PCR/SSP) method and assessed for clinical manifestations.

RESULTS

Male to female ratio was 1.8, mean age at disease onset was 23.5 and 24.1% of patients reported juvenile onset of symptoms. Peripheral arthritis was seen in 52.7% of patients. Family history (p=0.01) and peripheral arthritis (p=0.02) were more frequent in females and spinal involvement in males. HLA-B27 was found to be positive in 70% of patients and associated with younger mean age, uveitis and shorter time elapsed from symptom to diagnosis. The frequency of HLA-B27 alleles associated with SpA was not different between ankylosing spondylitis patients and healthy controls.

CONCLUSION

Low frequency of HLA-B27 and clinical variations in ankylosing spondylitis may be due to different genetic and/or environmental factors in Turkey.

A Mariner with Crippling Arthritis and Bleeding Eyes

A 41-year-old mariner developed acute arthritis affecting his legs more than his arms or hands during a violent storm on his return from the first of four voyages of discovery. He experienced repeated attacks of the arthritis over the ensuing 14 years, which on at least two occasions were accompanied by painful eyes "much affected with bleeding." He died shortly before his 55 birthday "quite paralyzed and bedridden." Who was he, and what was the likely etiology of his disorder?

HLA-B27 genotyping by Fluorescent Resonance Emission Transfer (FRET) probes in real-time PCR

Several polymerase chain reaction (PCR)-based human leukocyte antigen (HLA) genotyping methods are in use, but none is fully satisfactory. The introduction of real-time PCR (rt-PCR) with fluorescence resonance energy transfer (FRET) probes provides a powerful tool to overcome the drawbacks of current methods such as the long processing time and the requirement for post-PCR manual procedures. Here we present evidence that the FRET-fluorotyping principle may resolve HLA-B27 variants, providing a higher resolution in less time than the techniques currently in use. The protocol uses between one and three consecutive amplification reactions depending on the resolution required. The first reaction, aimed at detecting HLA-B27-positive samples, uses beta-globin coamplification as control. The second reaction, aimed at resolving most frequent B27 alleles, uses two hybridization probes whose melting temperatures curves allow the classification of HLA-B27 alleles into eight groups. By adding a third reaction, even the rarest alleles associated and not associated to ankylosing spondylitis (AS) may be discriminated. The technique was blindly tested on 60 samples from individuals previously typed and confirmed by standard PCR sequence-specific oligoprobes-PCR sequence and PCR-based typing PCR-SBT (30 B27+, 30 non-B27). There was a complete concordance rate, thus confirming the potential of this new technique for clinical HLA-B27 typing and for HLA typing in general.

Polymorphism of HLA-B27 in Taiwanese Chinese

Heterogeneity of HLA-B27 is represented by a family of 24 closely related alleles/subtypes. Frequency and disease association of these alleles with spondyloarthropathies differ among ethnic groups. Accurate investigation of frequencies of alleles is often hindered by the size and demographic region of sample tested. With an ever-increasing number of B27 alleles being discovered, it is becoming imperative to establish disease association of each individual alleles and its biological importance. In a large number of normal healthy Taiwanese Chinese individuals (75,777) tested nationally, over a period of five years, in a single immunogenetics centre, we found additional B27 subtypes not revealed in a previous Taiwanese Chinese population study. The subtypes found in Taiwanese Chinese and the frequencies of each of the subtypes are reported.

Low frequency of HLA-B*2706 in Taiwanese patients with ankylosing spondylitis

The presence of HLA-B27 in patients affected with ankylosing spondylitis (AS) was well established prior to the advent of DNA typing of various genes within the major histocompatibility complex (MHC) in humans. However, molecular typing of the MHC genes revealed that B27 comprises a motley assortment of alleles, some of which are strongly positively associated with the disease and some of which are negatively associated with the disease. B*2706 was reported to have a negative association with AS in the Thai population and in Chinese Singaporeans. We report here our finding of an absence of B*2706 in 184 Taiwanese AS patients.

B*27 in molecular diagnostics: impact of new alleles and polymorphism outside exons 2 and 3

HLA-B*27 is known to be associated with ankylosing spondylitis and several methods have been applied to determine its presence or absence. In this report two molecular methods were used for detection of B*27. The polymerase chain reaction sequence-specific primer (PCR-SSP) method was performed to detect the presence or absence of B*27, whereas the sequence-based typing method (SBT) was used to identify the B*27 subtype. The PCR-SSP method used to detect B*27 was updated to enable the detection of all B*27 alleles. The typing results obtained by this method were compared with the serological typings of 262 individuals. Fifty of them were found to be B*27 positive by PCR-SSP and 46 also showed positive serological reactions with B27-specific sera. The four discrepancies were the result of the presence of B*2712 in three individuals and B*2715 in one individual; both alleles showed no serological reactions with B27-specific antisera. With SBT the sequences of exons 1 through 4 were determined to unequivocally assign the B*27 alleles. Eleven different subtypes were detected in 78 individuals, including three new B*27 alleles: B*27054, B*2715 and B*2717. The allele B*27054 showed an allelic drop out when exon 3 was amplified. Three differences with B*27052 were demonstrated; one in exon 1, one in intron 1 and one in intron 2, the latter being responsible for the allelic drop out. The B*2715 allele was serologically not detectable with several B27-specific sera, but showed Bw4-positive reactions. The sequence of B*2715 showed two mismatches with B*2704. The sequence of B*2717 showed one mismatch with B*27052 at position 248 (A-->T), which was considered to be a conserved position in all B alleles.

HLA-B27 polymorphism

HLA-B27 is a serologic specificity that encompasses 25 different alleles that encode 23 different products (proteins): HLA-B*2701 to B*2723. These alleles are also called subtypes of HLA-B27, and they may have evolved from the most widespread subtype, B*2705. These subtypes are distinguished from changes mostly in exons 2 and 3, which encode the alpha 1 and alpha 2 domains of the B27 molecule, respectively. Occurrence of ankylosing spondylitis (AS) or related spondyloarthropathy (SpA) has thus far been documented in subjects possessing any one of the first ten (B*2701 to B*2710) subtypes studied. However, B*2706 in Southeast Asian and B*2709 in the Italian island population of Sardinia seem not to be associated with AS. The 13 most recent subtypes have not yet been studied for disease association. It is important to investigate which of them are and are not associated with AS and related SpA, and whether certain subtypes show any preferential association with some of the clinical features or forms of these diseases among the various ethnic/racial populations and geographic regions of the world. This is expected to provide clues as to the mechanism of disease association, and one of the strongest reasons to study the B27 subtypes is to learn the effects of the sequence variations on the peptide-binding specificity of the molecule. Among these peptides may be the putative arthritogenic peptide(s).

HLA-B27 and genetic predisposing factors in spondyloarthropathies

With the mapping of the human genome having been completed, our ability to investigate and ideally better understand the genetic basis of rheumatic diseases is advancing at a rapid pace. Substantial evidence strongly favors a direct role for HLA-B27 in genetic susceptibility to ankylosing spondylitis and related spondyloarthropathies, although the underlying molecular basis has yet to be identified. HLA-B27 contributes only 16 to 50% of the total genetic risk for the disease, clearly indicating that other genes must be involved. However, no other putative disease genes have yet been absolutely proven. Potential genes include MHC (HLA class II, low molecular weight proteasome [LMP], transporter associated with antigen processing (TAP), tumor necrosis factor [TNF]-alpha, and major histocompatibility complex class I chain-related gene A (MICA), as well as non-MHC genes (IL-1RA, IL-6, IL-10, and CYP2D6). Genome-wide screens have identified other chromosomal areas of interest: 1p, 2q, 6p, 9q, 10q, 16q, and 19q. However, different studies have given conflicting results. HLA-B27 itself is a serologic specificity, which encompasses 25 different alleles that encode 23 different products (proteins): HLA-B*2701 to B*2723. These alleles may have evolved from the most widespread subtype, B*2705, and two of them, B*2706 in Southeast Asia and B*2709 in Sardinia, seem not to be associated with ankylosing spondylitis. The distinction between the disease associated and nonassociated subtypes may provide clues to the actual role of B27 in disease pathogenesis.

Update: the twenty subtypes of HLA-B27

HLA-B27 is a serologic specificity that encompasses 20 different alleles-HLA-B*2701 to B*2720. These alleles are also called subtypes of HLA-B27, and they have evolved from the B*2705 subtype, mostly from changes in exons 2 and 3 (which encode the alpha 1 and alpha 2 domains of the peptide binding groove, respectively). Occurrence of ankylosing spondylitis (AS) or related spondyloarthropathy (SpA) has thus far been documented in subjects possessing any one of the first 10 subtypes. However, B*2706 in Southeast Asian and B*2709 in the Italian island population of Sardinia may have a relatively much weaker association with AS. The 10 most recent subtypes have not yet been studied for disease association. There may exist a hierarchical ranking, resulting, in part, from differences in other co-inherited genetic factors, or due to environmental factors; eg, B*2705 is clearly disease-associated throughout the world, but not among the West Africans of Senegal and Gambia. It is important to investigate whether certain subtypes show any preferential association with some of the clinical features or forms of AS and related SpA among the various ethnic/racial populations and geographic regions of the world. This may help to identify the polymorphic positions of HLA-B27 that may have a disease-predisposing role.