Biomedical subjects

Hans Ackerman

Publications and source records attributed to Hans Ackerman.

4 recordsLinked to original sources

PubMed2003

Haplotypic analysis of the TNF locus by association efficiency and entropy.

BACKGROUND: To understand the causal basis of TNF associations with disease, it is necessary to understand the haplotypic structure of this locus. We genotyped 12 single-nucleotide polymorphisms (SNPs) distributed over 4.3 kilobases in 296 healthy, unrelated Gambian and Malawian adults. We generated 592 high-quality haplotypes by integrating family- and population-based reconstruction methods. RESULTS: We found 32 different haplotypes, of which 13 were shared between the two populations. Both populations were haplotypically diverse (gene diversity = 0.80, Gambia; 0.85, Malawi) and significantly differentiated (p < 10-5 by exact test). More than a quarter of marker pairs showed evidence of intragenic recombination (29% Gambia; 27% Malawi). We applied two new methods of analyzing haplotypic data: association efficiency analysis (AEA), which describes the ability of each SNP to detect every other SNP in a case-control scenario; and the entropy maximization method (EMM), which selects the subset of SNPs that most effectively dissects the underlying haplotypic structure. AEA revealed that many SNPs in TNF are poor markers of each other. The EMM showed that 8 of 12 SNPs (Gambia) and 7 of 12 SNPs (Malawi) are required to describe 95% of the haplotypic diversity. CONCLUSIONS: The TNF locus in the Gambian and Malawi sample is haplotypically diverse and has a rich history of intragenic recombination. As a consequence, a large proportion of TNF SNPs must be typed to detect a disease-modifying SNP at this locus. The most informative subset of SNPs to genotype differs between the two populations.

Adult↗

PubMed2003

Nucleotide and haplotypic diversity of the NOS2A promoter region and its relationship to cerebral malaria.

To assess the hypothesis that nitric oxide is critical in the pathogenesis of cerebral malaria, we analysed genetic variation in the proximal promoter region of NOS2A, the gene encoding inducible nitric oxide synthase. Sequencing 72 Gambian chromosomes revealed 11 single nucleotide polymorphisms in 2.5 kB (theta=8.6 x 10(-4)). Genotyping 104 nuclear families identified six common haplotypes. A single haplotype, uniquely defined by the NOS2A-1659T allele, was associated with cerebral malaria by a transmission disequilibrium test of 334 affected children and their parents (P=0.02). An independent case-control study of 505 different children from the same population replicated the allelic association with cerebral malaria (odds ratio: 1.31, P=0.04). Taken together these data indicate a weak but significant association of the NOS2A locus with susceptibility to cerebral malaria. Despite high linkage disequilibrium across the region studied, this association would not have been detected without the initial construction of a dense marker set for haplotype tagging.

Alleles↗

PubMed2003

The effect of HLA-DR on susceptibility to rheumatoid arthritis is influenced by the associated lymphotoxin alpha-tumor necrosis factor haplotype.

OBJECTIVE: HLA-DRB1, a major genetic determinant of susceptibility to rheumatoid arthritis (RA), is located within 1,000 kb of the gene encoding tumor necrosis factor (TNF). Because certain HLA-DRB1*04 subtypes increase susceptibility to RA, investigation of the role of the TNF gene is complicated by linkage disequilibrium (LD) between TNF and DRB1 alleles. By adequately controlling for this LD, we aimed to investigate the presence of additional major histocompatibility complex (MHC) susceptibility genes. METHODS: We identified 274 HLA-DRB1*04-positive cases of RA and 271 HLA-DRB1*04-positive population controls. Each subject was typed for 6 single-nucleotide polymorphisms within a 4.5-kb region encompassing TNF and lymphotoxin alpha (LTA). LTA-TNF haplotypes in these unrelated individuals were determined using a combination of family data and the PHASE software program. RESULTS: Significant differences in LTA-TNF haplotype frequencies were observed between different subtypes of HLA-DRB1*04. The LTA-TNF haplotypes observed were very restricted, with only 4 haplotypes constituting 81% of all haplotypes present. Among individuals carrying DRB1*0401, the LTA-TNF 2 haplotype was significantly underrepresented in cases compared with controls (odds ratio 0.5 [95% confidence interval 0.3-0.8], P = 0.007), while in those with DRB1*0404, the opposite effect was observed (P = 0.007). CONCLUSION: These findings suggest that the MHC contains genetic elements outside the LTA-TNF region that modify the effect of HLA-DRB1 on susceptibility to RA.

Arthritis, Rheumatoid↗

PubMed2002

Evolution of a polymorphic regulatory element in interferon-gamma through transposition and mutation.

Mammalian transposable elements have intrinsic regulatory elements that can activate neighboring genes, and it is speculated that they can also carry extrinsic transactivating DNA sequences to new genomic locations. We have identified a polymorphic segment of the human interferon-gamma promoter region where two adjacent binding sites for NF-kappaB and NFAT originated from the insertion of an Alu element approximately 22-34 MYA. Both binding sites lie outside the Alu consensus sequence but within the boundaries of the insertion, suggesting that this segment of DNA was comobilized when the Alu element moved from another part of the genome. Sequence comparisons and examination of DNA-protein interactions across nine different primate species indicate that the inserted sequence contained the intact NFAT binding site, whereas the ability to bind NF-kappaB evolved through a series of mutations after the insertion. These observations are consistent with the notion that retropseudogenes can comobilize intact regulatory sequences to new locations and thereby influence the evolution of gene regulatory networks; however, the extent to which such events have shaped the evolution of gene regulation remains unknown.

Alu Elements↗