HLA-DQ RFLP variants of five HLA-DQw2-bearing major histocompatability complex extended haplotypes

We have analyzed genomic DNA in a large number of independent examples of five HLA-DQw2-bearing extended haplotypes for their associated subtypes by restriction fragment length polymorphism (RFLP) using DRB, DQA, and DQB probes after Taq I and Pst I digestion and Southern blotting. In addition to three previously described HLA-DQw2 subtypes, DQw2a, DQw2b, and DQw2c, we observed a fourth subtype, HLA-DQw2d, characterized by 5.8 kilobase (kb) DRB/Taq I, 2.4, 2.3, and 1.8 kb DQB/Taq I, and 8.0 and 2.3 kb DQA/Pst I fragments. All 22 independent examples of the extended haplotype [HLA-B8,SCO1,DR3] carried DQw2a and all 11 independent examples of [HLA-B18,F1C30,DR3] carried DQw2b. In addition, all independent examples (21 and 4, respectively) of two DR7-carrying extended haplotypes, [HLA-B44,FC31,DR7] and [HLA-Bw47,FC91,0,DR7], carried DQw2c and all independent examples of [HLA-Bw57,SC61,DR7] carried DQw2d. Our results show that the DNA in the DR/DQ region of extended haplotypes is relatively fixed and that different DQw2 subtypes characterize different DQw2-bearing extended haplotypes.     

Complotype genetic loci segregate more frequently with HLA-DR than with HLA-B

The loci for BF, C2, C4A, and C4B are very closely linked to each other so that alleles of these plasma protein markers occur in populations in linkage disequilibrium and are inherited as single genetic units called complotypes. These complotypes are coded by a DNA region of the short arm of chromosome 6 embracing approximately 100 kilobases, which serve as a marker of the major histocompatibility complex. We have studied the complotypes of nine families with known HLA-B/DR crossovers. In seven families, the complotypes were inherited with HLA-DR, including in one family with a double recombination. The haplotype HLA-A28, Cw1, B27, FC3, 20, DR4 of JTr resulted from two recombinations between HLA-A2, Cwl, B27, SC42, DR7 and HLA-A28, Cwx or Cw1, B37, FC3, 20, DR4. In the remaining two families (Ro and Lo) the complotypes were inherited with HLA-B. The haplotype A2, Cw5, Bw44, SC30, DR3 of StLo resulted from paternal recombination between the haplotypes A2, Cw5, Bw44, SC30, DR4 and A24, B8, SC01, DR3, and the haplotype A24, Cw4, Bw35, SC31, DR3 of NaRo resulted from maternal recombination between A24, Cw4, Bw35, SC31, DR4 and A26, Bw41, FC31, DR3. Our data suggest that the complotype region maps closer to HLA-D than to HLA-B.     

Quantitative variation of C4 variant proteins associated with many MHC haplotypes

C4 protein variants were analyzed in 64 individuals, of which 51 were either homozygous or heterozygous for an extended major histocompatibility complex (MHC) haplotype (a fixed combination of MHC alleles). The relative amount of each C4 variant was measured by densitometric scanning of stained immunofixed electrophoretic patterns of neuraminidase- and carboxypeptidase-treated samples. The relative concentrations of C4 variants on any haplotype were stable and inherited in families. In five of the eight extended haplotypes investigated, the amount of one of the C4 variants relative to others in the same pattern was increased:[HLA-B8, SC01, DR3] and[HLA-B7, SC31, DR2] produced an approximately doubled amount of C4B1;[HLA-B18, S042, DR2] an increased amount of C4B2; and[HLA-B44, SC30, DR4] a double amount of C4A3. The extended haplotype[HLA-Bw57, SC61, DR7] gave rise to two to three times as much C4B1 as C4A6. In the extended haplotypes[HLA-B44, FC31, DR7] and[HLA-Bw62, SC33, DR4], the results did not clearly indicate differences in expression of the C4 isotypes. DNA analysis possibly supported an actual gene duplication only for the haplotype[HLA-B7, SC31, DR2]. The results suggest that, in addition to variation in the number of structural genes, other MHC-linked mechanisms may be involved in the regulation of the relative amounts of C4A or C4B protein specified by any haplotype.     

Novel detection of restriction fragment length polymorphisms in the human major histocompatibility complex

Cosmid genomic DNA clones have been used as hybridization probes in genomic Southern blot analysis to define restriction fragment length polymorphisms (RFLPs) in the major histocompatibility complex (MHC). Using 14 different enzymes and three overlapping cosmid clones we have detected six RFLPs in a 100 kilobase (kb) segment of DNA in the class III region extending centromeric of theTNFA gene towardHLA-DR. Four of the five RFLPs, defined using the enzymesTaqI,Rsa I,Hinc II, andHind III, and detected by the cosmid clone cosM7B, map to a 29 kb segment of DNA that includes all of the recently described G2 (BAT2) gene and a large portion of the 3 end of the G3 (BAT3) gene. The different RFLP variants were established by analyzing the DNA from three informative families and a panel of 51HLA-homozygous typing cell lines. CosM7B detectsTaq I variants of 4.3 kb, and 2.9 kb or 2.8 kb, Rsa I variants of 2.9 kb or 2.4 kb,Hinc II variants of 5.8 kb or 3.8 kb and 1.4 kb, and aHind III variant of 4.8 kb, while cosOT2 detects Taq I variants of 4.5 kb or 4 kb. The distribution of theRsa 1, Hinc II and Taq I RFLPs detected by cosM7B, and theTaq I RFLP detected with cosOT2, within the panel of cell line DNAs was assessed by Southern blotting. The 4.3 kbTaq I variant was observed in only one cell line with the extended haplotypeHLA-A29, C-, B44, SC30, DR4. The other RFLPs, however, occurred much more frequently. The 2.8 kb Taq I variant was observed in 20 % of haplotypes, the 2.9 kbRsa I variant was observed in 42% of haplotypes, and the 5.8 kbHinc I variant was observed in 12 % of haplotypes analyzed. The 4.5 kbTaq I variant detected by the overlapping cosmid cosOT2 was present in 21 % of haplotypes. Analysis of the RFLP variants with each other revealed seven different haplotypic combinations. Three of the haplotypic combinations were each subdivided into two subsets on the basis of the Nco I RFLP variant they carried at theTNF-B locus. These haplotypic combinations potentially allow differentiation among different extended haplotypes such asHLA-B8, SC01, DR3, HLA-B18, F1 C30, DR3, andHLA-B44, FC31, DR7. The RFLPs detected by the cosmid clones thus provide new tools which will be useful in the further genetic analysis of the MHC class III region.     

Identification of HLA-B44 subtypes associated with extended MHC haplotypes

The HLA class I antigen B44 is found in each of two different extended major histocompatibility haplotypes (allele combinations of HLA-B, HLA-DR, and complement genes BF, C2, C4A, and C4B in linkage disequilibrium). Using isoelectric focusing, two variants of HLA-B44 were identified. The basic variant was found in all cell lines with the extended haplotype HLA-B44, DR7, FC31, and the acidic variant in all cell lines with the extended haplotype HLA-B44, DR4, SC30. The occurrence of each antigen variant with a unique extended haplotype explains previous observations concerning the nonrandom association of B44 variants with DR antigens.     

Sharing of MHC haplotypes among apparently unrelated patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency

From the study of HLA, complement, and glyoxalase I alleles in 82 Venezuelan individuals belonging to 19 families of mixed ethnic origin having 20 affected newborns with salt-wasting congenital adrenal hyperplasia due to 21-hydroxylase (21-OH) deficiency, a total of 38 disease haplotypes and 53 nondisease haplotypes were found. Of the pathological haplotypes 47 % were found to share the HLA-B39 or -Bw62 specificities, 55 % of them in combination with the BFS, C2C, C4A4, C4B2 (SC42) complotype. The frequencies of HLA-B39 and -Bw62 among the affected haplotypes were 29 and 18% as compared with 6 and 0 % among the nondisease haplotypes of the same families. Statistical associations (P < 0.01) with salt-wasting adrenal hyperplasia were found with the SC42 complotype and with the combination SC42, HLA-B39. These results are markedly different from those reported in the literature which show an association at the population level among many Caucasoid samples of HLA-Bw47 and the extended haplotype (HLA-Bw47, DR7, FC91, 0) with the salt-wasting form of the disease. Furthermore, four of the unrelated patients reported here were homozygous for all the major histocompatibility complex loci tested, while three others were homozygous for at least two HLA loci. Analysis of the geographical origin of the grandparents indicated clustering of the deficiency carrier HLA haplotypes. This observation, together with the fact that there is an excess of homozygotes among the patients in Venezuela, strongly suggests that salt-wasting 21-OH deficiency congenital adrenal hyperplasia is mostly the result of a founder effect of relatively few independent mutations and, thus, of identity by descent of a few abnormal alleles at the 21-OHB locus in most cases. The mutation marked by HLA-Bw47 was not observed in this population.     

HLA-DR2, [HLA-B7, SC31, DR2], and [HLA-B8, SC01, DR3] haplotypes distinguish subjects with asthma from those with rhinitis only in ragweed pollen allergy.

MHC haplotypes were determined for 52 patients with ragweed pollen allergy, with and without asthma, and 27 non-atopic controls. Total IgE levels were unimodally distributed in all study groups and were higher in atopic patients in general compared with non-atopics. There was no difference in total IgE levels in patients with rhinitis only compared with those with rhinitis and asthma. IgE anti-Amb a V was detected (after subtraction of values representing the means + 2 SD of the non-atopics) in 9 of 20 asthmatics but only 3 of 32 patients with only rhinitis and was thus associated with asthma. Mean anti-Amb a V was much higher in the antibody-positive asthmatics (1710 U/ml) than in the positive patients with rhinitis only (469 U/ml). The extended MHC haplotype [HLA-B7, SC31, DR2] and its possible DR-containing fragment (SC31, DR2), were found almost exclusively among the patients with IgE anti-Amb a V and were significantly elevated in patients with asthma. DR2 in general, but not DR2 without SC31, was significantly increased in frequency in patients with anti-Amb a V. In contrast, the extended haplotype [HLA-B8, SC01, DR3] and DR3 in general were increased among patients with rhinitis only and patients without IgE anti-Amb a V compared with general controls. Thus, [HLA-B8, SC01, DR3] and DR3 appear to be "protective" for the production of this antibody and the occurrence of asthma. The findings are consistent with an MHC-linked gene or genes on [HLA-B7, SC31, DR2] (but not necessarily DR2, Dw2, or DQw6 in general) controlling the IgE immune response to Amb a V and associated with asthma in ragweed pollen-sensitive subjects. In patients with rhinitis alone and generally undetectable levels of IgE anti-Amb a V, the increase in [HLA-B8, SC01, DR3] and DR3 may mark a response to an as yet unidentified Ag associated with ragweed allergy and rhinitis only.     

C4 allotyping distinguishes HLA-1314.1 and B14.2 subgroups

Complement allotyping (C4, C2, and BF) was performed in 60 unrelated individuals and 15 families characterized for the subtypes (14.1 and 14.2) within HLA-B14. Eighty-seven percent of B14.2 individuals typed positive for the rare C4A2 variant. In contrast, less than 7% of B14.1 individuals were positive for this C4 allotype which is in keeping with a control background frequency. Family studies revealed that three distinct complotypes (complement haplotypes) are characteristic for the two HLA-1314 subgroups. The SC22 and FC31 complotypes characterize the B14.2 subtype, whereas SC31 appears to define B14.1.     

Complotypes in individuals of African origin: frequencies and possible extended MHC haplotypes

We analyzed the frequency distribution of 106 complotypes [four allele sets of the major histocompatibility complex (MHC) genes for the complement proteins factor B, C2, C4A, and C4B] from 32 Black families residing in Boston and Washington, DC. Twenty-five different complotypes were identified, among which there were four complotypes that had not been previously observed in our large database of complotypes compiled from family studies of Boston Caucasians and that are, presumably, unique to individuals of African origin. These four African-derived complotypes areFC(1,90)0, FC63, S1C2,17, andSC(3,2,90)0. The frequencies of two of these four unique Black complotypes,FC(1,90)0 andFC63, were increased significantly when compared to Caucasians (p_corr <0.00042, p_corr=0.00294, respectively). The complotypeFC(1,90)0 was in positive linkage disequilibrium withHLA-DR3 haplotypes containing theB locus antigens Bw42, Bw52, Bw53, and Bw58, whileFC63 was associated withHLA-Bw70,-DR5. These findings demonstrate the extensive polymorphism of complotypes in Blacks, and also suggest that it may be possible to define unique extended haplotypes of African origin.     

Ancestral haplotypes reveal the role of the central MHC in the immunogenetics of IDDM

The major histocompatibility complex (MHC) contains multiple and diverse genes which may be relevant to the induction adn regulation of autoimmune responses in insulin dependent diabetes mellitus (IDDM). In addition to HLA class I and II, the possible candidates include TNF, C4, and several other poorly defined polymorphic genes in the central MHC region. This study describes two approaches which take advantage of the fact that the relevant genes are carried by highly conserved ancestral haplotypes such as 8.1 (HLA-B8, TNFS, C4AQO, C4B1, DR3, DQ2). First, three diabetogenic haplotypes (two Caucasoid and one Mongoloid) have been compared and it has been shown that all three share a rare allele of BAT3 as well as sharing DR3, DQ2. In 43 sequential patients with IDDM the cross product ration for BAT3S was 4.8 (p<0.01) and 6.9 for HLA-B8 plus BAT3S (p<0.001). Second, partial or recombinant ancestral haplotypes with either HLA class I (HLA-B8) or II (HLA-DR3, DQ2) alleles were identified. Third, using haplotypic polymorphisms such as the one in BAT3, we have shown that all the patients carrying recombinants of the 8.1 ancestral haplotype share the central region adjacent to HLA-B. These findings suggest that both HLA and non-HLA genes are involved in conferring susceptibility to IDDM, and that the region between HLA-B and BAT3 contains some of the relevant genes. By contrast, similar approaches suggest that protective genes map to the HLA class II region.     

Localization of C4 genes within the HLA complex by molecular genotyping

Segregation of the complement component, C4, was analyzed in six families that each included an individual who inherited an HLA haplotype where a crossover event had occurred in the region between HLA-B and HLA-DR. Two cDNA clones corresponding to the C4 gene were utilized as probes in Southern blot analysis of DNA from members of each family. Restriction fragment length polymorphisms (RFLP) were observed and were assigned to haplotypes. In one family RFLP, hybridizing with the C4 probes, segregrated with HLA-B, and in four families RFLP segregated with HLA-DR; one family was not informative in this respect. These analyses have made it possible to localize the genes for C4 between HLA-B and HLA-DR by molecular genotyping and to characterize three different genomic configurations of C4 genes by limited restriction mapping.Abbreviations RFLP restriction fragment length polymorphisms - LCL lymphoblastoid cell lines     

Order of class III genes relative to HLA genes determined by the haplotype method

The B18 C4A3 C4BQ0 BfF1 DR3 haplotype was found to be ideal for determining the order of C4 and Bf relative to HLA-B and DR by the haplotype method. All the copies of this haplotype are assumed to be derived from a single ancestral haplotype. Sixteen of the twenty-six BfFl-containing haplotypes carried all of the alleles from this ancestral haplotype. Most of the other BfFl-containing haplotypes could be derived from the ancestral haplotype by a single crossover event for one of the two possible gene orders. This suggests that B18 C4A3 C4BQ0 BfFl DR3 is the sole source of the BfFl allele. The uncommon C4 type on B18 C4A3 C4BQ0 BfFl DR3 facilitates recognition of the BfFl-containing products of recombination between Bf and C4. One such recombinant haplotype was found which shows that the orientation of the class III genes is as follows: C4 is closest to HLA-B and Bf is closest to HLA-DR. This gene order is supported by all the earlier unequivocal results obtained using the haplotype method (Olaisen et al. 1983, Marshall et al. 1984a). Combining these results with the information on class III genes obtained from overlapping cosmid clones (Carroll et al. 1984) and earlier mapping studies (Robson and Lamm 1984) shows that HLA-B is telomeric to 21B. C4B, 21A, C4A, Bf and C2 then follow 21B in that order covering 120 kb. HLA-DR is located further toward the centromere.     

Linkage disequilibrium of HLA-SB1 with the HLA-A1, B8, DR3, SCO1 and of HLA-SB4 with the HLA-A26, Bw38, Dw10, DR4, SC21 extended haplotypes

Homozygous typing cells from 13 normal HLA-A1, B8, Dw3, DR3 and five normal HLA-A26, Bw38, Dw10, DR4 individuals were typed for the following markers: HLA-SB, MB, MT; complement proteins BF, C2, C4A, C4B; and GLO. Ninety-one percent of A1, B8, Dw3, DR3 homozygous individuals (HI) tested were homozygous for BF ^* S, C2 ^* C, C4A ^* QO, and C4B ^*1 (SCO1 complotype), which indicates that the SCO1 complotype is in linkage disequilibrium with the A1, B8, DR3 haplotype in randomly selected normal populations. Sixty-seven percent of HLA-A1, B8, Dw3, DR3, SCO1 positive HI also expressed SB1; since the frequency of SB 1 in random Caucasian populations is 11.2%, this finding indicates that SB1 is in linkage disequilibrium with the A1, B8, DR3, SCO1 extended haplotype. All HI with the A26, Bw38, Dw10, DR4 haplotype were homozygous for both SC21 and SB4, suggesting that SC21 and SB4 should be included in the A26, Bw38, Dw10, DR4 extended haplotype. On the other hand, neither of the GLO markers were found in association with either haplotype. The results of this study indicate that HLA-SB is included in some extended haplotypes and may be important in these markers for diseases such as insulin-dependent diabetes mellitus. This study also demonstrated an apparent influence of HLA-SB on primary mixed lymphocyte culture (MLC) responses. The mean relative response of primary MLCs between individuals matched for HLA-A, B, D, DR, MB and MT but not SB was 40% of that for the MLCs with mismatched HLA-D, significantly higher than the MLCs matched for all HLA and complotypes.     

CYP21/C4 gene organisation in Italian 21-hydroxylase deficiency families

Summary A total of 33 Italian 21-hydroxylase (21-OH) deficiency families were investigated using a combination of short and long range restriction mapping of the CYP21/C4 gene cluster. The analyses revealed that large-scale length polymorphism in this gene cluster strictly conformed to a compound variable number of tandem repeats (VNTR) plus insertion system with between one and four CYP21 + C4 units and seven BssHII restriction fragment length polymorphisms (RFLPs) (75kb, 80kb, 105kb, 110kb, 135kb, 140kb and 180kb). A total of 9/66 disease haplotypes, but only 1/61 nondisease haplotypes, showed evidence of gene addition by exhibiting three or more CYP21 + C4 repeat units. Of these, two were identified in one 21-OH deficiency patient who has a total of eight CYP21 + C4 units, being homozygous for the HLA haplotype DR2 DQ2 B5 A28. This haplotype carries four CYP21 + C4 units, three of which contain CYP21A-like genes and one of which contains a CYP21B-like gene that presumably carries a pathological point mutation. Of the other gene addition haplotypes associated with 21-OH deficiency, four show three CYP21 + C4 units flanked by HLA-DR1 and HLA-B14 markers. Although such haplotypes have commonly been associated with non-classical 21-OH deficiency, three examples in the present study are unexpectedly found in two salt-wasting patients, who are respectively homozygous or heterozygous for this haplotype. Only 7/66 disease haplotypes showed evidence of a CYP21B gene deletion.     

Genetic heterogeneity of insulin-dependent (type I) diabetes mellitus: evidence from a study of extended haplotypes

Two hundred subjects with insulin-dependent (type I) diabetes mellitus (IDDM) were typed for HLA-B, HLA-DR, and properdin factor B (Bf). HLA and Bf antigen and haplotype frequencies in subjects were compared with control frequencies derived from the 8th HLA Workshop. Frequencies of extended haplotypes (defined by B-Bf-DR alleles on a chromosome) were also contrasted with control frequencies. Significant positive associations between IDDM and HLA-B8, DR3, DR4, BfS, and BfF1 were confirmed, as were significant negative associations between IDDM and HLA-B7, DR2, DR5, DR7, and BfF. One haplotype (B7-BfS-DR2) exhibited significant negative association, while five haplotypes (B8-BfS-DR3, B8-BfS-DR4, B15-BfS-DR4, B18-BfF1-DR3, and B40-BfS-DR4) exhibited significant positive associations with IDDM. In this sample, 64% of all probands carried at least one of the high-risk haplotypes. In conclusion, the occurrence of five "high-risk" haplotypes associated with IDDM provides evidence for previously undocumented genetic heterogeneity and suggests that possibly more than two HLA-region genes may be involved in IDDM susceptibility.     

Polymorphisms of DQ β genes in HLA-DR4 haplotypes from healthy and diabetic individuals

The restriction fragment length polymorphism (RFLP) of DQ was assessed in a panel of control and insulin-dependent diabetes (IDD) patients who were serologically typed as HLA-DR4 homozygotes or HLA-DR3, DR4 heterozygotes. Digestions of genomic DNA with Barn HI, Bg1 II, Pst I, Xba I, and Hind III revealed a total of 15 RFLPs in the panel of 71 HLA-DR4 chromosomes. These RFLPs were organized into six allelic groups on the basis of segregation analysis in families. Complete RFLP haplotypes for the 5 restriction enzymes could be constructed for 42 of the HLA-DR4 chromosomes. This analysis revealed 18 RFLP haplotypes of DQ associated with the DR4 chromosomes tested. Two of these haplotypes, designated DQ3.DR4.a and DQ3.DR4.b, accounted for over 50 % of the DR4 chromosomes analyzed. These two haplotypes were antithetical for the RFLPs detected by all five enzymes, indicating that they represent very distinct forms of DQ . The remaining 16 haplotypes were infrequent or unique and were closely related to either a DQ3.DR4.a or DQ3.DR4.b. Two of the RFLPs detected, a 5.8 kb Bg1 II fragment and a 10.5 kb Barn HI fragment, had increased frequencies in disease-associated chromosomes. However, none of the RFLPs we detected exhibited a statistically significant increase in IDD or control populations. In contrast, the DQ3.DR4.b DQ haplotype was significantly decreased in IDD-associated DR4 chromosomes. (P=0.04). These results suggest that the DQ3.DR4.b DQ allele may be protective for the development of IDD.     

The distribution of polymorphic Alu insertions within the MHC class I HLA-B7 and HLA-B57 haplotypes

There are five polymorphic Alu insertion (POALIN) loci within the major histocompatibility complex (MHC) class I region that have been strongly associated with HLA class I alleles, such as HLA-A1, HLA-A2 and HLA-B57. In order to assess the variability and frequency of POALIN distribution within two common HLA-B haplotypes, we detected the presence of the MHC class I POALIN by PCR in a panel of 15 individuals with HLA-B57 and 47 homozygous individuals with 7.1 AH (HLA-B7, -Cw7, -A3) obtained from the Australian Bone Marrow Donor Registry, and also from four families (25 individuals) containing the HLA-B57 allele. Only two of the 47 HLA-B7 genotypes had a detectable POALIN, whereas all of the HLA-B57 genotypes had at least one or more POALINs present, confirming that certain MHC class I haplotypes are relatively POALIN-free and others are POALIN-enriched. Six distinct HLA-B57 haplotypes, based on differences at the HLA-A locus and three of five POALIN loci, were identified that appear to have evolved by different mechanisms, including either by shuffling different combinations of conserved alpha and beta blocks or by recombination events involving two or more previously generated HLA-B57 haplotypes.     

Molecular analysis distinguishes two HLA-DR3-bearing major histocompatibility complex extended haplotypes

We detected restriction fragment length polymorphisms that distinguish the extended haplotype HLA-B8,DR3,SCO1 from HLA-B18,DR3,F1C30 at the DR beta and DQ beta loci with five of seven restriction endonucleases used. One set of restriction fragments was always found on HLA-B8,DR3,SCO1 and associated with DRw52a, while the other was present on HLA-B18, DR3,F1C30 and correlated with DRw52b (the gene encoding the subtype of DRw52 associated with the BO1 or LB-Q1 antigen). Furthermore, using a full-length DQ beta gene probe, we found division in the DQw2 haplotype, in which DQw2a always associated with HLA-B8, DR3,SCO1, while DQw2b always occurred with HLA-B18,DR3,F1C3O. Our evidence thus indicates that serologically defined HLA-DR3, HLA-DRw52, and HLA-DQw2 are each produced by two structurally very different sets of genes, one set occurring in HLA-B8, DR3,SCO1, and the other in HLA-B18,DR3,F1C30.Abbreviations used in this paper BSA bovine serum albumin - MHC major histocompatibility complex - EDTA ethylenediaminetetraacetic acid - SDS sodium dodecyl sulfate     

Possible association of the exetended MHC haplotype B44-SC30-DR4 with autism

We previously reported that the complement C4B null allele appears to be associated with infantile autism. Since the C4B null allele is known to be part of the extended or ancestral haplotype [B44-SC30-Dr4], we investigated the incidence of [B44-Sc30-DR4] in 21 autistic children and their parents. This extended haplotype was increased by almost six-fold in the autistic subjects as compared with healthy controls. Moreover, the total number of extended haplotypes expressed on chromosomes of autistic subjects was significantly increased as compared with those expressed on chromosomes of healthy subjects. We conclude that a gene related to, or included in, the extended major histocompatibility complex may be associated with autism.     

The structure ofHLA-B35 suggests that it is derived fromHLA-Bw58 by two genetic mechanisms

The primary structure ofHLA-B51 andHLA-Bw52 suggested thatHLA-B51 was derived fromHLA-Bw52 by the combination of a genetic exchange withHLA-B8 and a point mutation. To investigate the evolution of theHLA-B5 cross reactive group, theHLA-B35 gene was cloned and the primary structure was determined.HLA-B35 is identical toHLA-Bw58 except in the α₁ domain. The α₁ domain ofHLA-B35 except Bw4/Bw6-associated amino acids is identical to that ofHLA-B51 ^*, which was suspected to be an intermediate gene betweenHLA-B51 andHLA-Bw52. These data suggest thatHLA-B35 has evolved fromHLA-Bw58 in two steps; an in vivo replacement of the α₁ domain withHLA-B51 and genetic exchange with one of theHLA-Bw6 genes. These three genes andHLA-Bw58 are postulated to share a common ancestor.