CONSERVATION OF ANCESTRAL HAPLOTYPES TELOMERIC OF HLA-A

Genes that predispose to haemochromatosis are thought to be located within the several megabases telomeric of HLA-A. Further recombinant mapping has been used previously to map susceptibility genes for diseases such as insulin-dependent diabetes mellitus, myasthenia gravis and cystic fibrosis, and should be useful in relation to haemochromatosis. However, this method requires the recognition of ancestral haplotypes within the susceptibility region. Using a panel of six microsatellite markers from this region (MOG A, MOG B, MOG C, D6S464, D6S306 and D6S105), we show that ancestral haplotypes extend telomeric of HLA-A, at least as far as D6S105. Nine of 14 haplotypes carrying HLA-B7 and HLA-A3 shared the same microsatellite alleles between HLA-A and at least D6S105. Similarly, nine of 10 haplotypes sharing HLA-B8 and HLA-A1 shared the same microsatellite alleles, although a different set to those with HLA-B7 and HLA-A3. Haplotypes representing historical recombination events were also identified. These two findings demonstrate that recombinant mapping may be applicable to the mapping of disease genes in this region.     

Complement C4A, C4B and BF haplotypes in Koreans

Specific alleles at C4A, C4B and BF loci occur in populations and are inherited in complotypes, which are linked with particular HLA haplotypes. Considerable differences in complement allele and complotype frequencies have been observed among various ethnic groups. In the present study, 109 Korean families were analyzed for complement and complotype polymorphism. Thirty-four different complotypes were detected: the most common was BF*S-C4A*3-C4B*1 (S31) with a frequency of 42.2%, followed by S42 (14.3%) and F31 (13.8%). Three complotypes, S42, F31, and FQ01, showed positive linkage disequilibrium. Some of the complotypes were linked with characteristic HLA haplotypes. Two complotypes carrying duplicated C4A genes, S3+31 (BF*S-C4A*3-C4A*3-C4B*1) and S3+2Q0(BF*S-C4A*3-C4A*2-C4B*Q0), were exclusively associated with HLA-A24-Cw7-B7-DR1-DQ1 and A24-CBL-B52-DR15-DQ1 haplotypes, respectively. Twelve families showed recombinant haplotypes, nine in the class I region, three between the HLA-B and HLA-DR loci, and none in the class III region. Maternal recombination occurred twice as frequently as paternal. The results obtained in this study represent the frequencies of complotypes and extended HLA haplotypes of well-defined Koreans, based on a family study.     

HLA-A region in highly sensitized patients: another immune response gene region.

HLA haplotypes were assigned by family typing in 94 prospective kidney transplant recipients. An HLA-A region of the HLA-A, B, DR haplotypes was found in association with high levels of antibodies against lymphocytes. There was a significant difference in the frequency of HLA-B8-positive haplotypes among the patients with regard to the distribution of HLA-A alleles (p = 0.0028); on the same haplotype the A1 and B8 alleles were found in moderately and weakly sensitized patients and HLA-A alleles other than A1 were present with B8 in highly sensitized patients. A significantly higher number of highly sensitized patients when compared with moderately sensitized patients had haplotypes with HLA-A alleles in negative linkage disequilibrium with HLA-B alleles (77 vs. 10%, p = 0.014). The results are in good agreement with a previous suggestion that the interaction between the HLA-A class I and class II regions regulates the immune response. Determination of HLA haplotypes might identify patients at high risk for broad and persisting sensitization.     

LINKAGE RELATIONSHIPS OF THE LOCI OF THE MAJOR HISTOCOMPATIBILITY COMPLEX IN FAMILIES WITH A RECOMBINATION IN THE HLA REGION

A number of families with an established recombination in the major histo-compatibility complex has been investigated for markers known to be coded by genes of this linkage group. The results provide further data on the relative position of the loci for HLA-A, HLA-B, HLA-C, HLA-D, Bf, Chido, Rodgers and PGM₃ on chromosome 6. A positive lodscore for linkage between HLA and blood group P was found; lodscores between HLA and nineteen other markers were negative.     

Intra-HLA recombinations localizing the 21-hydroxylase deficiency gene within the HLA complex

Close linkage between HLA and the gene for 21-OH deficiency causing congenital virilizing adrenal hyperplasia (CVAH) has been well documented. HLA-A/B and HLA/GLO recombination data placed the CVAH gene within the HLA-A to GLO interval, with CVAH invariably segregating with HLA. HLA-A,B,C,DR and GLO typing and ACTH stimulation to determine carrier status was done on seven families. Carrier status correlated with the appropriate HLA haplotypes in all offspring, with two exceptions. Two intra-HLA recombinants were detected in one three-generation family. The father of the proband is homozygous for HLA-A2,Cw2,B27 but is a DR2/DR4 heterozygote. The CVAH gene segregated with DR2 in all but one of his offspring who is a carrier and is DR4. This finding is consistent with recombination between the CVAH gene and DR. Study of the father's family confirmed synteny of the CVAH gene and DR2. Three of four sibs of the father inherited this haplotype and were CVAH carrier, as was the paternal grandmother, whose other haplotype was A1, Bw44,DR1. One of the father's sibs was shown serologically to be a HLA-B/D maternal recombinant and a noncarrier. she inherited the A1,Bw44 of one maternal haplotype, but the DR2 of the other. In both recombinants in this family the CVAH gene segregated with the A to B interval, separate from D. While we cannot determine whether the CVAH gene is in the HLA-A to B or B to D interval, this is the first report of two intra-HLA recombinations in one family that unequivocally map the CVAH gene inside HLA-D.     

Molecular, serological and population studies of the alleles and products of HLA-B*41.

The HLA-B41 specificity was first identified over 25 years ago and, although both serological and biochemical studies have suggested its subdivision, it is only recently that two HLA-B*41 alleles (B*4101 and B*4102) have been identified and sequenced. We designed three oligonucleotide primers, combined in two mixtures to define these alleles by PCR using sequence-specific primers (PCR-SSP) in a random normal population of 9,464 HLA-A, B, DR, DQ typed Northern European Caucasoid donors from the Welsh Bone Marrow Donor Registry. The HLA-B41 phenotype frequency was 0.835%, and of the 79 HLA-B41 subjects 22 (27.85%) were B*4101 and 57 (72.15%) were B*4102. The phenotype frequencies of B*4101 and B*4102 were 0.232 and 0.602%, respectively, and the gene frequencies were 0.00116 and 0.00301, respectively. Formal two-locus linkage disequilibrium (LD) analysis demonstrated significant associations between B*4101 and A30 and DR11, and between B*4102 and A66 and DR13. LD analysis of three loci showed significant associations between B*4101, DR7, DQ2 and B*4101, DR11, DQ7 (DQB1*0301/0304) and between HLA-A3, B*4102, DR13; A66, B*4102, DR7; A66, B*4102, DR13; B*4102, DR13, DQ6 and B*4102, DR13, DQ7. Examination of the HLA phenotypes (including HLA-C) of the B*41 subjects, together with the LD analysis findings, suggested four different HLA haplotypes bearing B*4101 and five B*4102 haplotypes. The most frequent B*4101 haplotype was: HLA- A30 or other A allele, Cw*1701, B*4101, DRB1*1102, DQB1*0301 and the most freqent B*4102 haplotype was: A*6601 or A3 or other A allele, Cw*1701, B*4102, DRB1*1303, DQB1*0301. In addition, the well-known association of A66 with B41 was between A*6601 and B*4102, and although both B*41 alleles were commonly in association with Cw*1701, B*4101 was found with Cw*07. One-dimensional isoelectric focusing (1D-IEF) analysis of HLA-B proteins from 2 B*4101 and 2 B*4102 subjects clearly showed that the B41.1 and B41.2 1D-IEF variants, identified in the 10th International Histocompatibility Workshop, corresponded to B*4101 and B*4102 products, respectively. Serological titration studies, with 59 lymphocytotoxic pregnancy antisera, containing an HLA-B41 component and stimulated by up to five different HLA-B specificities, were unable to differentiate the two groups of B*41 subjects. This suggests that partition of the HLA-B41 specificity will not normally be achieved by classical serological methods. It is suggested that the previous alleged serological subdivision of HLA-B41 was founded on the unwitting use of antisera detecting the HLA-Cw*17 products.     

Polymorphism of HLA-A, -B, -DRB1, -DQA1 and -DQB1 haplotypes in a Croatian population.

We describe for the first time extended haplotypes in a Croatian population. The present study gives the HLA-A, -B, -DRB1, -DQA1 and -DQB1 allele and haplotype frequencies in 105 families with at least two offspring. All individuals were studied by conventional serology for HLA class I antigens (A and B), while class II alleles (DRB1, DQA1, DQB1) were typed using the PCR-SSOP method. HLA genotyping was performed by segregation in all 105 families. For extended haplotype analysis, 420 independent parental haplotypes were included. Fourteen HLA-A, 18 HLA-B, 28 DRB1, 9 DQA1 and 11 DQB1 alleles were found in the studied population. Most of the DRB1 alleles in our population had an exclusive association with one specific DQA1-DQB1 combination. This strong linkage disequilibrium within the HLA class II region is often extended to the HLA-B locus. A total of 10 HLA-A, -B, -DRB1, -DQA1, -DQB1 haplotypes were observed with a frequency 相似文献   

Extended HLA haplotypes in families with insulin-dependent diabetes mellitus in Northern Finland

Haplotypes including HLA, Bf and C4 loci were analyzed in a material comprising 55 families with diabetic children. One hundred and ten haplotypes found in IDDM patients were compared with 101 haplotypes present only in healthy family members. Two complotypes, BfSC4A3B3 and SC4A0B1 . were significantly more common (P <0.05) in the diabetic haplotypes, and these were in most cases found in haplotypic combinations with HLA-B15,Dw4,DR4 and HLA-B8.Dw3,DR3 genes, respectively. The B8/DR3 haplotype was better conserved, as 72% included the BfSC4A0B1 complotype as compared with only 35% of the B15/DR4 haplotypes with "high risk" C4A3B3 complement alleles (p <0.05). DR3 was found in 26% of the diabetic haplotypes and DR4 in 43%. DR4 associated with the Dw4 in 69% of cases and with D w14 in 26% of the diabetic haplotypes. Our results confirm that the two phenotypes found earlier to be associated with IDDM in Northern Finland, e.g. "B15, BfS, C4A3B3, Dw4, DR4" and "B8, BfS, C4A0B1, Dw3, DR3" are inherited as haplotypes.     

HSP70-Hom NcoI POLYMORPHISM AND HLA-ASSOCIATIONS IN THE FINNISH POPULATION AND IN PATIENTS WITH ANKYLOSING SPONDYLITIS OR REACTIVE ARTHRITIS

The NcoI polymorphism of the HSP70-Hom gene was investigated in the Finnish population and in two HLA-B27-associated autoimmune diseases. The two HSP70-Hom alleles were shown to be strongly associated to some specific HLA-B/DR haplotypes in random Finnish population and the segregation of the alleles as a part of these haplotypes was confirmed in 18 families. In addition, the HSP70-Hom alleles of 31 patients with ankylosing spondylitis (AS) and 38 with reactive arthritis (ReA) were compared with each other and with 56 unrelated healthy HLA-B27 positive individuals. The results indicated that the HSP70-Hom polymorphic variation is not connected independently to the different pathogenesis of AS and ReA, as no statistically significant differences between the patient groups and/or controls could be found. The HSP70-Hom status was investigated also in 28 homozygous HLA typing cells and when compared with previously published results of HSP70-1 and HSP0-2 polymorphisms, it appeared that these three MHC Class-III linked HSP70 genes segregated in fixed allelic combinations.     

HLA-Cw alleles associated with HLA extended haplotypes and C2 deficiency

Abstract: There are four MHC-linked complement genes, BF, C2, C4A and C4B, that are inherited as single DNA units, known as complotypes. Extended haplotypes were initially defined by studying the distribution of complotypes in relation to HLA-B and HLA-DR loci in Caucasian families. In order to analyze the distribution of HLA-Cw alleles in relation to extended haplotypes, we studied a large panel of MHC homozygous and heterozygous cell lines representing previously described Caucasian-derived extended haplotypes and 14 patients with complete C2 deficiency. HLA alleles were assigned using sequence-specific oligonucleotide probe hybridization (SSOP). Family analysis served to assign haplotypes for heterozygous samples. We found distinctive HLA-Cw alleles for each independent extended haplotype. Their association in each instance was statistically significant All patients with C2 deficiency carrying the haplotype [HLA-B18, S042, DR2] were associated with HLA-Cw*1203. These conserved allelic combinations may become an important tool for the study of human evolution and may contribute to the expeditious selection of prospective donors in clinical transplantation.     

Linkage disequilibrium in HLA cannot be explained by selective recombination

Abstract: Some combinations of HLA-A,-B and -DR antigens occur more frequently than would be expected from their gene frequencies in the population. This phenomenon, referred to as Linkage Disequilibrium (LD) has been the origin of many speculations. One hypothesis to explain LD is that some haplotypes are protected from recombination. A second hypothesis is that these HLA antigens preferentially recombine after cross-over, to create an LD haplotype. We tested these 2 hypotheses: from a pool of over 10,000 families typed in our department, we analyzed 126 families in which HLA-A:B or B:DR recombinant offspring was documented. To overcome a possible bias in our material, we used the non-recombined haplotypes from the same 126 families as a control group. Our results show that the number of cross-overs through LD haplotypes is not significantly lower then would be expected if recombination occurred randomly. Also the number of LD haplotypes created upon recombination was not significantly increased.     

HLA-A, -B and -DR allele and haplotype frequencies in Malays

One thousand four hundreds and forty-five Malays registered with the Malaysian Marrow Donor Registry were typed for HLA-A, HLA-B and HLA-DR. Fifteen HLA-A, twenty nine HLA-B and fourteen HLA-DR alleles were detected. The most common HLA-A alleles and their frequencies were HLA-A24 (0.35), HLA-A11 (0.21) and HLA-A2 (0.15). The most common HLA-B alleles were HLA-B15 (0.26), HLA-B35 (0.11) and HLA-B18 (0.10) while the most common HLA-DR alleles were HLA-DR15 (0.28), HLA-DR12 (0.27) and HLA-DR7 (0.10). A24-B15-DR12 (0.047), A24-B15-DR15 (0.03) and the A24-B35-DR12 (0.03) were the most frequent haplotypes. This data may be useful in determining the probability of finding a matched donor and for estimating the incidence of HLA associated diseases.     

Genetic mapping of the hemochromatosis locus on chromosome six

The purpose of this paper is to report a pedigree with hereditary hemochromatosis in which a recombination between the HLA-A and B loci occurred. Both the maternal and paternal HLA-A3, B7 haplotypes were carrying an allele for hemochromatosis. The A3, B12 haplotype of the proband was a recombinant of the maternal A3, B7 and A28, B12 haplotypes. The hemochromatosis locus segregated with the HLA-A locus and not with the HLA-B locus. Thus, the hemochromatosis locus maps in close proximity to the HLA-A locus.     

Complotypes, extended haplotypes, male segregation distortion, and disease markers

From our studies in Caucasian families of HLA, complement, and glyoxalase alleles have developed the concepts of the complotype and the extended haplotype. complotypes are clusters of the four genes for complement proteins encoded within the MHC designated (in arbitrary order) by their BF, C2, C4A, and C4B alleles. They are inherited in families and occur in populations as functionally single genetic units and exhibit linkage disequilibrium with HLA-B and HLA-DR alleles which are complotype, rather than complement gene allele, specific. In Caucasians, there are 10-12 common sets of HLA-B, DR, complotype sets that show significant linkage disequilibrium. These haplotypes constitute 25-30% of all MHC haplotypes in Caucasians. Because there is evidence for relative fixity of alleles on these chromosomes to an unknown extent beyond the HLA-B-DR interval, they have been called extended MHC haplotypes. It appears likely that it is these extended haplotypes that provide most of the known linkage disequilibrium pairs previously reported for MHC alleles as well as many of the known MHC allele-disease associations. The most common extended haplotype [HLA-B8, DR3, SC01], when it carries GLO2, is increased in type I diabetes mellitus and probably a number of other diseases, including gluten-sensitive enteropathy and membranoproliferative glomerulonephritis. In the families with these disorders studied by us, this haplotype exhibits male segregation distortion, a feature displayed by t-mutants found in wild mouse populations. This feature constitutes an important selective advantage for the chromosome and may contribute to the accumulation of susceptibility mutations for a variety of diseases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Allele frequencies and haplotypic associations defined by allelic DNA typing at HLA class I and class II loci in the Japanese population

HLA class I and class II allelic genotypes were determined in 371 unrelated individuals and 309 members of 81 families inhabiting the central Japan area. A total of 20 HLA-A alleles, 16 HLA-Cw alleles, 38 HLA-B alleles, 27 HLA-DRB1 alleles, 15 HLA-DQB1 alleles and 12 HLA-DPB1 alleles were detected. By the two-, three-, four-, five- and six-locus allelic association analyses extracted from the HLA-A to -DPB1 locus, 26 HLA-Cw-B haplotypes, 25 HLA-DRB1-DQB1 haplotypes, 42 HLA-Cw-B-DRB1 haplotypes, 37 HLA-Cw-B-DRB1-DQB1 haplotypes, 29 HLA-A-Cw-B-DRB1-DQB1 haplotypes and 21 HLA-A-Cw-B-DRB1-DQB1-DPB1 haplotypes with the frequencies of higher than 0.005 were recognized. Among 19 HLA-B alleles with the high allele frequencies (above 0.007), 9 HLA-B alleles, B*0702, B*1301, B*3701, B*3901, B*4006, B*4403, B*5201, B*5901 and B*6701 were found to be tightly associated with single HLA-Cw alleles. Most of HLA-DRB1 alleles showed strong associations with single HLA-DQB1 alleles, but DRB1*0802 and DRB1*1401 were associated with two different DQB1 alleles. Extended haplotypes carrying infrequent class I alleles with the allele frequencies of lower than 0.007 were defined by family studies. Gene frequencies and haplotypic associations within the entire HLA classical loci elucidated at the high resolution (four-digital) allelic level will provide useful information on anthropology, marrow donor registry, legal medicine and disease-association studies.     

Short tandem repeat (STR) haplotypes in HLA: an integrated 50-kb STR/linkage disequilibrium/gene map between the RING3 and HLA-B genes and identification of STR haplotype diversification in the class III region

We present a dense STR/linkage disequilibrium(LD)/gene map between the RING3 and HLA-B loci, reference allelic sizes on the most prevalent HLA haplotypes and their allelic frequencies in pedigree founders. This resource will facilitate LD, evolution and gene mapping studies, including comparisons of HLA and STR haplotypes and identification of HLA recombinants. The map was constructed by testing novel and previously reported STRs using a panel of 885 individuals in 211 families and 60 DNA samples from cell lines and bone marrow donors homozygous in the HLA-A, -B and -DR loci selected from over 15 000 entries into the registry of Swedish bone marrow donors. We have also analysed the variability of STR alleles/haplotypes on the most prevalent HLA haplotypes to identify STRs useful for fine mapping of disease genes in the region previously implicated in susceptibility to many disorders. The analysis of 40 HLA-A*01, B*0801, DRB1*03011, DQB1*0201 haplotypes in homozygous donors showed a surprising stability in 23 STRs between the class II recombination hot spot and HLA-B, with the average of 1.9% (16/838) variant alleles. However, 40% variant alleles were found at the D6S2670 locus in intron 19 of the tenascin-X gene both in the families and homozygous donors. The nucleotide sequence analysis of this STR showed a complex polymorphism consisting of tetra- (CTTT)(8-18) and penta-nucleotide (CTTTT)(1-2) repeats, separated by an intervening non-polymorphic sequence of 42 bp. The HLA-A1, B*0801, DRB1*03011, DQB1*0201 haplotypes had five (CTTT)(14-18)/(CTTTT)(2) variants with a predominant (CTTT)(16) allele, implicating the tetranucleotide component as the source of this ancestral haplotype diversification, which may be due to the location of D6S2670 in the region of the highest GC content in the human MHC.     

HLA Haplotype A33-B58-Cw10 May Modulate Radiographic Development of Bamboo Spine in Taiwanese Patients with Primary Ankylosing Spondylitis

Objective: To evaluate the possible relationship between HLA alleles and bony ankylosis of the spine (bamboo spine) in Taiwanese patients with ankylosing spondylitis (AS).Methods: A small cohort of HLA-B27 positive AS patients was conducted to analyze the effects of alleles and haplotypes on the development of bamboo spine. DNA typing of HLA class I and class II genes were performed by SSP method on primary ankylosing spondylitis patients with bamboo spine (n = 84) and spinal enthesopathy controls (n = 228). Odds ratios with 95% confidence intervals and P value were estimated. Determination of the most probable HLA haplotypes on all patients were constructed by comparison of the alleles carried by each patient with the HLA haplotype database established in Taiwanese population studies using homozygosity approach [1] and by expectation-maximum algorithm [2].Results: Allele frequencies of HLA A33, B58, Cw10, DR4, DR17 and DQ2 were significantly lower in bamboo patients as compared to non-bamboo controls. In contrast, allele frequencies of A24, B54, Cw15, DR11 and DR14 were significantly higher in bamboo patients. Less remarkably, high frequencies of B39, B51, Cw1 and Cw2 alleles were also noted in bamboo patients. Considering linkage disequilibria of alleles in haplotypes, HLA-A11-B27-Cw12 was the most common haplotype in both bamboo and non-bamboo groups (95.23% vs. 91.22%, respectively, P = 0.238). Haplotypes A33-B58-Cw10, A33-B58-Cw10-DR13 and A33-B58-Cw10-DR17 were significantly lower in bamboo patients as compared to those in controls (P < 0.001, P = 0.001, P = 0.002, respectively).Conclusion: Haplotypes A33-B58-Cw10, A33-B58-Cw10-DR13 and A33-B58-Cw10-DR17 showed a strong association with bamboo spine in Taiwanese AS patients. Detection of such haplotypes might be a great aid in the management of patients with the disease.     

HLA-A and HLA-B in Kenya,Africa: allele frequencies and identification of HLA-B*1567 and HLA-B*4426

HLA-A and HLA-B alleles of a population from Kenya, Africa were examined by sequencing exon 2 and exon 3 DNA and typing using a Taxonomy-based Sequence-analysis (TBSA) method. Extensive diversities were observed at both HLA-A and HLA-B loci in this population. Forty-one HLA-A alleles were identified from 159 unrelated individuals. The most frequently observed alleles were A*6802 (11.64%), A*02011/09 (9.75%), A*7401/02 (9.43%), A*3001 (7.86%), A*3002 (7.23%) and A*3601 (6.6%). Forty-nine HLA-B alleles were identified in 161 unrelated individuals, including two novel alleles, B*1567 and B*4426. The most frequently observed HLA-B alleles were B*5301 (9.01%), B*5801 (8.38%), B*4201 (7.76%), B*1503 (7.14%), B*1801 (6.21%), and B*5802 (5.90%). The most frequently observed HLA-A-B haplotypes were A*3601-B*5301 (3.55%) and A*3001-B*4201 (3.19%), followed by A*7401/02-B*5801 (2.84%), A*7401/02-B*5802 (2.84%) and A*02011/09-B*1503 (2.13%). Linkage disequilibrium and chi2 analysis showed the association of these HLA-A-B haplotypes at the antigen level to be significant. The frequencies of HLA-A and HLA-B alleles from the Kenyan population were compared with that of a population from Cameroon. The difference in allele and haplotype frequency distributions partly reflected the different ethnic composition of these two African populations.     

MOLECULAR ANALYSIS OF TWO RECOMBINANT MOUSE STRAINS WITH CROSSOVERS IN THE Eα RECOMBINATION HOT SPOT

Recombination in the E_α gene of the mouse major histocompatibility complex has been found to occur only in mice derived from crosses between strains with the k and p haplotypes. In the present paper the crossover sites of six additional strains were examined by RFLP analysis. These recombinant strains were derived from crosses between strains (B10.RPD1, B10.RPD2) with crossovers in the E_α gene and B10.M (H-2^f). Four have crossover sites between the E_α gene and the S region. One recombinant (B10.RFD7) also crossed over within the E_α gene and a second (B10.RPF1) crossed over within a segment located to the left of the E_α gene. This study suggests that the DNA sequence responsible for recombination in the E_α gene is also present in the B10.RPD1 and B10.RPD2 recombinant strains.     

The MHC in human bone marrow allotransplantation

In this chapter, we have considered the theoretical and practical background of bone marrow transplantation. The immune response and its regulation by genes within the major histocompatibility complex, particularly of the I region of the mouse and of the HLA-D/DR region in man, is of central importance in both graft acceptance (rejection) and graft-versus-host disease. Methods which are available for typing alleles at the HLA-A, -C, -B, -DR and complotype (BF, C2, C4A, C4B) loci, have been considered in detail. The extent to which recombination affects specific alleles on haplotypes within families is discussed, as is the occurrence of linkage disequilibrium and extended haplotypes in populations of unrelated individuals. Because the HLA-DR and complotype region in man is thought to be critical for the success of bone marrow transplantation, methods for typing of HLA-D by both the HTC and PLT approaches have been examined. Although HLA-D/DR assignments are easily made in normal subjects, they are ambiguous in about 50 per cent of candidates for bone marrow transplantation, including, particularly, patients with aplastic anaemia, leukaemia, and severe combined immunodeficiency. In this setting, it is particularly important to obtain additional information by modification of HLA-D typing procedures and through complotype and GLO allele determinations in all family members. Finally, we can hope that there will be an increased possibility of using non-family donors through methods for removing cytotoxic T cells from donor marrow and through the identification, in the general population, of individuals who are genotypically similar or identical to the recipient. In this regard, the recognition that some 30 per cent of chromosome 6 in caucasians (50 per cent of individuals) bear extended haplotypes, which include a relatively fixed set of alleles particularly in the HLA-B, -DR, complotype and GLO regions, offers considerable promise.