Gm allotypes in Swedish myasthenia gravis patients

Genetics of autoimmune myasthenia gravis, a model for antibody-mediated autoimmunity in man

Autoimmune myasthenia gravis is an antibody-mediated autoimmune disease of the neuromuscular junction aimed at the muscle acetylcholine receptor. Recent genetic analyses focusing on a nonclass II HLA-linked locus, MYAS1, and on one of the genes encoding the AChR self-antigen, CHRNA1, are discussed.

Autoimmunity to ryanodine receptor and titin in myasthenia gravis is associated with GM allotypes

Myasthenia gravis (MG) is mediated by autoantibodies against the acetylcholine receptor at the muscle endplate. Some MG patients have in addition antibodies (Ab) to the skeletal muscle proteins ryanodine receptor (RyR) and titin. We have examined GM and KM allotypes, RyR and titin Ab in 44 MG patients (37 thymoma patients and 7 non-thymoma, late-onset patients) and 292 non-MG controls to see if GM/KM allotypes associate with differences in autoantibody production. All patients had titin Ab, and 15 thymoma patients had also RyR Ab. The phenotype GM 1, 2, 3 23 5, 21 was significantly increased in the patients with titin Ab compared with the non-MG controls (chi2 = 4.93, p < 0.05). Thymoma patients with RyR Ab had a higher frequency of the GM 3 23 5 phenotype compared with RyR Ab negative patients and controls (chi2 = 7.1, p < 0.05). KM allotypes did not differ between RyR Ab positive or titin Ab positive patients and controls. GM phenotypes may thus be associated with an autoimmune response against the muscle proteins titin and RyR in MG patients.

Immunoglobulin allotypes (GM and KM) and their interactions with HLA antigens in autoimmune diseases: a review

GM and KM immunoglobulin (Ig) allotypes and their interactions with HLA antigens have been analyzed in various autoimmune diseases: multiple sclerosis, rheumatoid arthritis, insulin-dependent diabetes mellitus (IDDM), systemic lupus erythematosus, coeliac disease, Crohn's disease, Graves' disease, atrophic thyroiditis, Hashimoto's thyroiditis, myasthenia gravis, chronic active hepatitis, alopecia areata, uveitis, vitiligo, Turner's syndrome, glomerular nephritis, Berger's disease and idiopathic dilated cardiomyopathy. This review reports published results about associations or linkages, as well as the origins of the populations, the numbers of patients and controls tested. The possible role of Ig polymorphisms in the physiopathology of autoimmune diseases is discussed. Ig allotypes and statistical methods used to analyse the HLA and Ig data are also described.

Identification by genomic typing of non-DR3 HLA class II genes associated with myasthenia gravis

HLA association with myasthenia gravis (MG) has been studied in a series of 114 patients using class I and class II genotyping after PCR amplification. Positive association was found with DR3, particularly in women (RR = 2.6) and in early MG onset (RR = 3.4). DRB1, DRB3, DQB1, DQA1 and B (B8 and B18) genotyping revealed that the association was predominantly with the B8 DRB1*03 DRB3*0101 DQB1*0201 DQA1*0501 ancestral haplotype. This haplotype frequency was also increased in patients with thymic hyperplasia (RR = 3.5) and was greatly reduced in patients with thymoma (RR = 0.35). Sixteen out of 48 patients carrying this 8.1 ancestral haplotype showed absence of B8 (n = 4) or of DR3 (n = 12). HLA class II genotyping further revealed the existence of two other significant associations. MG was positively associated with the DQB1*0604 allele (RR = 3.4), particularly in patients with thymoma (RR = 5.7). Furthermore, the disease was negatively associated with DR1 in females (RR = 0.32). These data suggest that MG is placed under the control of at least three distinct genes: (1) a class II predisposing gene in the 8.1 ancestral haplotype; (2) a thymoma-associated class II allele on the DQB1*0604 haplotype; and (3) a protective allele DR1.

Immunoglobulin heavy chain gene associations in myasthenia gravis: new evidence for disease heterogeneity

Susceptibility to myasthenia gravis (MG) is known to involve genes residing in the major histocompatibility complex class I and II regions (HLA-B8 and DR3). Immunoglobulin heavy chain constant region (IgCH) allotypes have also shown some associations with MG. We have used restriction fragment length polymorphism analysis with probes to the IgCH switch (S) regions mu and alpha 1 and the downstream marker D14S1 to investigate 189 Caucasoid patients with well-defined MG. A highly significant increase in the frequency of the 2.6 kilobase (kb) S mu homozygous genotype and the 2.6 kb S mu allele was found in patients with disease onset after the age of 40 years (late onset) compared with normal controls (P less than 0.00075 and P less than 0.025 respectively). No association was found at the S alpha 1 or D14S1 loci. In patients with an associated thymoma there was a moderate increase in the frequency of the 2.6 kb S mu and 7.4 kb S alpha 1 genotypes. These results independently support the previous separation of the late-onset subgroup. Finally, the stronger association at S mu rather than at the downstream S alpha 1, Gm and D14S1 loci suggest that the genes predisposing to MG are located within the variable region of the Ig heavy chain loci.

The contribution of non-MHC genes to susceptibility to autoimmune diseases

Genetic studies of experimental models of autoimmune diseases, including systemic lupus-like syndromes and organ-specific autoimmunity, provide major information on genetic control of autoimmune diseases. In addition to genes known to be linked to the major histocompatibility complex (MHC), these studies point to multiple genes located outside the MHC that influence the onset and the progression of autoimmune diseases. Identification of these genes and of their interrelationships is now a major task that will be facilitated by recent progress in molecular biology and gene mapping. Among candidate genes, antigen-receptor genes (i.e., immunoglobulin- and T-cell receptor genes) most likely contribute an important part of the autoimmune susceptibility in several of these animal models. Available linkage data suggest a similar involvement of these antigen-receptor genes in several human autoimmune diseases. In addition to a better understanding of pathogenic mechanisms associated with autoimmunity, the knowledge of these disease-predisposing genes is expected to permit a better classification of often complex syndromes as well as the design of new treatments.

Immunoglobulin allotypes in myasthenia gravis patients with a thymoma

Gm and Km allotypes were examined in 29 myasthenia gravis patients with a thymoma and non-receptor skeletal muscle antibodies. The frequency of the phenotype Gm1,2,3;23;5,21 was significantly higher in the patients than in 292 healthy controls (P less than 0.01). Km allotype frequencies did not differ in patients and controls.

Immunoglobulin genes, HLA-B8/DR3, and immune responsiveness to primary immunogen and mitogens in normal subjects

The genetic regulation of immune responsiveness by genes from two independent, highly polymorphic genetic systems, namely immunoglobulin allotypes and human leukocyte antigens (HLA), was studied in 35 healthy Caucasian volunteers. The in vivo IgG class antibody response to the primary test immunogen alpha-helix pomatia hemocyanin (HPH) was increased in subjects with the Gm1,17;..;21 haplotype compared to that of the non-Gm1,17;..;21 group. The IgM-class response tended to be higher in the former group. Levels of in vivo IgA-class-specific anti-HPH antibodies tended to be higher in the group of individuals positive for HLA-B8/DR3 than in the non-B8/DR3 group. This difference was statistically significant only in the absence of the Gm1,17;..;21 haplotype. The in vitro lymphocyte proliferative response on mitogenic stimulation with phytohemagglutinin (1 micrograms/ml) and pokeweed mitogen (10 micrograms/ml) also appeared to be associated with both systems. The presence of the Gm1,17;..;21 haplotype was associated with decreased lymphocyte reactivity, whereas the B8/DR3 phenotype was associated with high responsiveness to these mitogens. However, in the presence of the Gm1,17;..;21 haplotype subjects positive for HLA-B8/DR3 did not respond better to mitogenic stimulation than those lacking this HLA haplotype. Our results imply that the immunogenetic make-up of test persons should be taken into account in the assessment of the immune status of individuals or groups of patients.

Immunoglobulin allotypes in caucasian and Chinese myasthenia gravis: differences from Japanese patients

The G2m(n) allotype was significantly increased in Chinese female and high autoantibody cases, and in caucasians with pure ocular myasthenia, or undetectable autoantibody. In contrast to the strong Glm(x) association reported in Japanese, no overall Gm haplotype, or Am or Km allotype association was found in 90 (Taiwan) Chinese and 181 caucasian myasthenia gravis patients.

Heterogeneity in myasthenia gravis: HLA phenotypes and autoantibody responses in ocular and generalized types

HLA phenotypes and autoantibody responses were studied in 71 Japanese patients with myasthenia gravis. HLA-A2, Bw61, and DRw9 were associated with ocular myasthenia gravis (corrected p [CP] less than 0.05 relative risk [RR] = 2.88; CP less than 0.02, RR = 3.60; and CP less than 0.001, RR = 4.63, respectively) and HLA-DRw8 was associated with generalized myasthenia gravis (CP less than 0.001, RR = 5.40). Neither HLA-B8 nor DR3 was found in Japanese patients. The titer of antiacetylcholine receptor antibody (AChR Ab) and the incidence of autoantibodies other than AChR Ab were higher in patients with generalized myasthenia gravis than in those with the ocular type (2.77 +/- 0.62 versus 0.17 +/- 0.03 pmol/ml, p less than 0.001; and 60.6 versus 29.0%, p less than 0.02, respectively). Patients with a high titer of AChR Ab or with autoantibodies had an increased frequency of HLA-DRw8 (CP less than 0.02, RR = 4.61, and CP less than 0.005, RR = 4.53, respectively); whereas patients with a low titer of AChR Ab or without autoantibodies had an increased frequency of HLA-DRw9 (CP less than 0.001, RR = 8.26, and CP less than 0.005, RR = 4.08, respectively). These findings suggest that ocular and generalized myasthenia gravis might have different immunogenetic backgrounds.

Immunoglobulin allotypes in patients in end-stage renal failure

In a population of 282 Caucasoid patients in end-stage renal failure (ESRF) Gm and Km typing has confirmed a significant increase in the frequency of the Gm1,2,17;21 haplotype. This was confined to an increase in the number of heterozygous Gm(1,2,3,17;21,5,10,13,14) individuals. A concomitant decrease in the frequency of presumptive Gm(3,5,10,13,14) heterozygotes was also confirmed. Analysis of individual renal diseases revealed significant immunoglobulin allotype, phenotype and haplotype frequency deviations in those patients presenting with hypertension, glomerulonephritis or pyelonephritis. The allotype distribution in patients with physical abnormalities of the urinary-genital tract, whether congenital or acquired, was normal.

Gm allotypes in IgA deficiency

Gm phenotypes were examined in 90 Swedish IgA-deficient (less than 0.05 g/litre of serum IgA) donors and 40 normal first and second degree relatives of six of these donors. The G1m1,2, G3m5 and Km1 frequency in the group of IgA-deficient donors did not differ from that found in the normal population. Among the relatives, HLA and/or Gm identical normal sibs were observed. Anti-IgA antibodies were present in 29 of the IgA-deficient donors and anti-IgG in seven. No association between the two was found. A statistically significant association between the G1m-2 phenotype and the presence of anti-IgA antibodies was observed. When subdivided according to HLA type, a non-random distribution of Gm phenotypes was seen in HLA-B8/DR3 positive individuals with anti-IgA antibodies (HLA-B8/DR3 being the haplotype associated with IgA deficiency). These data suggest an association between IgA deficiency, anti-IgA and the studied Gm allotypes.

Association of immunoglobulin Gm allotypes with antiglomerular basement membrane antibodies and their titer

We studied the immunoglobulin Gm allotypes in 41 patients with glomerular nephritis caused by autoantibodies to glomerular basement membrane (GBM). Gm phenotypes of all 41 patients were attributable to combinations of the 3 Gm haplotypes commonly found in Caucasoid populations; identified by the allotypes Gm 1,21 (ag), Gm 1,2,21 (axg), and Gm 3,5,11 (fb). The incidence of the putative haplotype Gm 1,2,21 (axg) was greatly increased in the patients being present in 22 of 41 (56%) of patients compared to 28 of 167 controls. (Pcor = 1.5 X 10(-5]. The increase in Gm 1,2,21 (axg) was attributable entirely to presumed heterozygotes with the phenotype Gm 1,2,21;3,5,11 (axg;fb), with concomitant decreases in the frequencies of patients with the phenotypes Gm 1,21 (ax) and with Gm 3,5,11 (fb). Heterozygotes at Gm loci had higher titers of anti-GBM antibodies irrespective of the presence of Gm 1,2,21 (axg). Thus genes within or closely linked to the Gm complex in addition to HLA linked genes influence susceptibility to or clinical expression of anti-GBM disease.