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M T Dorak

Publications and source records attributed to M T Dorak.

27 records · Page 2Linked to original sources
PubMed1994

Thymus-leukaemia antigens: the haemochromatosis gene product?

The gene for hereditary haemochromatosis (HFE) lies telomeric to HLA-A and is believed to be expressed in the intestinal mucosa. Its product has not been characterized, but iron overload and its pathological consequences occur only in homozygotes for this putative gene. The genes encoding the putative human counterparts of the mouse thymus-leukaemia (TL) antigens map to the area where the HFE gene lies. Here, we postulate that a human TL gene may encode a protein acting as or interacting with the transferrin (Tf) receptor in the intestinal mucosa. This hypothesis is based on the following observations: (i) hereditary haemochromatosis (HH) is due to excessive absorption of iron through the intestinal mucosa. HH has a strong association with HLA-A3, but HLA-A3 has no direct role in the pathogenesis and reflects linkage disequilibrium with a telomeric gene. (ii) An HLA-A3 homozygous genotype is associated with the highest relative risks for both early-onset leukaemia and HH. In analogy to the susceptibility locus in mice, this genotype may reflect a TL gene association in leukaemia and raise the possibility of a TL gene involvement in HH. (iii) A TL antigen-like human molecule encoded in the region telomeric to HLA-A, TCA, is expressed in leukaemia and recognized by a Tf receptor-specific monoclonal antibody. The Tf receptor is believed to have a role in the control of intestinal iron absorption. (iv) In mice, particular TL antigens are exclusively expressed in the intestinal mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Alleles at D6S265 and D6S105 define a haemochromatosis-specific genotype.

Hereditary haemochromatosis is an HLA-linked, recessive disorder with HLA-A3 a strong marker for the gene. We have identified molecular markers for two serologically indistinguishable subtypes of HLA-A3 and examined these in 42 patients with haemochromatosis. The common HLA-A3 subtype HLA-A*0301 (highly correlated with allele 1 of D6S265) was a slightly better marker for haemochromatosis (RR = 10.1, Chi2 = 30) than the serologically recognized A3 antigen (RR = 9.1; Chi2 = 27.3). Allele 8 of the more telomeric locus D6S105 was also strongly associated with haemochromatosis (RR = 13.0; Chi2 = 21.1) but alleles at this locus were not in strong linkage disequilibrium with HLA-A alleles in the control subjects. The co-occurrence of D6S265-1 and D6S105-8 alleles yielded a higher risk (RR = 16.9; Chi2 = 44). Homozygosity for the haplotype including these markers was specific for haemochromatosis, i.e. did not occur in 376 healthy subjects but was observed in 21.4% of patients. These results refine the HLA-A3 association with haemochromatosis, suggest that the haemochromatosis gene is located on the telomeric side of HLA-A and define a possible haplotype in which the first mutation may have occurred.

Adolescent↗
PubMed1994

Human major histocompatibility complex contains several leukemia susceptibility genes.

In mice, homozygosity for the Mhc haplotype H-2k is associated with increased susceptibility to spontaneous and virus-induced leukemia, lymphoma and other neoplasms in the predisposed host. The influence of the Mhc on malignant development in these models is to shorten the latency after virus inoculation. Here, we present evidence that a similar phenomenon results in early-onset of human leukemia. A molecular analysis of the MHC in 112 CML patients showed that those who developed the disease when aged less than 35 years (early-onset group) had higher homozygosity rates for the DOA1, HSP70 and C4 alleles of the DR53 group of ancestral haplotypes, for a subtype of HLA-A3, and a higher allele frequency of BfFb compared to the late-onset group. The oldest patient (n = 13) homozygous for DR53 was 52-years-old (p = 0.004), and all HLA-A3 homozygous patients (n = 4) were in the early-onset group (p = 0.01). The relative risk for early-onset CML yielded by HLA-A3 homozygosity was 17.6. The well-known serological HLA-Cw4 association was not confirmed at the DNA level and thought to be due to linkage disequilibrium with BfFb. The factor B association was sex-limited. The DR52 group haplotypes appeared to be protective. The HLA-identical sibling frequency was increased only in the early-onset group (p < 0.01). Our findings agree with the concept of an MHC influence on the development of malignancies. The similarity in the location of the susceptibility loci and the serological cross-reaction between H-2Ek and DR53 raise the possibility that the mouse and human MHC share the same leukemia susceptibility genes.

Acute Disease↗
PubMed1993

MHC class III polymorphisms in selection of donors for BMT.

Current practice for the selection of unrelated donors involves serological typing of HLA-A, -B and -DR antigens, DNA analysis of the class II region and the MLR. However, even after matching for the class II loci at the DNA level, a significant proportion of matched unrelated pairs remain MLR reactive. Ideal matching for BMT would be a match for the whole MHC haplotype rather than individual HLA loci. In the present study, we have evaluated the complementary role of class III typing in determining MHC identity. A group of 86 donor/recipient pairs, of which 14 were unrelated, was investigated using C4, Bf, HSP70 and TNF DNA probes. Phenotypically HLA-matched siblings were always identical at the C4 locus which is the most polymorphic of all the loci examined. Nine of the 14 HLA serologically matched MLR non-reactive (RRI < 20%) unrelated pairs had class III mismatching. Four of these pairs with class III mismatching were matched at the DRB and DQB loci by RFLP analysis. These results demonstrate that serological identity, DRB/DQB RFLP-matching and a negative MLR do not always match the whole haplotype in unrelated pairs. It can be concluded that the linkage of the class III loci to both HLA regions makes this region a reliable marker of the whole MHC haplotype.

Bone Marrow Transplantation↗
PubMed1992

Major histocompatibility complex, t-complex, and leukemia.

In experimental models, leukemia was the first disease shown to have an association with the major histocompatibility complex (MHC) genes. In humans, several allelic human-leukocyte antigen (HLA) associations also have been recognized. In addition to allelic associations, atypical HLA segregation patterns have been observed in leukemic families. These include a higher frequency of HLA-identical unaffected siblings, increased HLA homozygosity and increased maternal HLA-DR identity. These observations suggest preferential transmission of disease-associated haplotypes and a male transmission bias in leukemic families. The lack of disease-specific segregation, however, supports the idea that the HLA system is not directly relevant in leukemogenesis. Therefore, the existence of another genetic region linked to the MHC, causing segregation distortion, and containing recessive leukemia susceptibility genes may be postulated. The mouse t-complex would fit this model. This gene complex has recessive (semi-) lethal genes, is transmitted preferentially through fathers, and both the mouse t-complex and its rat homolog, growth and reproduction complex grc, confer susceptibility to carcinogenesis. This model could also explain the increased spontaneous abortion rate in mothers of leukemic patients, epidemiologic associations of leukemia with oral clefts and neuroectodermal tumors, and the transmission of a radiation-induced leukemia risk through fathers. Such segregation distortion might be the reason behind the maintenance of a gene(s) with a lethal effect in the population.

Animals↗
PubMedDate not supplied

Homozygous MHC genotypes and longevity.

To investigate the relevance of the major histocompatibility complex (MHC) in longevity, we carried out a molecular analysis of the MHC in 432 unrelated healthy individuals. The comparison of individuals < or = 25 years and > 25 years showed that the 5.8-kb DQA1 allele, which corresponds to HLA-DR53, was negatively associated with longevity (p = 0.0035) resulting mainly from decreased homozygosity with age for that allele (p = 0.008), and restricted to males (p = 0.008). The difference was more striking for the 5.8 kb DQA1: 9.0 kb HSP70 haplotype again only in males (26.3 vs. 6.2%; p = 0.017, OR = 5.4, 95% CI = 1.5 - 19.5). The oldest male subject homozygous for this DQA1: HSP70 haplotype was 54 years (p = 0.005). Comparing leukemic patients and healthy individuals with the same ethnic and geographical origin, homozygosity for these genotypes was more frequent in the young leukemic group. The results suggested the existence of recessive deleterious genes in a segment of HLA-DR53 haplotypes.

Adult↗
PubMedDate not supplied

HLA and leukemia: is it a simple allelic association?

The first association between a disease and MHC antigens was established for viral leukemogenesis in mice. Since then, numerous studies in humans have been carried out and the data obtained suggest that Cw3 and Cw4 may be markers for leukemia susceptibility genes. Given the relatively weak relevance of HLA-C locus antigens in immune response, unrecognized properties of Cw3 and Cw4 should be considered to explain this association. Family studies have consistently revealed limited heterogeneity of HLA antigens in those families, increased parental HLA antigen sharing resulting in increased homozygosity among offspring and high frequency of recombinations within the MHC. Furthermore, the HLA genotype of leukemic patients was found more frequently among their siblings than the anticipated 25 percent. Another significant deviation from the Mendelian expectation was increased HLA-DR identity of offspring to that of their mother in those families. These and other observations imply that in leukemia families unknown MHC-linked recessive factors linked to Cw3 and Cw4 alleles may be susceptibility genes which also cause segregation distortion of HLA genes and probably developmental errors.

Animals↗
PubMedDate not supplied

A sex-specific difference in homozygosity for HLA-DR53 in newborns.

Homozygosity for HLA-DR53 confers increased susceptibility to major forms of leukemia. In childhood leukemia, this influence is male-specific. Two separate studies have shown a male-specific increase in the homozoygosity rate for HLA-DR53 in healthy adults. This finding was attributed to possible preferential transmission of HLA-DR53 towards male offspring. If this is the case, the consequences of such a prenatal event should be evident in the newborn population. The present study investigated HLA-B and -DQA1 genotype frequencies in a sample of 134 newborns (73 boys, 61 girls) in Turkey. Restriction fragment length polymorphism (RFLP) analysis showed a homozygosity rate of 8.2 percent for HLA-DR53. Nine of 11 homozygotes were boys and the sex-specific rates were 12.3 percent vs 3.3 percent in boys and girls, respectively (p = 0.05). The DR53 homozygosity rate in males was higher than the expected rate (p = 0.02). These findings suggested a prenatal mechanism behind the excess of DR53 homozygotes in the male population. To maintain equilibrium, this excess seems to be eliminated postnatally. This model also explains how a deleterious genotype escapes natural selection.

Female↗