The major histocompatibility complex (HLA) as a genetic marker in human craniofacial anomalies

Phenotypic and molecular analyses of A/WySn mice

OBJECTIVE

Since its first description, the A strain of mice have been utilized extensively as models to study the processes involved in clefting of the midfacial region. Of the A substrains, the A/WySn has a spontaneous rate of clefting of the lip of about 20% to 30%. The A/WySn mouse model was utilized in this study to analyze and compare the phenotypic and molecular changes in the midfacial region of embryos with and without cleft.

RESULTS

Scanning electron microscopy and skeletal and cartilage preparations of newborn A/WySn pups showed the presence of bilateral and unilateral clefts of the lips and the disruption of the skeletal and cartilaginous components of the mice with clefts of the lip. The expression of the msx1 homeobox gene was analyzed by whole mount in situ hybridization of A/WySn embryos at different stages of midfacial development. The results showed that there was misregulation of the expression of the msx1 gene in embryos with cleft, with a persistence of expression in the distal growing tips of the midfacial processes and in areas that have fused in normal embryos without cleft.

CONCLUSIONS

Although the genetic defect in A/WySn mice is not known, a possible candidate gene has been mapped to a corresponding human chromosome carrying retinoic acid receptor alpha, and there exists a possibility that msx1 is in the same genetic pathway affected by the mutation of the gene in A/WySn.

Significant association of HLA-B and HLA-DRB1 alleles with cleft lip with or without cleft palate

Nucleotide sequence level typing of HLA-B, -DRB1, and -DPB1 alleles was performed on Japanese patients with cleft lip with or without cleft palate (CL/P). Two HLA-B alleles, B*1501 and B*5101, showed a significant positive association with CL/P. The increase of B*1501 was evident in female patients (OR=3.6, Pc=0.003), whereas the increase of B*5101 was evident in male patients (OR=3.7, Pc < 0.001). One HLA-DRB1 allele, HLA-DRB1*0802 also showed an increase in CL/P patients. Conversely, HLA-B*4403 and DRB1*1302 were not observed in the patient group (Pc=0.01 and Pc=0.02, respectively). No HLA-DPB1 alleles showed significant association with CL/P. Thus, the present study indicates that HLA alleles, or closely linked loci, may be involved in the pathogenesis of CL/P.

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.

Susceptibility to phenytoin-induced cleft lip with or without cleft palate: many genes are involved

In a search for genetic differences in susceptibility to cleft lip with or without cleft palate [CL(P)], congenic and recombinant inbred strains of mice were treated with phenytoin or control injections. Of six loci tested, five were found to affect susceptibility to phenytoin-induced and/or sporadic CL(P): (1) the major histocompatibility locus,H-2; (2) the locus controlling β2-microglobulin,B2m; (3) a locus controlling β-glucuronidase,Gus; (4) the locus controllingN-acetyl transferase,Nat; and (5) the locus for brown pigmentation,b. B2mandGusonly affected the sporadic incidence of CL(P), while theblocus only affected phenytoin-induced incidence of CL(P). Three of these loci are also known to affect glucocorticoid-induced isolated cleft palate (CP), but different alleles of the loci are involved. Phenytoin did not affect levels of adenosine 3′,5′-cyclic monophosphate (cAMP) in palates and tongues of day 15 fetuses. A comparison of glucocorticoid receptor parameters with the incidence of phenytoin-induced CL(P) found no correlation.

Immunologic mechanisms in the maternal-fetal relationship

Until recently, the immunologic tolerance between a mother and her allogeneic fetus has been a highly speculative and poorly understood phenomenon. New data indicate that maternal acceptance of the fetal allograft necessitates a specific, protective immune response. This specific recognition apparently involves unique placental antigens with genes that are closely linked to HLA loci. Lack of recognition of these antigens, as in matings between partners with similar HLA profiles, may result in repeated spontaneous abortions caused by unsuppressed rejection mechanisms.

Immunogenetics of development and its relationship to carcinogenesis

We have been exploring the classical idea that there is a close relationship between embryogenesis and carcinogenesis. The clinical literature provides evidence for a relationship among the presence of developmental anomalies, an increased incidence of cancer, and genes linked to the major histocompatibility complex (MHC). This relationship was explored experimentally by testing the possibility that rats having the growth and reproduction complex (grc), which causes developmental abnormalities, might be more susceptible to the development of cancer following exposure to a chemical carcinogen. Two groups of animals which were genetically similar except for the presence or absence of the grc were fed the carcinogen 2-aminoacetylfluorene. The animals carrying the grc developed the morphological changes associated with early cancer of the liver, whereas their normal counterparts did not. These susceptible animals also had a number of biochemical alterations, especially in cholesterol biosynthesis, which may be associated with the development of cancer. Molecular analysis of genomic DNA by blot hybridization revealed restriction fragment length polymorphism differences between the DNA from grc and grc+ rats, and these differences may be related to the differential susceptibility of the strains to cancer.

Histocompatibility in Italian couples with recurrent spontaneous abortions of unknown origin and with normal fertility

We investigated HLA antigen and haplotype frequencies in 47 couples with primary recurrent abortions of unknown origin, in 65 fertile couples, and in a control panel of 98 males and 92 females. A significant increase of HLA-B17 was found in abortion couples in comparison with fertile couples. No difference between abortion and control fertile couples was observed regarding HLA sharing.

Failure to detect association of isolated cleft palate with HLA antigens

HLA antigen frequencies have been determined in 282 controls and in 33 individuals with isolated cleft palate or the related birth defect velopharyngeal incompetence. No association of particular HLA antigens with this birth defect was found. A previously reported association of HLA A2 with cleft palate, in males, was not confirmed.

HLA and disease

This review describes the greater portion of a large number of new studies on HLA and disease association which has appeared in the literature since 1979. The majority of these are concerned with the association of certain diseases with class II major histocompatibility complex antigens. The possible biologic significance of these associations in terms of their probable etiology appears to be the prevailing theme. Current thinking regarding certain heritable diseases is described. It seems that although much has been done to resolve the genetics of insulin-dependent diabetes mellitus, other diseases such a multiple sclerosis still remain a mystery. Doubtlessly, much will be gained from DNA cloning and sequencing studies proposed for the future. A great deal of new information has been obtained relative to HLA itself. New loci have been postulated in the HLA-D/DR region through the use of powerful immunochemical procedures made possibly by the advent of modern technological advances. The impact of these developments on our understanding of the function of the MHC in man and its possible relationship to disease are discussed.

Major histocompatibility complex (MHC)-linked genes affecting development

Genes affecting growth and development which are linked to the major histocompatibility complex have been found in the mouse (t-complex) and in the rat (growth and reproduction complex, grc), and there is some evidence that they also exist in humans. The genes of the t-complex have different effects depending upon the specific combinations involved: skeletal and fertility abnormalities, complete or partial embryonic mortality, high transmission ratios (segregation distortion) in males, high level of linkage disequilibrium with H-2, and suppression of recombination over the adjacent portion of the chromosome. The grc in the homozygous state causes small body size, sterility in the male and reduced fertility in the female, partial embryonic mortality, and a high level of linkage disequilibrium with RT1. It also interacts epistatically with the heterozygous Tal (tail anomaly lethal) gene to cause complete embryonic death. Mice carrying t-haplotypes and rats carrying the grc have an antigen in the male germ cells which cross-reacts very strongly (t-antigen). Suggestive evidence for such genes in humans comes from (1) studies on the relationship between skeletal defects and HLA haplotypes; (2) the association of specific HLA and complement haplotypes with a high transmission ratio in males, linkage disequilibrium among certain HLA and complement specificities and suppression of recombination in some MHC haplotypes; and (3) the lack of homozygotes in an isolated inbreeding population of desert nomads (Kel Kummer Tuaregs). In addition, immunogenetic studies on couples having chronic spontaneous abortions suggest that there is an unusually high incidence of homozygosity for the HLA-D/DR and HLA-A loci in these couples, and this finding is consistent with the presence of linked loci which behave like t or grc.

Differences in frequency of cleft lip among the A strains of mice

The frequency of spontaneous cleft lip on Day 14 of gestation was examined in the A/J, A/HeJ, A/WySn, A.BY/Sn, A.SW/Sn, B10.A/SgSn, and B10.A(2R)/SgSn inbred strains of mice. A/WySn was found to have a higher frequency of cleft lip (20-30%) than A/J or A/HeJ (10%). Differences among strains in laterality of clefting and in rates of differential mortality of affected embryos were also found. Results of crosses between A/WySn and A/HeJ suggested that the difference in rate of clefting may be due to a genetic maternal effect. The results for A.BY/Sn, A.SW/Sn, B10.A/SgSn and B10.A(2R)/SgSn indicated that no association of cleft lip liability and the H-2 complex was detectable.

Maternal influences on congenital craniofacial malformations

Congenital craniofacial malformations represent an extremely complex biomedical problem area. The complexity includes early detection, diagnosis, treatment, habilitation, and, of course, prevention. The genetic and environmental issues which appear to interact and result in congenital malformations are becoming better understood. Rapid advances in mouse and human immunogenetics indicate several possible explanations as to why some individuals acquire certain birth defects whereas other individuals do not express congenital malformations. Recent discoveries concerning the major histocompatibility complex (MHC) and associations with a number of human malformations have stimulated interesting speculations concerning genetic and environmental factors which might be responsible for predispositions to congenital malformations. Of particular interest is the possible function of the major histocompatibility complex of the mother during early stages of embryogenesis and how this assembly of genes may confer susceptibility to environmentally induced birth defects in mouse and human reproduction.