Mutations in ENPP1 are associated with 'idiopathic' infantile arterial calcification.

Idiopathic infantile arterial calcification (IIAC; OMIM 208000) is characterized by calcification of the internal elastic lamina of muscular arteries and stenosis due to myointimal proliferation. We analyzed affected individuals from 11 unrelated kindreds and found that IIAC was associated with mutations that inactivated ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). This cell surface enzyme generates inorganic pyrophosphate (PP(i)), a solute that regulates cell differentiation and serves as an essential physiologic inhibitor of calcification.

Association of the HLA region with multiple sclerosis as confirmed by a genome screen using >10,000 SNPs on DNA chips.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system, with a complex genetic background. Here, we present a genome screen for association in small scale, employing 11,555 single nucleotide polymorphisms (SNPs) on DNA chips for genotyping 100 MS patients stratified for HLA-DR2+ and 100 controls. More than 500 SNPs revealed significant differences between cases and controls before Bonferroni correction. A fraction of these SNPs was reanalysed in two additional cohorts of patients and controls, using high-throughput genotyping methods. A marker on chromosome 6p21.32 (rs2395182) yielded the highest significance level, validating the established HLA-DR association.

Application of genomewide SNP arrays for detection of simulated susceptibility loci.

The prospect of SNP-based genomewide association analysis has been extensively discussed, but practical experiences remain limited. We performed an association study using a recently developed array of 11,555 SNPs distributed throughout the human genome. A total of 104 DNA samples were hybridized to these chips with an average call rate of 97% (range 85.3-98.6%). The resulting genomewide scans were applied to distinguish between carriers and noncarriers of 37 test variants, used as surrogates for monogenic disease traits. The test variants were not contained in the chip and had been determined by other methods. Without adjustment for multiple testing, the procedure detected 24% of the test variants, but the positive predictive value was low (2%). Adjustment for multiple testing eliminated most false-positive associations, but the share of true positive associations decreased to 10-12%. We also simulated fine-mapping of susceptibility loci by restricting testing to the immediate neighborhood of test variants (+/-5 Mb). This increased the proportion of correctly identified test variants to 22-27%. Simulation of a bigenic inheritance reduced the sensitivity to 1%. Similarly adverse effect had reduction of allelic penetrance. In summary, we demonstrate the feasibility and considerable specificity of SNP array-based association studies to detect variants underlying monogenic, highly penetrant traits. The outcome is affected by allelic frequencies of chip SNPs, by the ratio between simulated "cases" and "controls," and by the degree of linkage disequilibrium. A major improvement is expected from raising the density of the SNP array.

Association of ANKH gene polymorphisms with radiographic hand bone size and geometry in a Chuvasha population.

We performed a family-based association study to test the hypothesis that genetic variation at the human orthologue of the mouse progressive ankylosis gene (ANKH) is involved in determining bone size (BS) and bone geometry (BG). The study population comprised 126 nuclear families with 574 adult Chuvashian individuals living in small villages in the Russian Federation. Quantitative bone traits were determined by analyzing plain hand radiographs. Familial correlations for all studied traits revealed a high degree of heritability in this ethnically homogeneous population. Three simple tandem repeat (STR) polymorphisms, one intragenic and two flanking markers, as well as six single nucleotide polymorphisms (SNPs) were tested. The SNPs were detected by re-sequencing experiments and covered ANKH exons with their flanking splice sites and the promoter region. We used three different transmission disequilibrium tests (TDTs) and obtained multiple significant association signals for all investigated bone traits. Alleles of several markers located at different positions of the ANKH locus, including the promoter, consistently revealed the association. The bone traits tested are closely related to bone fragility suggesting a role for ANKH in osteoporosis.

Genetic signature consistent with selection against the CYP3A4*1B allele in non-African populations.

Cytochrome P450 3A enzymes (CYP3A) play a major role in the metabolism of steroid hormones, drugs and other chemicals, including many carcinogens. The individually variable CYP3A expression, which remains mostly unexplained, has been suggested to affect clinical phenotypes. We investigated the CYP3A locus in five ethnic groups. The degree of linkage disequilibrium (LD) differed among ethnic groups, but the most common alleles of the conserved LD regions were remarkably similar. Non-African haplotypes are few; for example, only four haplotypes account for 80% of common European Caucasian alleles. Large LD blocks of high frequencies were suggestive of selection. Accordingly, European Caucasian and Asian cohorts each contained a block of single nucleotide polymorphism (SNPs) with very high P excess values. The overlap between these blocks in these two groups contained only two of the investigated 26 SNPs and one of them was the CYP3A4*1B allele. The region centromeric of CYP3A4*1B exhibited high haplotype homozygosity in European Caucasians as opposed to African-Americans. CYP3A4*1B showed a moderate effect on CYP3A4 mRNA and protein expression, as well as on CYP3A activity assessed as Vmax of testosterone 6beta-hydroxylation in a liver bank. Our data are consistent with a functional relevance of CYP3A4*1B and with selection against this allele in non-African populations. The elimination of CYP3A4*1B involved different parts of the CYP3A locus in European Caucasians and Asians. Because CYP3A4 is involved in the vitamin D metabolism, rickets may have been the underlying selecting factor.

Polymorphisms in the genes encoding chemokine receptor 5, interleukin-10, and monocyte chemoattractant protein 1 contribute to cytomegalovirus reactivation and disease after allogeneic stem cell transplantation.

We analyzed 90 polymorphisms in 17 genes related to immune function for association with human cytomegalovirus (HCMV) reactivation and disease in patients after allogeneic stem cell transplantation. We found relevant markers (i) in CCR5 and IL-10 genes conferring a higher risk for the development of HCMV disease and (ii) in the MCP1 gene associated with HCMV reactivation. Testing of high-risk patients for the presence of these single-nucleotide polymorphisms might be useful for individualizing antiviral prophylaxis.