Human Complement C4B Allotypes and Deficiencies in Selected Cases With Autoimmune Diseases.

Human complement C4 is one of the most diverse but heritable effectors for humoral immunity. To help understand the roles of C4 in the defense and pathogenesis of autoimmune and inflammatory diseases, we determined the bases of polymorphisms including the frequent genetic deficiency of C4A and/or C4B isotypes. We demonstrated the diversities of C4A and C4B proteins and their gene copy number variations (CNVs) in healthy subjects and patients with autoimmune disease, such as type 1 diabetes, systemic lupus erythematosus (SLE) and encephalitis. We identified subjects with (a) the fastest migrating C4B allotype, B7, or (b) a deficiency of C4B protein caused by genetic mutation in addition to gene copy-number variation. Those variants and mutants were characterized, sequenced and specific techniques for detection developed. Novel findings were made in four case series. First, the amino acid sequence determinant for C4B7 was likely the R729Q variation at the anaphylatoxin-like region. Second, in healthy White subject MS630, a C-nucleotide deletion at codon-755 led to frameshift mutations in his single C4B gene, which was a private mutation. Third, in European family E94 with multiplex lupus-related mortality and low serum C4 levels, the culprit was a recurrent haplotype with HLA-A30, B18 and DR7 that segregated with two defective C4B genes and identical mutations at the donor splice site of intron-28. Fourth, in East-Asian subject E133P with anti-NMDA receptor encephalitis, the C4B gene had a mutation that changed tryptophan-660 to a stop-codon (W660x), which was present in a haplotype with HLA-DRB1*04:06 and B*15:27. The W660x mutation is recurrent among East-Asians with a frequency of 1.5% but not detectable among patients with SLE. A meticulous annotation of C4 sequences revealed clusters of variations proximal to sites for protein processing, activation and inactivation, and binding of interacting molecules.

Clinical features of patients with homozygous complement C4A or C4B deficiency.

INTRODUCTION: Homozygous deficiencies of complement C4A or C4B are detected in 1-10% of populations. In genome-wide association studies C4 deficiencies are missed because the genetic variation of C4 is complex. There are no studies where the clinical presentation of these patients is analyzed. This study was aimed to characterize the clinical features of patients with homozygous C4A or C4B deficiency. MATERIAL AND METHODS: Thirty-two patients with no functional C4A, 87 patients with no C4B and 120 with normal amount of C4 genes were included. C4A and C4B numbers were assessed with genomic quantitative real-time PCR. Medical history was studied retrospectively from patients' files. RESULTS: Novel associations between homozygous C4A deficiency and lymphoma, coeliac disease and sarcoidosis were detected. These conditions were present in 12.5%, (4/32 in patients vs. 0.8%, 1/120, in controls, OR = 17.00, 95%CI = 1.83-158.04, p = 0.007), 12.5% (4/32 in patients vs. 0%, 0/120 in controls, OR = 1.14, 95%CI = 1.00-1.30, p = 0.002) and 12.5%, respectively (4/32 in patients vs. 2.5%, 3/120 in controls, OR = 5.571, 95%CI = 1.79-2.32, p = 0.036). In addition, C4A and C4B deficiencies were both associated with adverse drug reactions leading to drug discontinuation (34.4%, 11/32 in C4A-deficient patients vs. 14.2%, 17/120 in controls, OR = 3.174, 95%CI = 1.30-7.74, p = 0.009 and 28.7%, 25/87 in C4B-deficient patients, OR = 2.44, 95%CI = 1.22-4.88, p = 0.010). CONCLUSION: This reported cohort of homozygous deficiencies of C4A or C4B suggests that C4 deficiencies may have various unrecorded disease associations. C4 gene should be considered as a candidate gene in studying these selected disease associations.

Genetic deficiency in complement component 4b does not alter radiation-induced lung disease in mice.

Previous investigations have shown altered levels of complement components to be associated with radiation-induced lung disease. In this study we aimed to determine whether a deficiency in complement component 4b alters the lung response to irradiation of C57BL/6 mice. The pulmonary phenotype of C57BL/6 C4b(-/-) mice and their wild-type littermates was assessed following an 18 Gy single dose to the thoracic cavity. The assessed end points included, survival time postirradiation, bronchoalveolar lavage cell differential, hydroxyproline measures and histological evidence of alveolitis and fibrosis. The lung phenotype of C4b-deficient mice did not differ from that of wild-type mice in terms of survival time postirradiation, tissue hydroxyproline levels or by histological evidence of alveolitis or fibrosis. No differences in bronchoalveolar cell differential counts were evident among the irradiated mice grouped by C4b genotype. We concluded that a deficiency in C4b does not alter radiation-induced lung disease in the C57BL/6 mouse model.

Genetically determined partial complement C4 deficiency states are not independent risk factors for SLE in UK and Spanish populations.

Systemic lupus erythematosus (SLE) is a chronic, multisystem autoimmune disease. Complete deficiency of complement component C4 confers strong genetic risk for SLE. Partial C4 deficiency states have also shown association with SLE, but despite much effort over the last 30 years, it has not been established whether this association is primarily causal or secondary to long-range linkage disequilibrium. The complement C4 locus, located in the major histocompatibility complex (MHC) class III region, exhibits copy-number variation (CNV) and C4 itself exists as two paralogs, C4A and C4B. In order to determine whether partial C4 deficiency is an independent genetic risk factor for SLE, we investigated C4 CNV in the context of HLA-DRB1 and MHC region SNP polymorphism in the largest and most comprehensive complement C4 study to date. Specifically, we genotyped 2,207 subjects of northern and southern European ancestry (1,028 SLE cases and 1,179 controls) for total C4, C4A, and C4B gene copy numbers, and the loss-of-function C4 exon 29 CT indel. We used multiple logistic regression to determine the independence of C4 CNV from known SNP and HLA-DRB1 associations. We clearly demonstrate that genetically determined partial C4 deficiency states are not independent risk factors for SLE in UK and Spanish populations. These results are further corroborated by the lack of association shown by the C4A exon 29 CT insertion in either cohort. Thus, although complete homozygous deficiency of complement C4 is one of the strongest genetic risk factors for SLE, partial C4 deficiency states do not independently predispose to the disease.

HLA-DRB1 allele frequencies and C4 copy number variation in Finnish sarcoidosis patients and associations with disease prognosis.

Sarcoidosis is a multiorgan immune-mediated disease of unknown etiology with varying clinical pictures. We studied 3 genes in the major histocompatibility complex region (HLA-DRB1 and complement C4A and C4B) in patients with resolved disease after a 2-year follow-up (n = 90) and in patients whose disease was still active at that time point (n = 98) and compared them with controls (n = 150). Our primary aim was to detect genetic differences between the patient groups. We observed that the susceptibility allele for sarcoidosis was HLA-DRB1*15:01 (p = 0.011; odds ratio [OR] = 1.67) and the protective allele was HLA-DRB1*01:01 (p = 0.001; OR = 0.43). HLA-DRB1*03:01 was associated with resolving disease when compared with the persistent group (p = 0.011; OR = 2.22). The probability of having resolving disease was even greater if the patient had HLA-DRB1*03:01 and did not have extrapulmonary lesions (p = 0.001; OR = 3.39). By evaluating amino acid variants of the HLA-DRB1 gene, we determined that specific amino acids in pockets 4, 7, and 9 were associated with the prognosis of sarcoidosis. Our results support the importance of HLA-DRB1 as a predisposing gene for sarcoidosis. Particularly, HLA-DRB1*03:01 and polymorphisms of DRB1 pocket residues were associated with a favorable prognosis. Thus, accurate categorization of disease phenotype and HLA-DRB1 sequencing offer a basis for disease course estimation of sarcoidosis.

Increased frequency of complement C4B deficiency in rheumatoid arthritis.

OBJECTIVE: To assess the copy number variation of complement C4A and C4B genes in patients with rheumatoid arthritis (RA). METHODS: DNA samples were obtained from 299 patients and controls and analyzed for copy number variation of total complement C4, C4A, and C4B genes. The results were compared by chi-square analysis, and odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated. RESULTS: Chi-square analysis revealed similar distribution patterns of total C4 alleles in RA patients (n = 160), non-RA patients (n = 88), and healthy controls (n = 51). There was no trend toward C4A deficiency as in lupus. Significant differences in C4B distribution were observed in RA patients, in whom an ∼2-fold increase in the frequency of homozygous and/or heterozygous C4B deficiency (0 or 1 allele) (40%) was present relative to non-RA patients or healthy controls (both 21.6%). C4B deficiency was more frequent in seropositive RA patients than in seronegative RA patients (44% versus 31%). The odds of C4B deficiency were 2.99 (95% CI 1.58-5.65) (P = 0.0006) in seropositive RA patients relative to non-RA controls. These findings were confirmed in a larger healthy control cohort, yielding an OR of 1.83 (95% CI 1.21-2.76) (P = 0.0056). The association of the shared epitope with C4B deficiency was significantly greater in seropositive RA patients than in non-seropositive RA controls (96% versus 54.5%) (P < 0.0001), suggesting that C4B deficiency interacts with the shared epitope in the development of seropositive RA. CONCLUSION: Our findings indicate a relationship between C4B copy number variation and RA that approximates that seen between C4A copy number variation and lupus. The concurrence of C4B deficiency and the shared epitope in seropositive RA may have broad implications for our understanding of RA pathogenesis.

[Masked deficiency of C4 component of complement in patients with chronic gastrointestinal tract diseases of different etiology].

AIM: Frequency of occurrence detection of C4A and C4B complement system deficiency in patients with chronic gastrointestinal tract (GIT) diseases including gastric ulcer (GU) and duodenal ulcer (DU). MATERIALS AND METHODS: 74 patients with chronic GIT diseases were examined. Endoscopy with stomach mucosa condition evaluation based on histobacterioscopic examination of gastroduodenal biopsy samples was used. Intestine microbiocenosis evaluation was performed by using microflora degree of manifestation according to Federal Standard of Russian Ministry of Health No 231 -91500.11.0004-2003. C4A and C4B isotypes in blood sera of patients were measured by using enzyme immunoassay. RESULTS: Chronic gastroduodenitis was diagnosed in 35.1%, pangastritis B--in 41.9%, GU and DU--in 23% of patients. Histological evaluation of biopsy samples revealed marked inflammatory changes in stomach and duodenum mucosa in 77% of patients. Stomach mucosa infection rate by Helicobacter pylori reached 85%. Microbiological disorders manifestation in microflora of patients matched endoscopic and histobacteriscopic changes in it and was the highest for GU and DU. In 76.0% of cases C4A and C4B isotype deficiency in blood sera matches the development of erosive-ulcerous process in stomach and duodenum mucosa with marked background dysbiotic GIT microbiota disorders. CONCLUSION: Patients with functional deficiency of C4A and C4B isotypes have a genetic burden to susceptibility to chronic GIT diseases whereas H.pylori infection deteriorate the disease.

[Enzyme immunoassay of masked complement component C4 deficiency in patients with urogenital Chlamydia infection].

AIM: Development of new method of C4B isotype functional activity evaluation in enzyme immunoassay by using pharmaceutical preparation derinat as a classical pathway complement activator and its use for blood sera isotyping in confirmed urogenital tract chlamydia infection. MATERIALS AND METHODS: Enzyme immunoassay was used to detect C4A and C4B isotype functional deficiency in blood sera of patients. Chlamydia etiology urogenital infection diagnosis was based on results of standard clinical-instrumental examination methods: vaginal clinical smear analysis, scrape sample light microscopy with consequent treatment by fluorescent monoclonal antibodies against Chlamydia trachomatis and PCR. RESULTS: In acute form of the disease C4A deficiency frequency of occurrence was 0.36, and C4B deficiency - 0.55. In chronic form of the disease deficiency frequency of occurrence was 0.38 for both isotypes. In the group of healthy people isotype deficiency was 0.08 and 0.25, respectively. CONCLUSION: Innate masked C4 deficiency interfere with the normal immune defense of organism against chlamydia infection, and antigen carbohydrate pathogenicity may possibly be more significant for the development of immune response to which C4B isotype activity is necessary.

Familial C4B deficiency and immune complex glomerulonephritis.

Homozygous complement C4B deficiency is described in a Southern European young female patient with Membranoproliferative Glomerulonephritis (MPGN) type III characterized by renal biopsies with strong complement C4 and IgG deposits. Low C4 levels were independent of clinical evolution or type of immunosuppression and were found in three other family members without renal disease or infections. HLA typing revealed that the patient has homozygous A*02, Cw*06, B*50 at the class I region, and DRB1*08 and DQB1*03 at the class II region. Genotypic and phenotypic studies demonstrated that the patient has homozygous monomodular RCCX in the HLA class III region, with single long C4A genes coding for C4A3 and complete C4B deficiency. Her father, mother, son and niece have heterozygous C4B deficiency. The patient's deceased brother had a history of Henoch-Schönlein Purpura (HSP), an immune complex-mediated proliferative glomerulonephritis. These findings challenge the putative pathophysiological roles of C4A and C4B and underscore the need to perform functional assays, C4 allotyping and genotyping on patients with persistently low serum levels of a classical pathway complement component and glomerulopathy associated with immune deposits.

The link of C4B null allele to autism and to a family history of autoimmunity in Egyptian autistic children.

UNLABELLED: The reason behind the initiation of autoimmunity, which may have a role in autism, is not well understood. There is an association between some autoimmune disorders and complement (C) 4B null allele. We aimed to study the association between C4B null allele and autism. In addition, we are the first to investigate the association between this allele and a family history of autoimmune diseases in autistic children. Therefore, we examined the frequency of C4B null allele, by quantitative real-time PCR, in 80 autistic patients and 80 healthy matched-children. The frequency of C4B null allele was significantly higher in autistic patients (37.5%) than healthy controls (8.75%), P<0.001. The frequency of autoimmune diseases in families of autistic children (40%) was significantly higher than healthy children (10%), P<0.001. In addition, a family history of autoimmunity had a significant risk for association with autism (odds ratio=6, 95%, CI=2.5-14.1). C4B null allele had a significant risk for association with autism (odds ratio=6.26, 95% CI=2.55-15.36) and with a family history of autoimmunity (odds ratio=21, 95% CI=6.5-67.8). CONCLUSIONS: the link of C4B null allele to autism and to a family history of autoimmunity may indicate its possible contributing role to autoimmunity in autism.

C4B null alleles are not associated with genetic polymorphisms in the adjacent gene CYP21A2 in autism.

BACKGROUND: Research indicates that the etiology of autism has a strong genetic component, yet so far the search for genes that contribute to the disorder, including several whole genome scans, has led to few consistent findings. However, three studies indicate that the complement C4B gene null allele (i.e. the missing or nonfunctional C4B gene) is significantly more frequent in individuals with autism. Due to the close proximity of the CYP21A2 gene to the C4B locus (3 kb) it was decided to examine samples from autistic subjects, including many with known C4B null alleles for common CYP21A2 mutations. METHODS: Samples from subjects diagnosed with autism and non-autistic controls (controls) previously typed for C4B null alleles were studied. Allele specific polymerase chain reaction (PCR) methods were used to determine 8 of the most common CYP21A2 genetic mutations, known to completely or partially inhibit 21-hydroxylase, the enzyme encoded by the CYP21A2 gene. RESULTS: Although the combined autism and control study subjects had 50 C4B null alleles only 15 CYP21A2 mutations were detected in over 2250 genotypes. Eight mutations were detected in the autistic samples and 7 in the controls. The frequency of CYP21A2 mutations was similar between the autism and control samples. Only one individual (autistic) carried a chromosome containing both C4B null allele and CYP21A2 mutations.

Partial C4 deficiency in juvenile idiopathic arthritis patients.

OBJECTIVES: C4 is encoded by 2 distinct but closely linked loci within the major histocompatibility complex locus on human chromosome 6. C4A deficiencies have been associated with autoimmune disease and C4B with increased frequency of infection. C4 deficiencies have rarely been associated with juvenile idiopathic arthritis (JIA). Our aim was to investigate the prevalence of deficiencies in C4 allotypes in JIA patients. METHODS: We evaluated 61 patients [35 JIA patients, 15 systemic lupus erythematosus patients, 9 rheumatoid arthritis patients, and 2 mixed connective tissue disease (CTD) patients] for C4 deficiency. Genomic DNA was isolated from whole blood and subjected to polymerase chain reaction using sequence-specific primers for C4 allotypes. RESULTS: We found 5 JIA patients with C4 deficiencies. Two IgM rheumatoid factor-positive JIA polyarthritis patients had C4 deficiencies, one with complete C4A deficiency and another with partial C4A and complete C4B deficiency. Two oligoarthritis patients displayed partial C4B deficiencies, and complete C4B deficiency was revealed in 1 IgM rheumatoid factor-negative polyarthritis patient. Three patients had histories of recurrent infections and 2 demonstrated a more severe disease course. Disease controls showed 8 systemic lupus erythematosus patients had partial C4 deficiencies, whereas no deficiencies were revealed in the rheumatoid arthritis or mixed CTD patients. CONCLUSIONS: Defects in the complement system have been implicated in the pathogenesis of CTD. However, the specific role of C4 in JIA is not clear. We demonstrate partial C4 deficiencies in 5 JIA patients. Our findings suggest an association between C4 deficiency and another CTD, JIA, as well as with disease severity and recurrent infections.

[Deficiencies in C4A and C4B isotypes of human complement revealed by isoelectrofocusing and chemical reactivity of activated forms].

An approach is proposed to detect deficiencies in isotypes A and B of the C4 component of human complement, based on the calculation of the ratio of their IEA activities and the ratio of their quantities determined by isoelectrofocusing of their desialated forms with chemiluminescent detection in an immunoblot. The ratios of the quantities and activities of C4A/C4B practically coincided when determined in blood serum of 20 patients, many of which had inherited deficiencies in the C4 component isotypes.

C4B deficiency associated with membranoproliferative glomerulonephritis.

A 10-year-old girl was noted to have microscopic hematuria and proteinuria in 1986. As her urinary abnormalities were persistent, she underwent a renal biopsy on 4 occasions until 2003. Although the appearances of the renal biopsies were strongly suspicious of systemic lupus erythematosus, she never exhibited specific autoantibodies or distinctive symptoms. She received corticosteroid therapy and the urinary findings responded. The 4th component of complement remained low during the period of the observation. Both genotyping and allotyping analysis revealed complete C4B deficiency. Some case reports have mentioned renal disease associated with C4B deficiency and we consider the nephropathy in this case to be related to the C4B deficiency.

Complete deficiencies of complement C4A and C4B including 2-bp insertion in codon 1213 are genetic risk factors of systemic lupus erythematosus in Thai populations.

The complement component C4 is encoded by two genes: C4A and C4B on human chromosome 6p in the major histocompatibility complex (MHC). Most studies have linked the deficiencies in C4 with systemic lupus erythematosus (SLE) in Angio-Irish, North American, Black American, Mexican American, Australian and Japanese populations. Null alleles at either locus (C4AQ0 or C4BQ0) are relatively common in Americans occurring at the C4A and C4B loci in approximately 10% and 16% of normal individuals, respectively. In the present study, we extensively examined the possible association between homozygous C4Q0 and SLE in a large cohort of Thai populations diagnosed as SLE and further attempted to identify the genetic basis of C4Q0. One hundred and eighteen cases of SLE patients and 145 matched controls were genotyped by touchdown PCR. The results confirmed the previous studies that 5.93% (7/118) of C4 null genes: 2.54% (3/118) of C4AQ0 and 3.39% (4/118) of C4BQ0 were found in SLE patients. In contrast to other studies, we found no cases of C4 null genes in normal control (0 from 145 samples). To further investigate the genetic basis of C4 deficiency, all genomic DNAs were also analyzed for 2-bp (TC) insertion at codon 1213 in exon 29 which is a common mutation in many C4A null genes and a novel 1-bp deletion (C) at codon 522 in exon 13 that is common in most C4B null genes. Both mutation results in a flame-shift mutation and premature stop codon using sequence specific primers PCR (SSP-PCR) and direct sequencing. The results showed that there was 2-bp insertion in exon 29 of mutant C4B gene in one SLE patient carrying C4AQ0. There was no 2-bp insertion in exon 29 of both C4A and C4B genes in normal individual and the rest of SLE patients. All patients with C4AQ0 exhibited more than 5 ACR criteria including malar rash, oral ulcers, renal disorder, immunological disorder, anti-nuclear antibody, without hematological disorder. In contrast, all of C4BQ0 SLE patients showed 5 or 6 ACR criteria including hematological disorder, malar rash, oral ulcers, renal disorder, immunological disorder and anti-nuclear antibody. A patient who possesses C4AQ0 and 2-bp insertion in exon 29 of mutant C4B showed 9 ACR criteria but no discoid rash and hematological disorder. In conclusion, both C4AQ0 and C4BQ0 are the strong predisposing factors for SLE in Thais. It was supported by the absence of either C4A or C4B deletion in healthy control. We suggested that the different racial and genetic backgrounds could alter the thresholds for requirement of C4A or C4B protein levels in immune tolerance and regulation.

Increased frequency of C4B*Q0 alleles in patients with Henoch-Schönlein purpura.

Henoch-Schonlein purpura (HSP) is a vasculitis of unknown aetiology, possibly involving immune complexes. The complement system is essential for the clearance of immune complexes. Our aim was to explore the hypothesis that patients with HSP have abnormal complements, contributing to the development of the disease. The study included 56 patients diagnosed with HSP at the Children's Hospital, Iceland between 1984 and 2000, and 98 blood donors as controls. Serum levels of immunoglobulin A, C4A, C4B and mannan-binding lectin were measured and compared between the two groups. C4 null alleles were significantly more common in HSP patients than in controls (P = 0.018) and were carried by 66.1% of the patients compared with 41.2% of the controls. This difference was due to an increased frequency of C4B*Q0 allele in the HSP group (0.25 versus 0.11 in the control group; P = 0.002). The fact that the majority of our patients carried a C4 null allele indicates that children with C4 deficiencies may have an increased risk of developing HSP. This may reflect inadequate complement activity and possibly present an opportunity to identify patients at risk of developing serious morbidity associated with HSP.

Complete complement components C4A and C4B deficiencies in human kidney diseases and systemic lupus erythematosus.

Although a heterozygous deficiency of either complement component C4A or C4B is common, and each has a frequency of approximately 20% in a Caucasian population, complete deficiencies of both C4A and C4B proteins are extremely rare. In this paper the clinical courses for seven complete C4 deficiency patients are described in detail, and the molecular defects for complete C4 deficiencies are elucidated. Three patients with homozygous HLA A24 Cw7 B38 DR13 had systemic lupus erythematosus, mesangial glomerulonephritis, and severe skin lesions or membranous nephropathy. Immunofixation, genomic restriction fragment length polymorphisms, and pulsed field gel electrophoresis experiments revealed the presence of monomodular RP-C4-CYP21-TNX (RCCX) modules, each containing a solitary, long C4A mutant gene. Sequencing of the mutant C4A genes revealed a 2-bp, GT deletion in exon 13 that leads to protein truncation. The other four patients with homozygous HLA A30 B18 DR7 had SLE, severe kidney disorders including mesangial or membranoproliferative glomerulonephritis, and/or Henoch Schoenlein purpura. Molecular genetic analyses revealed an unusual RCCX structure with two short C4B mutant genes, each followed by an intact gene for steroid 21-hydroxylase. Nine identical, intronic mutations were found in each mutant C4B. In particular, the 8127 g-->a mutation present at the donor site of intron 28 may cause an RNA splice defect. Analyses of 12 complete C4 deficiency patients revealed two hot spots of deleterious mutations: one is located at exon 13, the others within a 2.6-kb genomic region spanning exons 20-29. Screening of these mutations may facilitate epidemiologic studies of C4 in infectious, autoimmune, and kidney diseases.

Involvement of C4 allotypes in the pathogenesis of human diseases.

The complement system is an important humoral defense mechanism that plays a relevant role against microbial agents, inflammatory response control, and immunocomplex clearance. Classical complement pathway activation is antibody-dependent. The C4 component participates in the initial step of activation, and C4 expression is determined by 2 pairs of allotypes: C4A and C4B. Deficiencies in C4 allotypes have been associated with several diseases. The aim of the present review is evaluate the reported data in the literature regarding specific C4A and C4B deficiencies and characterize their clinical relevance. We searched the MEDLINE and LILACS databases. Papers referring to total C4 deficiency without allotype evaluation and case reports of primary C4 deficiency were not included. Deficiencies in C4 allotypes have been associated with Mycobacterium leprae infection, erythema nodosum, systemic sclerosis with anti-topoisomerase I antibodies, intermediate congenital adrenal hyperplasia with DR5 genotype, diabetes mellitus type 1 with DR3,4 genotype, and diabetes mellitus with antibodies against islet cells. C4 allotype deficiency is also related to C4B deficiency and autoimmune-associated diseases, such as systemic lupus erythematosus, or diseases with an autoimmune component, such as autism. Some reports associate C4A with thyroiditis after delivery as well as limited and systemic sclerosis without anti-topoisomerase I antibodies. However, the studies with C4A and C4B have been concentrated in isolated populations, and some of the studies could not be reproduced by other authors.

An unequal crossover event in RCCX modules of the human MHC resulting in the formation of a TNXB/TNXA hybrid and deletion of the CYP21A.

The central region of the human major histocompatibility complex contains tandemly arranged genes of RP, C4, CYP21, and TNX. The C4 gene region is prone to rearrangements that generates duplications, conversions, and deletions. Diversity in gene number and size causes reorganization and may lead to genetic disorders. The RP, C4, CYP21, and TNX genes form a genetic unit called RCCX. We describe molecular studies on RCCX haplotypes revealing a unique recombination giving rise to a TNXB/TNXA hybrid gene, CYP21A deletion and CYP21B duplication on one chromosome of the propositus. His other chromosome carries a deletion of CYP21A-TNXA-RP2-C4B genes, resulting in the total absence of CYP21A genes and the presence of three CYP21B genes in the genome.

[Inborn deficiency of complement C4A and C4B isotypes in persons infected with Chlamydia]. / Vrozhdennye defitsity izotipov C4A i C4B komponenta C4 komplementa u lits, inifitsirovannykh khlamidiiami.

The difference in the functional activity of the isotypes A and B of component C4 of human complement was used to determine their ratio to detect the inherited deficiency of the isotypes. The frequency of deficiency in healthy persons blood donors was equal for C4A and C4B (0.14 for each isotype), i.e. 14% of total number (22) donors, or 28% totally. These results agree with the literary data, on which the frequency of deficiency of C4A is 0.14, and of C4B is 0.11-0.16. The inherent deficiencies of C4A and C4B for persons infected by Chlamydia were studied. For this purpose the patients (35 persons) with in blood antibodies (IgG or IgM) to Chlamydia (C. trachomatis, C. psittaci and C. pneumoniae) were investigated. The frequencies of deficiency of C4A and C4B were 0.29 and 0.46 respectively. Thus, the number of the undeficiency patients was only 25%, while among healthy persons 70-75% of individuals not having deficiencies of isotypes C4 were observed. The deficiencies of isotypes of C4 at this pathology is detected for the first time. The obtained data suggest the existence of the predisposition to the development of diseases stipulated by Chlamydia in persons with inherent deficiency of C4 component of complement.