Minor Susceptibility Research Articles

Segregation of autoimmune type 1 diabetes in a cross between diabetic BB and brown Norway rats.

Diabetes-prone DP-BB rats spontaneously develop insulin-dependent diabetes mellitus resembling type 1 diabetes mellitus in man. Expression of T cell lymphopenia and presence of at least one class II major histocompatibility complex (MHC) RT1u haplotype are required for development of diabetes. Diabetes segregation was studied in lymphopenic backcross (BC) offspring from a cross between male DP-BB/HRI and female BN/Mol rats. Diabetes occurred in 75% of BC rats with genotype RT1u/u and in 18% of those being RT1n/u in genotype. The latter developed diabetes significantly later than MHC homozygotes and parental DP-BBs. Our data further point to the existence of additional genes of minor importance for development of IDDM. One of these seemed to be positioned on the X chromosome. The recently published linkage to chromosome 18 could not be confirmed however. Finally, the BN-derived non-albino allele of the C gene was associated with higher diabetes incidence. This points to the existence of minor susceptibility genes in other strains of rats.

Linkage of type I diabetes to 15q26 (IDDM3) in the Danish population.

Affected sib pair and linkage disequilibrium analysis, intrafamilial and case-control association studies were performed on 81 Danish multiplex insulin-dependent diabetes mellitus (IDDM) families (382 individuals) and 82 healthy Danish controls. The results confirm the linkage of D15S107 to IDDM in these Danish IDDM families (P = 0.010). When these data are combined with those of previous studies, an even stronger case for linkage can be made (P = 0.0005). Our analyses show that the D15S107*130 allele provides increased susceptibility (P = 0.02, relative risk = 3.55) and that the D15S107 locus contributes up to 16% of the familial clustering of IDDM. The analysis of affected sib pairs suggests that HLA and D15S107 may possibly act independently of each other. Taken together with our previous findings, our results suggest that three causes of susceptibilities can be discerned in the IDDM patient population: (1) a major susceptibility caused by the HLA-DRB1 alleles; (2) a minor susceptibility caused by the joint action of HLA and other non-HLA gene(s); and (3) a minor susceptibility caused by non-HLA gene(s).

Human muscle acetylcholine receptor alpha-subunit gene (CHRNA1) association with autoimmune myasthenia gravis in black, mixed-ancestry and Caucasian subjects.

We have sought associations with the muscle acetylcholine receptor alpha-subunit gene (CHRNA1) in autoimmune myasthenia gravis (MG) patients from three ethnic groups; Caucasians and South Africans of Black and Mixed-Ancestry. We found a significant association with the HB*15 CA repeat allele in unrelated Black myasthenics (n = 18; RR = 2.85; pX2 = 0.04) compared with 52 ethnically matched controls. A family-based association study and linkage analysis in Caucasian simplex and multiplex families supported a positive association at this locus with the longer alleles, including HB*14 to *18. However, no significant cosegregation of the disease with the HB alleles could be demonstrated in affected sib pairs. Our results suggest that the CHRNA1 locus harbours a minor susceptibility gene for developing MG, though we cannot rule out linkage disequilibrium with another major gene locus on chromosome 2.

Polymorphic nucleotides within the human IL-4 promoter that mediate overexpression of the gene.

Atopy, which predisposes individuals to develop asthma, severe systemic anaphylaxis, and atopic dermatitis, is usually associated with dramatically elevated total serum IgE levels and is thought to be controlled by a major susceptibility gene and multiple minor susceptibility genes. A recent sib-pair analysis revealed a tight linkage between markers on 5q31.1 and a major susceptibility gene controlling total serum IgE levels. Due to its location within this cluster and its biologic role in Ig class switching and Th2 cell differentiation, the IL-4 gene has emerged as one major candidate for the atopy gene. In one model, polymorphisms within IL-4 regulatory elements might result in overexpression of the gene, amplifying Th2 cell differentiation and class switching to IgE. In support of this model, we report that the human IL-4 promoter exists in multiple allelic forms that exhibit distinct transcriptional activities in IL-4-positive T cells. A particular allele has an unusually high transcriptional activity. A nucleotide substitution within a recently described OAP40 element located just upstream of an NF-AT site (P sequence) appears to be largely responsible for the increased promotor strength of this particular allelic form of the IL-4 promoter. In EMSAs, this substitution results in a markedly enhanced affinity for sequence-specific complexes exhibiting an AP-1 specificity. The identification of allelic nucleotides, which results in overexpression of the IL-4 gene, provides specific targets for a comprehensive screening of atopic and nonatopic individuals and may provide a clue for genetic predisposition for atopy.

ChemInform Abstract: AXIAL‐BIAXIAL PHASE TRANSITION IN DISCOTIC LIQUID CRYSTALS, STUDIED BY DEUTERIUM NMR

Truxenehexaalkanoates (TxHAn) exhibit a variety of discotic mesophases including the sequence ND⇄Drd⇄Dho. The ordering characteristics of these phases were studied by deuterium NMR of deuterated solutes, in particular C6D6. The results indicate that during the phase transition the minor susceptibility axis of the Drd phase transforms into the director axis of the axial phases. It is suggested that in the Drd phase, in alternating columns the mesogen molecules are tilted with respect to the columns axes in opposite directions.

Axial–biaxial phase transition in discotic liquid crystals, studied by deuterium NMR

Truxenehexaalkanoates (TxHAn) exhibit a variety of discotic mesophases including the sequence ND⇄Drd⇄Dho. The ordering characteristics of these phases were studied by deuterium NMR of deuterated solutes, in particular C6D6. The results indicate that during the phase transition the minor susceptibility axis of the Drd phase transforms into the director axis of the axial phases. It is suggested that in the Drd phase, in alternating columns the mesogen molecules are tilted with respect to the columns axes in opposite directions.