Recurrent extended HLA haplotypes in children with selective IgA deficiency

The Role of HLA in the Association between IgA Deficiency and Celiac Disease

Selective IgA deficiency (SIgAD) is the most frequent primary immune defect. Since SIgAD is not characterized by relevant infectious issues in most cases, it is often diagnosed during the diagnostic work up of several and different autoimmune disorders, which are associated with this primary immune defect. The genetic background of SIgAD is complex and three HLA haplotypes resulted to be more frequently associated with it; in detail, two of them include HLA-DQB1^∗02 allelic variants, which are essential predisposing factors to develop Celiac Disease (CD). Here, we discuss the evidence regarding the role of HLA in the etiopathogenesis of SIgAD and its association with CD. Actually, the HLA region seems to play a modest role in the genetic predisposition to SIgAD and we may speculate that the association with the HLA-DQB1^∗02 alleles (or haplotypes including them) could derive from its link with CD. Indeed, SIgAD and some related immunological alterations are likely to predispose to several autoimmune diseases (with and despite different HLA backgrounds), including CD, which is relatively common and directly associated with the HLA-DQB1^∗02 allelic variants coding the DQ2 heterodimer. Further and specific studies are needed to make final conclusions in this regard.

The Epidemiology and Clinical Manifestations of Autoimmunity in Selective IgA Deficiency

Selective immunoglobulin A deficiency (SIgAD) is the most common primary immunodeficiency, defined as an isolated deficiency of IgA (less than 0.07 g/L). Although the majority of people born with IgA deficiency lead normal lives without significant pathology, there is nonetheless a significant association of IgA deficiency with mucosal infection, increased risks of atopic disease, and a higher prevalence of autoimmune disease. To explain these phenomena, we have performed an extensive literature review to define the geoepidemiology of IgA deficiency and particularly the relative risks for developing systemic lupus erythematosus, hyperthyroidism, hypothyroidism, type 1 diabetes mellitus, Crohn's disease, ulcerative colitis, rheumatoid arthritis, juvenile idiopathic arthritis, ankylosing spondylitis, and vitiligo; these diseases have strong data to support an association. We also note weaker associations with scleroderma, celiac disease, autoimmune hepatitis, immune thrombocytopenic purpura, and autoimmune hemolytic anemia. Minimal if any associations are noted with myasthenia gravis, lichen planus, and multiple sclerosis. Finally, more recent data provide clues on the possible immunologic mechanisms that lead to the association of IgA deficiency and autoimmunity; these lessons are important for understanding the etiology of autoimmune disease.

Caucasian origin of disease associated HLA haplotypes in chinese blood donors with IgA deficiency

PURPOSE

Selective immunoglobulin A deficiency (IgAD) is the most common primary immunodeficiency in Caucasians with a prevalence of 1:600. However, the prevalence of IgAD is markedly lower in East Asian countries but no genetic studies have been performed on IgAD individuals in the Mongoloid population.

METHODS

We investigated the prevalence of IgAD in a large number of Chinese blood donors (n = 39,015) in Shanghai, China. We measured immunoglobulin class, IgG subclass and anti-IgA serum levels among the IgAD donors. These donors were subsequently tissue typed and the allele frequency was compared with the Shanghai bone marrow donor HLA registry.

RESULTS

Seventeen IgAD Chinese blood donors were identified, giving a prevalence of 1: 2,295. Two previously identified IgAD blood donor samples were added in the subsequent tests. Most IgAD donors had serum IgG levels above the normal range with no major IgG subclass deficiency and one donor was weakly positive for anti-IgA. Two-thirds of the Chinese IgAD donors carried Caucasian IgAD associated risk haplotypes, including DRB1*0301-DQB1*0201, DRB1*0701-DQB1*0202 and DRB1*0102-DQB1*0501, giving a significantly higher frequency of these haplotypes as compared to the Shanghai bone marrow donor HLA registry.

CONCLUSIONS

The prevalence of IgAD in Chinese in this study is markedly lower than in Caucasians. This is the first study to investigate the genetics of IgAD in the Mongoloid population and two-thirds of the Chinese IgAD donors showed a mixture of Caucasian IgAD risk haplotypes. The low prevalence of IgAD could potentially be due to the low frequency of the disease associated risk haplotypes in China.

Association of HLA-*08:DRB1*03 with immunoglobulin A-deficiency

OBJECTIVE

Susceptibility to IgA deficiency (IgAD) is strongly associated with alleles of HLA, but it is not equally strong in different human populations. Therefore, the goal of this study was to determine the HLA-A, -B and -DRB1 antigenic and haplotypic frequencies in unrelated Polish Caucasian IgA-deficient patients who had never been examined so far in this respect.

METHODS

The HLA alleles were determined by means of low resolution polymerase chain reaction with sequence specific primers (PCR-SSP) method in a group of IgA-deficient patients and control subjects from the same area.

RESULTS

The HLA-DRB1*03 allele showed the strongest association with IgA deficiency in the Polish population (OR=6.6, p cor=0.0084). The HLA-B*08 allele was also associated with predisposition to the disease (OR=6.22, p cor=0.033). These significant associations could be explained in the context of a positive association of IgAD with the HLA-B*08:DRB1*03 haplotype, previously reported in other Caucasoid populations from Northern and Central Europe. In our group the HLA-B*08:DRB1*03 haplotype was present in 52.9% of IgA-deficient patients comparing to 9.9% in controls (p< 0.00011). A positive association of HLA-B*08 and DRB1*03 was stronger in IgA-deficient males than in females from the same group.

CONCLUSION

Immunoglobulin A deficiency in Polish population is strongly associated with HLA-B*08:DRB1*03 haplotype rather than with single alleles.

Major histocompatibility complex haplotypes in Spanish immunoglobulin A deficiency patients: a comparative fine mapping microsatellite study

The most consistent finding in Immunoglobulin A deficiency (IgAD) genetics is the presence of susceptibility factors located in the major histocompatibility complex (MHC). We have described the existence of at least two distinct susceptibility genes in the MHC present in different haplotypes. The aim of the present study was to locate with precision the susceptibility genes present in DR1- and DR7-positive haplotypes, taking advantage of their structural diversity, as opposed to the conserved nature of the DR3-extended susceptibility haplotype (DR3/B8), that hampers a more exhaustive scrutiny. A detailed analysis with 20 markers along the MHC in the 400 haplotypes present in 100 IgAD families, with special density at Class II locations, was performed to define the minimal shared susceptibility region present in all haplotypes carrying DR1 and, on the other hand, in all DR7-positive haplotypes. A comparison of the fine microsatellite allele structure of DR-extended haplotypes in the Spanish population with those described for Swedish and British families revealed no difference in DRB1*0101 and DRB1*0102 haplotypes between both populations. Our data suggest that the etiologic mutation present in DRB1*0101 and DRB1*0102 in North Europe (Sweden and UK) is missing in the Spanish DRB1*0101 haplotypes but is present in the DQB1/DRB1 region in DRB1*0102 haplotypes. The results obtained also indicated that the most likely susceptibility gene in the DR7 haplotypes is either DQA1 or DRB1.

MHC susceptibility genes to IgA deficiency are located in different regions on different HLA haplotypes

Familial predisposition to IgA deficiency (IgAD) suggests that genetic factors influence susceptibility. Most studies support a polygenic inheritance with a susceptibility locus (designated IGAD1) in the MHC, but its exact location is still controversial. This study aimed to map the predisposing IGAD1 locus (or loci) within the MHC by investigating the pattern of association of the disease with several markers in the region. DNA-based techniques were used to type individual alleles of four polymorphic HLA genes (HLA-DR, -DQA1, -DQB1, and HLA-B), six microsatellites (all located between HLA-DR and HLA-B), and three single nucleotide polymorphisms on the TNF gene. The frequencies of these alleles were compared among ethnically matched populations comprising 182 patients and 343 controls. Additionally, we investigated parents and siblings of 100 of these patients. All four parental haplotypes were established in each family (n = 400), and transmission disequilibrium tests were performed. Surprisingly, our results did not support the hypothesis of a unique susceptibility gene being shared by all MHC susceptibility haplotypes. On HLA-DR1 and -DR7-positive haplotypes IGAD1 mapped to the class II region, whereas on haplotypes carrying HLA-DR3 the susceptibility locus mapped to the telomeric end of the class III region, as reported previously. Our results show how, in complex diseases, individuals may be affected for different genetic reasons and a single linkage signal to a region of a chromosome may actually be the result of disease-predisposing alleles in different linked genes in different pedigrees.

Tumor necrosis factor genomic polymorphism in Spanish IGA deficiency patients

Selective IgA deficiency (IgAD) is the most common form of primary immunodeficiency. Its association with genes within the major histocompatibility complex (MHC) has been repeatedly reported. Recently the susceptibility gene has been located in the class III region, around the tumor necrosis factor (TNF) cluster. In this study we have examined IgAD association with TNF-alpha gene promoter polymorphisms and TNFa and b microsatellites. No significant association was found with the former polymorphisms and the observed associations with TNFa2 allele and haplotypes TNFa2b1 and TNFa2b3 were proven to be secondary to their occurrence on the B14-DR1 and B8-DR3 haplotypes, previously reported to be associated with susceptibility to IgAD. However, a primary negative (protective) association was found between the TNFa10 allele and IgAD.

Genetic linkage of IgA deficiency to the major histocompatibility complex: evidence for allele segregation distortion, parent-of-origin penetrance differences, and the role of anti-IgA antibodies in disease predisposition

Immunoglobulin A (IgA) deficiency (IgAD) is characterized by a defect of terminal lymphocyte differentiation, leading to a lack of IgA in serum and mucosal secretions. Familial clustering, variable population prevalence in different ethnic groups, and a predominant inheritance pattern suggest a strong genetic predisposition to IgAD. The genetic susceptibility to IgAD is shared with a less prevalent, but more profound, defect called "common variable immunodeficiency" (CVID). Here we show an increased allele sharing at 6p21 in affected members of 83 multiplex IgAD/CVID pedigrees and demonstrate, using transmission/diseqilibrium tests, family-based associations indicating the presence of a predisposing locus, designated "IGAD1," in the proximal part of the major histocompatibility complex (MHC). The recurrence risk of IgAD was found to depend on the sex of parents transmitting the defect: affected mothers were more likely to produce offspring with IgAD than were affected fathers. Carrier mothers but not carrier fathers transmitted IGAD1 alleles more frequently to the affected offspring than would be expected under random segregation. The differential parent-of-origin penetrance is proposed to reflect a maternal effect mediated by the production of anti-IgA antibodies tentatively linked to IGAD1. This is supported by higher frequency of anti-IgA-positive females transmitting the disorder to children, in comparison with female IgAD nontransmitters, and by linkage data in the former group. Such pathogenic mechanisms may be shared by other MHC-linked complex traits associated with the production of specific autoantibodies, parental effects, and a particular MHC haplotype.

DNA typing of DQ and DR alleles in IgA-deficient subjects

IgA deficiency (IgA-D) represents the most common immunodeficiency syndrome of infancy. In most cases IgA-D represents an isolated immunological disorder, while sometimes it is associated with IgG subclass deficiency or with the presence of autoantibodies. We investigated the pattern of association of IgA-D with DRB1 and DQB1 loci of the HLA region by DNA molecular typing, which allows the identification of previously serologically undefined specificities. We also compared the gene frequency of DRB1 and DQB1 allelic variants between IgA-D subjects with or without serum autoantibodies. Our results indicate that the gene frequency of the DRB1*0102 subtype and of the DRB1*0102, DQB1*0501 haplotype is significantly higher in IgA-D than in the general population. Furthermore, the IgA-D subjects with autoantibodies showed a positive association with DR4 and DR13 subtypes, thus supporting the hypothesis that genetic factors are also involved in the association between IgA-D and autoantibodies.

Molecular analysis of CYP21 gene mutations carried on HLA-B14 positive haplotypes

HLA-B14 positive haplotypes have increased frequencies in a group of patients with puberty disorders, IgA deficiency and cancer of the ovary. Clinical investigations demonstrated that all these patients have high values of 170H progesteron after the ACTH test which suggests an alterated function of 21 hydroxylase enzyme. In order to investigate whether these B14 positive haplotypes carry the same CYP21 mutation in the various diseases and controls, we have amplified by polymerase chain reaction (PCR) the sections of CYP21B gene which include amino acid positions 172 and 281 where typical mutations are known to occur in 21 hydroxylase deficiency. The presence or absence of the defined mutations was tested by oligonucleotide hybridization using oligonucleotides, labelled with DIG-ddUTP, designed to hybridize with the mutated or with the normal sequence. It was found that regardless of whether the subject tested was a patient or a healthy control the mutation at position 281 was found in all cases carrying HLA-B14, DR1 haplotype. Interestingly, this mutation does not seem to be in association with HLA-B14, DR7 haplotype. These findings suggest that CYP21 gene plays a role in all these differing diseases although it must be stressed that there may be alternative explanations for the observed data.

Shared HLA class II-associated genetic susceptibility and resistance, related to the HLA-DQB1 gene, in IgA deficiency and common variable immunodeficiency

Most cases of selective IgA deficiency (IgA-D) and common variable immunodeficiency (CVID) occur sporadically. However, familial clustering is not uncommon, and the two disorders can occur within the same family. We have previously described positive associations with three DR-DQ haplotypes as well as a strong negative association with DRw15,DQw6,Dw2 in IgA-D. Different amino acids at position 57 of the HLA-DQ beta chain were found to be related to susceptibility and resistance to IgA-D. Now we have found identical, although somewhat weaker, positive and negative DR-DQ associations in a large group of CVID patients (n = 86), as well as the same associations with codon 57 of the DQB1 gene. In addition, we have confirmed our earlier observations in an independent group of IgA-D individuals (n = 69), and in sib-pair analysis we have found linkage of the genetic susceptibility to IgA-D to the HLA class II region. In IgA-D individuals not carrying the three overrepresented DR-DQ haplotypes, the same positive association with a non-aspartic acid residue at position 57 of the HLA-DQ beta chain was seen. The previously reported associations with deletions of the HLA class III genes C4A (fourth component of complement) and CYP21P (steroid 21-hydroxylase pseudogene) were, in our groups of immunodeficient individuals, statistically secondary to the association with the DQB1 allele 0201. The shared HLA class II associations in the two humoral immunodeficiencies support the hypothesis that IgA-D and CVID are related disorders. Disease susceptibility and resistance are most closely associated with a gene(s) within the DR-DQ region, alleles of the DQB1 locus being candidate genes.

Transient IgG subclass deficiencies in newly diagnosed diabetic children

In 27 children (15 males and 12 females) with insulin-dependent diabetes mellitus (IDDM), aged 1.2-13.5 years (mean 9.9 +/- 3.6 years) we investigated immunoglobulins (IgG, IgA, IgM), IgG subclass levels and islet-cell antibodies (ICA) at diagnosis and at 6 and 12 months after disease onset. At diagnosis, IgG levels were lower than -2SD in 7 patients (26%), IgA in 1 (3.7%), IgM in 1 (3.7%). IgG subclass levels were below the 3rd percentile in 13 patients (48.1%); in particular IgG1 in 7 (26%), IgG2 in 3 (11.1%), IgG3 in 2 and IgG4 undetectable in 1 case. In 3 out of the 13 patients combined IgG1-IgG3, IgG1-IgG2 and IgG1-IgG4-IgA deficiencies were observed. ICA were greater than 20 Juvenile Diabetes Foundation units in 17/27 patients. The HLA-DR2 frequency was higher in patients with IgG subclass deficiency than in patients with normal IgG subclass levels. During follow up, IgG levels normalized in 6 patients while IgA and IgM did not change. IgG1 normalized in 5 out of the 7 patients, IgG2 in all patients while IgG3 and IgG4 did not change. One year later ICA were still present in 8/27 patients. The hypogammaglobulinaemia and IgG subclass deficiencies observed in our patients could have either a genetic or an acquired basis.

The genetics of IgG4 deficiency: role of the immunoglobulin heavy chain constant region and HLA loci

IgG4 deficiency is very common (1/400 in the Italian population) and provides a good model for analyzing the genetic factors involved in Ig subclass deficiencies. We have previously reported an association between some immunoglobulin heavy chain constant region (IGHC) polymorphisms and the IgG4 deficiency. The associated polymorphisms spanned the region between the GP and the G4 genes. A larger sample composed of 50 healthy blood donors with IgG4 deficiency (less than 0.001 g/l IgG4), not carrying homozygous gene deletions, together with 82 first-degree relatives is now examined. The results confirmed the association of the deficiency with IGHC polymorphisms, and detected a new association with the HLA-D locus with a strong additive effect between the two systems. However, despite these associations and a highly significant risk for IgG4 deficiency within families, close linkage with either IGHC or HLA loci was not apparent by the affected sib pair method. These findings suggest that several concomitant, possibly cooperating, genetic factors may be involved in IgG4 deficiency.

Different amino acids at position 57 of the HLA-DQ beta chain associated with susceptibility and resistance to IgA deficiency

The human leukocyte antigens (HLA) are implicated in the genetic susceptibility to a large number of diseases. Some of the diseases associated with HLA class II are related to specific amino acids or epitopes of the domain of the HLA class II molecule that is distal to the membrane. In man, selective immunoglobulin A deficiency is the most common immunodeficiency, frequently resulting in recurrent sino-pulmonary infections and gastro-intestinal disorders. Associations have been described with HLA class I, and to a lesser extent with different class II alleles, which might indicate that they share some common feature. Here we study 95 IgA-D patients and find positive associations with three DR-DQ haplotypes and a strong negative association with a fourth haplotype. Comparison of the sequences of the polymorphic amino-terminal domain of the DQ beta chain showed that the three 'susceptibility' haplotypes all had a neutral alanine or valine at position 57. The 'protective' allele had the negatively charged aspartic acid at this position (Asp57). Codon 57 of the HLA-DQ beta chain has been implicated in the susceptibility to insulin-dependent diabetes mellitus. Our data suggest that the same amino acid position could possibly also influence susceptibility and resistance to selective immunoglobulin A deficiency.

Central MHC genes, IgA deficiency and autoimmune disease

IgA deficiency is a common immunological disorder that is sometimes associated with an immunodeficiency syndrome, allergic disease, autoimmune disease and gluten enteropathy. Many subjects with this deficiency, however, are healthy, at least for many decades. Analysis of the immunological and genetic abnormalities found in IgA deficiency and in some of the associated disorders has led to the postulate that a genetically determined defect of immunoregulation underlies all of these diseases. Here, Martyn French and Roger Dawkins propose that the products of genes located within the central region of the major histocompatibility complex (MHC) regulate B cells and/or antibody production. Particular MHC ancestral haplotypes contain specific alleles and arrangements of these genes, thereby explaining associations with either increased or decreased production of immunoglobulin isotypes by B cells.