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.     

Definitive RFLPs to distinguish between the human complement C4A/C4B isotypes and the major Rodgers/Chido determinants: Application to the study of C4 null alleles

Definitive restriction fragment length polymorphisms (RFLPs) representing the exact locations responsible for isotypicity between the human complement components C4A and C4B, and their generally associated major Rodgers (Rg1) and Chido (Ch1) antigenic determinants, have been designed. By means of a C4d-specific genomic probe for Southern blot analysis, a C4A gene can be defined by the presence of the 276 bp and 191 bp N 1 a IV fragments, while a C4B gene can be defined by a single 467 bp N1aIV fragment. In addition, an Rgl-expressing C4 gene can be represented by a 565 bp EcoO 109 fragment, and a Chl-expressing C4 gene by a 458 by EcoO 109 fragment, under the same conditions. All these polymorphic restriction fragments can be unambiguously and conveniently detected. In combination with the Taq I polymorphic patterns specific for the C4 loci and for the neighboring 21-hydroxylase genes, the nature and structure of the tandem C4,21-hydroxylase gene complex can be elucidated. In this study, it is inferred that the null allele of the HLA haplotype B44 DR6 C4A3 C4BQO is not a C4B allele, but probably encodes another C4A 3 allotype at the second C4 locus.Abbreviations used in this paper C4 (long) - C4 gene of 22 kb, with a 6–7 kb intron - C4 (short) - C4 gene of 16 kb, without a 6–7 kb intron; complotype SCO1, factor B S, C2 C, C4A QO; C4B 1 Dedicated to the memory of our teacher, the late Professor Rodney Porter C. H. F. R. S.     

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.     

Null alleles of the fourth component of complement and HLA haplotypes in familial systemic lupus erythematosus

Eight families (121 individuals) with two or more members affected with systemic lupus erythematosus (SLE) were analyzed for histocompatibility antigens (HLA-A, B, C, DR, MT, and MB) and complement antigens (C4A, C4B, and BF). These data were correlated with serological markers (antinuclear antibodies, single- and double-stranded anti-DNA, anti-SM, anti-nRNP, anti-Ro [SS-A], anti-La [SS-B], and biological false-positive tests for syphilis and clinical features. Fifteen members had SLE, and 19 had other immune diseases (subacute cutaneous lupus erythematosus, discoid lupus erythematosus, hypothyroidism, insulin-dependent diabetes mellitus, primary, Sjogren's syndrome, immune thrombocytopenic purpura, rheumatoid arthritis, and multiple sclerosis). Twenty-three healthy relatives (seroreactors) had significant titers of circulating antibodies, as did 2 of 17 spouses. There was an increased frequency of null C4 alleles in those individuals with SLE (60%) and healthy relatives (50%) as compared with spouses (24%). Multivariate analysis showed a significant association between SLE and female sex (P=.006), whereas there was no significant association revealed between female sex and other immune diseases. Patients with SLE also had a higher frequency of either C4A or C4B null alleles (P=.01) than those with immune diseases. The C4A homozygous null phenotype was more common in SLE patients than in seroreactors (P=.02). There was a higher frequency of HLA-DR2 and DR3 in individuals with SLE than in those with immune disease (P=.08), seroreactors (P=.02) and normal relatives (P =.002). One totally C4-deficient patient with SLE was identified. These families demonstrate an important association between SLE and the C4 null allele and the HLA-DR2 and DR3. These risk factors, however, cannot account for the development of disease in all individuals.     

C4A gene deletion and HLA associations in black Americans with systemic lupus erythematosus

In North America and European Caucasoids with systemic lupus erythematosus (SLE) there is an increased frequency of aC4A, CYP21A gene deletion, largely associated with theHLA-B8,DR3,C4A ^* QO extended haplotype. There have been no consistent HLA associations reported for SLE in blacks, although an increased frequency of serologically determinedC4A null alleles has been reported in two studies. We studied 79 black American SLE patients and 68 black controls by restriction fragment length polymorphism analysis to dermine if aC4A gene deletion was a genetic risk factor for SLE. Moreover, the nature of the deletion and any HLA phenotypic associations were sought. Nineteen of 79 (24%) patients compared to 5 of 68 (7.4%) controls had a phenotypicC4A,CYP21A gene deletion (P=.005; RR=4). A homozygous deletion in four patients gave a genotypic frequency of 23/158 (14.5%) SLE patients vs 5/136 (3.7%) controls (P=.001; RR=4.5). The deletion was associated with HLA-DR2 (P=.03) and HLA-DR3 (P=.03). Moreover, all subjects with the deletion had HLA-DR2 or DR3 (P=7.7×10⁻⁶). HLA-B44 was also associated with the deletion (P=.02), and eight of the nine HLA-B44 positives also carried HLA-DR2. HLA-B8 approached significance (P=.08) and was always accompanied by HLA-DR3. Finally, this black population demonstrated a uniqueC4B gene size polymorphism with 80% C4B “short” as compared to the 40% C4B “short” frequency reported in whites. We conclude that a largeC4A,CYP21A gene deletion, particularly associated with theHLA-B44,-DR2, and-DR3 alleles, is the strongest genetic risk factor thus far identified for SLE susceptibility in black Americans. Furthermore, the unique preponderance of theC4B “short” gene form may be a factor in the actual formation of the deletion.     

Immunofixation for C2 typing: C2 allotypes in Spaniards in relation to HLA,Bf and C4

Summary C2 typing is performed by immunofixation with anti-C2 antiserum instead of by a hemolytic overlay. This method gives sharp band definition, is less cumbersome than the hemolytic overlay, gel files are easily made, and it also enables one to describe putative new nonhemolytic variants. C2 allele frequencies were studied in a sample of the normal Spanish population and were found to be similar to other Caucasoids. HLA-Bw62,-Cw3, and-DR4 were significantly associated with C2 B. Concordantly, the only C2^*B extended HLA haplotype found in family material was Bw62-Cw3-Bw6-(DR4)-Bf^*S-C2^*B-C4A^*3 B^*2-(GLO^*1). C4A^*4 B^*2 and C4A^*4 B^*4 are not found within the same haplotype together with C2^*B and Bw62 or Bw22 respectively, nor do other C2^*B haplotypes occur with common HLA-B alleles. These results may favour the hypothesis that the Bw62-C2^*B haplotype is produced by one mutation arising in the Bw62-C2^*C haplotype and that subsequent crossovers can explain other C2^*B haplotypes (including Bw22-C2^*B).     

Association of polymorphisms in the HLA-B region with extended haplotypes

Genomic probes from the HLA-B region of the major histocompatibility complex (MHC) were used to study the association of restriction fragment length polymorphisms (RFLPs) with various MHC alleles, complotypes, and extended haplotypes. The two DNA probes, M20A and R5A, were derived from previously cloned cosmids and are located 38 and 110 kilobases (kb) centromeric to HLa-B, respectively. Five different RFLP variants occuring in five different haplotypic combinations were detected within a panel of 40 homozygous-typing cells and cells from 21 families using Bst EII. In two informative families with HLA-B/DR recombinations the inheritance of the RFLP variants was consistent with their mapping between HLA-B and complotypes. The R5A/M20A haplotypic pattern 6.5 kb/3.0 kb (A) had a normal Caucasian frequency of approximately 0.43 and was found in all independent examples of the extended haplotypes [HLA-B8,SC01,DR3], [HLA-B18,F1C30, DR3], [HLa-Bw62,SC33,Dr4], [HLa-B44,SC30,Dr4], and [HLA-Bw47,FC91,0DR7]. The patterns of 6.9 kb/ 3.0 kb (B), 6.5 kb/4.7 kb (C), 1.45 kb/3.0 kb (D), and 6.9 kb/4.7 kb (E) had normal Caucasian frequencies of approximately 0.23, 0.15, 0.15, and 0.04 and were found on all independent examples of [HLA-B38,SC21, DR4], [HLA-Bw57,SC61,DR7], [HLA-B7,SC31,DR2], and [HLA-B44,FC31,DR7], respectively. Individual complotypes or HLA-B alleles which were markers of extended haplotypes showed variable associations. For example, HLA-B7 and the complotype SC31 were associated with all R5A/M20A RFLP haplotypes except haplotype E, although [HLA-B7,SC31,DR7] was associated exclusively with haplotype D. HLA-B27, not known to be part of an extended haplotype, was suprisingly exclusively associated with the 6.5 kb/4.7 kb or C haplotypic pattern in all five instances tested. These findings support the concept of regional conservation of DNA on independent examples of extended haplotypes. The results also further characterize these haplotypes.     

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.     

Family studies of IgA deficiency

Seventeen immunoglobulin A (IgA)-deficient subjects and other members from 13 families were examined at HLA-A, B and DR, C4A, C4B, and Bf loci. Of the 29 independent haplotypes in the IgA-deficient: subjects, 22 included deletions, duplications, or defects at the C4 or 21-hydroxylase loci. It is suggested that there may be a gene regulating serum IgA concentrations in this same region of chromosome 6. Three main supratypes explain most of the previously reported tHLA associations with IgA deficiency. These are A1, Cw7, B8, C4AQ0, C4B1, BfS, DR3, Bw65(14), C4A2, C4B1/2, BfS, and Bw57(17), C4A6, C4B1, BfS. All three are proposed to carry a gene for IgA deficiency, while other supratypes carrying the same B allele generally do not. Other supratypes possibly associated with IgA deficiency were also identified. A survey of about 150 individuals with at least 1 of the 3 main supratypes revealed only 2 IgA-deficient subjects, and these were among the 20 that had 2 of these supratypes. This suggests the possibility of a recessive mode of inheritance, with penetrance determined by another factor which is not major histocompatibility complex-linked. All the supratypes found in this group of IgA-deficient subjects would then carry the putative recessive allele for IgA deficiency.     

HLA Haplotypes with C4B5; evidence for further allelic heterogeneity

Twenty-three individuals from various disease groups and normal controls were identified by immunofixation with anti-C4, C4-dependent lysis, determination of Rg (Rodgers) and Ch (Chido) phenotypes, and immunoblotting with C4-specific mouse monoclonal antibody. We found that one haplotype predominates with the C4B ^* 5 allele, HLA-A11, B22(55), Cw3, Bf ^* S, C4A ^* 4B ^* 5, which also carries the Ch ^{1,–2, 3} haplotype. The B5 allotype was also found with HLA-1360, HLA-1335 in Caucasoids, and HLA-B18 in non-Caucasoids; these carried the Ch ^{–1, –2, –3} haplotype. Our results are in accord with an earlier report of two B5 subtypes, B5Rg⁺ and B5Rg^– (Roos et al. 1984). The specificity of the mouse monoclonal antibodies IC4 and 21312 had been previously related to C4A and C4B, respectively, but our results suggest that they relate more closely to Rg and Ch determinants.     

Level of Trace Elements (Copper,Zinc, Magnesium and Selenium) and Toxic Elements (Lead and Mercury) in the Hair and Nail of Children with Autism

Autism is a multi-factorial pathology observed in children with altered levels of essential and elevated levels of toxic elements. There are also studies reporting a decrease in nutritional trace elements in the hair and nail of autistic children with healthy controls; moreover, bioelements have been shown to play an important role in the central nervous system. Therefore, the purpose of the present study was to assess the levels of trace elements like copper (Cu), zinc (Zn), magnesium (Mg), and selenium (Se) and toxic elements like mercury (Hg), and lead (Pb) in the hair and nail samples of autistic children and to evaluate whether the level of these elements could be correlated with the severity of autism. The subjects of the study were 45 autistic children with different grades of severity (low (LFA), medium (MFA), and high (HFA) functioning autism) according to Childhood Autism Rating Scale, n = 15 children in each group and 50 healthy children (age and sex matched). The boys and girls ratio involved in this study was 4:1, and they were 4-12 years of age. The study observed a valid indication of Cu body burden in the autistic children. The children with different grades of autism showed high significance (p < 0.001) in the level of copper in their hair and nail samples when compared to healthy controls. The level of Cu in the autistic children could be correlated with their degree of severity (more the Cu burden severe is autism). The study showed a significant elevation (p < 0.001) in the levels of toxic metals Pb and Hg in both hair and nail samples of autistic children when compared to healthy control group. The elevation was much pronounced in LFA group subjects when compared among autistic groups MFA and HFA. The levels of trace elements Mg and Se were significantly decreased (p < 0.001) in autistic children when compared to control. The trace element Zn showed significant variation in both hair and nails of LFA group children when compared to control group and other study groups. The significant elevation in the concentration of Cu, Pb, and Hg and significant decrease in the concentration of Mg and Se observed in the hair and nail samples of autistic subjects could be well correlated with their degrees of severity.     

Complement C4 and heat shock protein 70 (HSP70) genotypes and type I diabetes mellitus

Type I diabetes is strongly associated with the major histocompatibility complex (MHC) class II region (DR and DQ loci), and to a lesser extent the class III region (complement C4 loci). Restriction fragment length polymorphism analysis was employed to investigate the C4 and heat shock protein 70 (HSP70) loci of 176 patients with type I diabetes and 92 healthy controls. In the patient population there was an excess of deletions of the C4A locus (48.5% vs 22.1%, P < 0.0005). The HSP70 probe in conjunction with the restriction endonuclease Pst I detects two alleles of 9 or 8.5 kilobases (kb). The 8.5 kb allele was significantly increased in the patient group compared to healthy controls (0.569 vs 0.353, respectively, P < 0.0005). Furthermore, a C4A deletion nearly always occurred with the 8.5 kb HSP70 allele, suggesting that it may be a marker of the HLA-A1, B8, C4A deletion, DR3 extended haplotype.     

Glucose-6-phosphate dehydrogenase (G6PD) electrophoretic variants and the PvuII polymorphism in Southern African populations

Summary Southern African Bantu-speaking negroid and San populations were examined with regard to the glucose-6-phosphate dehydrogenase (G6PD) PvuII restriction fragment length polymorphism (RFLP) showing alleles of 4kb and 1.6 kb, called Type 1 and Type 2, respectively. The standardized disequilibrium coefficient for the electrophoretic G6PD types and PvuII alleles in the Southern African population was 0.28. The molecular lesion causing the Gd^A mutation is the same in the San and Southern African negroid populations. Gd^A chromosomes are found in association with both the Type 1 and Type 2 alleles, whereas none of the 62 Gd^B chromosomes from the Southern African populations had the Type 2 allele. Five of the 44 Gd^B chromosomes studied in the American Black population had the Type 2 allele, indicating that the Gd^B allele in the two populations may have different origins. The presence of all 3 A^– deficiency mutations in the G6PD A gene, in a region where the ancestral population was thought to have predominantly G6PD B, may be explained by their origin in Africa after the divergence of the races.     

Genetic Variants of Angiotensin-Converting Enzyme Are Linked to Autism: A Case-Control Study

BackgroundAutism is a disease of complex nature with a significant genetic component. The importance of renin-angiotensin system (RAS) elements in cognition and behavior besides the interaction of angiotensin II (Ang II), the main product of angiotensin-converting enzyme (ACE), with neurotransmitters in CNS, especially dopamine, proposes the involvement of RAS in autism. Since the genetic architecture of autism has remained elusive, here we postulated that genetic variations in RAS are associated with autism.MethodsConsidering the relation between the three polymorphisms of ACE (I/D, rs4343 and rs4291) with the level of ACE activity, we have investigated this association with autism, in a case-control study. Genotype and allele frequencies of polymorphisms were determined in DNAs extracted from venous blood of 120 autistic patients and their age and sex-matched healthy controls, using polymerase chain reaction (PCR) and PCR–restriction fragment length polymorphism (PCR–RFLP) methods.ResultsThere were strong associations between both DD genotype of ACE I/D and the D allele, with autism (P = 0.006, OR = 2.9, 95% CI = 1.64–5.13 and P = 0.006, OR = 2.18, 95% CI = 1.37–3.48 respectively). Furthermore, a significant association between the G allele of rs4343 and autism was observed (P = 0.006, OR = 1.84, 95%CI = 1.26–2.67). Moreover, haplotype analysis revealed an association between DTG haplotype and autism (P = 0.008).ConclusionOur data suggests the involvement of RAS genetic diversity in increasing the risk of autism.     

The “Sardinian”HLA-A30,B18,DR3,DQw2 haplotype constantly lacks the21-OHA andC4B genes. Is it an ancestral haplotype without duplication?

TheC4 and21-OH loci of the class III HLA have been studied by specific DNA probes and the restriction enzymeTaq I in 24 unrelated Sardinian individuals selected from completely HLA-typed families. All 24 individuals had theHLA extended haplotypeA30,Cw5,B18, BfF1,DR3,DRw52,DQw2, named “Sardinian” in the present paper because of its frquency of 15% in the Sardinian population. Eighteen of these were homozygous for the entire haplotype, and six were heterozygous at theA locus and blank (or homozygous) at all the other loci. In all completely homozygous cells and in four heterozygous cells at theA locus, the restriction fragments of the21-OHA (3.2 kb) andC4B (5.8 kb or 5.4 kb) genes were absent, and the fragments of theC4A (7.0 kb) and21-OHB (3.7 kb) genes were present. It is suggested that the “Sardinian” haplotype is an ancestral haplotype without duplication of theC4 and21-OH genes, practically always identical in its structure, also in unrelated individuals. The diversity of this haplotype in the class III region (about 30 kb less) may be at least partially responsible for its misalignment with most haplotypes, which have duplicatedC4 and21-OH genes, and therefore also for its decreased probability to recombine. This can help explain its high stability and frequency in the Sardinian population. The same conclusion can be suggested for the Caucasian extended haplotypeA1,B8,DR3 that always seems to lack theC4A and21-OHA genes.     

Heterogeneity of human C4 gene size

In this article we present a study showing that the human C4 genes differ in length because of the presence or absence of a 6.5 kb intron near the 5 end of the gene. DNA from individuals of known HLA, factor B, and C4 haplotypes was analyzed for restriction fragment length polymorphism (RFLP) by Southern blot analysis with C4-specific cDNA probes. The RFLP patterns obtained showed that the C4 genes are either 22.5 kb or 16 kb in length. They are referred to as long and short C4 genes, respectively. A population study was carried out to examine the distribution of the gene size according to C4 allotypes and haplotypes. Long C4 genes included all C4A genes studied and also some C4B allotypes, e. g., B1 on most C4 A3B1 haplotypes. Similarly, C4B null genes were found to be of the long form. Other C4B allotypes tested were found to be coded for by short C4 genes, including B2, B1 in C4 A6B1 and C4 AQOB1 (with a single C4B gene haplotype).Abbreviations used in this paper C4 fourth component of complement - C2 second component of complement - BF factor B - MHC major histocompatibility complex - RFLP restriction fragment length polymorphism - EDTA ethylenediaminetetraacetic acid - SDS lauryl sulfate, sodium salt     

The study of a French family with two duplicated C4A haplotypes

Summary The finding of two duplicated C4A haplotypes in a normal French family led to a detailed study of their C4 polymorphism. The father had an extremely rare A^*6A^*11, B^* QO haplotype inherited by all of his children and the mother had the more common A^*3A^*2, B^*QO haplotype. Two HLA identical daughters only have four C4A alleles. The father's A11 allotype expresses Ch: 1 (Chido) rather than Rg:1 (Rodgers) and represents a new Ch phenotype Ch: 1,-2,-3,-4,-5,-6. In order to clarify the genetic background in this unusual family, DNA studies of restriction fragment length polymorphisms (RFLPs) were undertake. The father's rare haplotype, which expresses two C4A allotypes, results from a long and a short C4 gene normally associated with the A^*6, B^*1 that also exhibits the BglII RFLP. As it travels in an extended MHC haplotype HLA A2, B57 (17), C2^*C, BF^*S, DR7 that is most frequently associated with A^*6, B^*1, we postulate that the short C4B has been converted in the chain region to a C4A gene which produces a C4A protein. This report of a short C4A gene is the first example in the complex polymorphism of C4.     

Studies of HLA, factor B (Bf), complement C2 and C4 haplotypes in type 1 diabetic and control families from northern Sweden

The HLA-A,-B,-C,-DR antigens and the complement factors C2, C4 and Bf were determined in 30 insulin-dependent diabetes mellitus (IDDM) patients and 30 healthy controls from northern Sweden. Family studies allowed the deduction of extended haplotypes in the HLA and complement systems. Phenotype studies revealed significant associations between IDDM and HLA-DR4 (p less than 0.001), HLA-DR3 (p less than 0.05), HLA-DR3/4 (p less than 0.025), C4-B3 (p less than 0.001) and Bf-S (p less than 0.025). Haplotype studies showed that the extended haplotype [HLA-B15, C2-1, C4-A3B3, Bf-S, HLA-DR4] had a particularly strong association to IDDM. This haplotype was found in 10 out of 30 IDDM probands but in none of 30 control children and accounts for practically all the C4-B3 allotypes among the 30 IDDM probands. The C4-B3 gene therefore seems to be a valuable marker for IDDM. No haplotype containing HLA-DR3 was increased in frequency among the IDDM probands. The extended haplotype [HLA-B7, C2-1, C4-A3B1, Bf-S, HLA-DR2] present among the controls was absent in the IDDM probands. The frequency of the extended haplotype [HLA-B15, C2-1, C4-A3B3, Bf-S, HLA-DR4] was increased also among the parents to the IDDM probands compared to those of the control parents, whereas the frequency of [HLA-B7, C2-1, C4-A3B1, Bf-S, HLA-DR2] was decreased. The extended haplotype [HLA-B8, C2-1, C4-B1, Bf-S, HLA-DR3] was more common among the males (p less than 0.05) compared to the females in the total material. The family analysis showed that 3 out of 5 affected sibs shared both haplotypes with their IDDM proband. This was the case for only 3 out of 35 unaffected sibs.