Genome-wide SNP association: identification of susceptibility alleles for osteoarthritis.

The successful identification of genes involved in common human disorders is dependent upon availability of informative sample sets, validated marker panels, a high-throughput scoring technology, and a strategy for combining these resources. We have developed a universal platform based on mass spectrometry (MassARRAY) for analyzing nucleic acids with high precision and accuracy. To fuel this technology we have generated more than 100,000 validated assays for single nucleotide polymorphisms (SNPs) covering virtually all known and predicted human genes, and a large DNA sample bank from more than 50,000 consented diseased (case) and healthy (control) individuals. Taking advantage of MassARRAY's capability for quantitative analysis of nucleic acids, allele frequencies are estimated in sample pools containing large numbers of individual DNAs. Comparing frequencies between case and control pools as a first-pass filtering step is a tremendous advantage in throughput and cost over individual genotyping. We have employed this approach in numerous genome-wide association studies to identify genes implicated in common complex diseases, including osteoarthritis (OA). Access to additional patient samples through collaborations allows us to conduct replication studies that validate true disease genes. These discoveries will expand our understanding of genetic disease predisposition, and our capabilities for early diagnosis and improved therapeutic approaches.

Linkage and potential association of obesity-related phenotypes with two genes on chromosome 12q24 in a female dizygous twin cohort.

Obesity is a multifactorial disorder with a complex phenotype. It is a significant risk factor for diabetes and hypertension. We assessed obesity-related traits in a large cohort of twins and performed a genome-wide linkage scan and positional candidate analysis to identify genes that play a role in regulating fat mass and distribution in women. Dizygous female twin pairs from 1,094 pedigrees were studied (mean age 47.0+/-11.5 years (range 18-79 years)). Nonparametric multipoint linkage analyses showed linkage for central fat mass to 12q24 (141 cM) with LOD 2.2 and body mass index to 8q11 (67 cM) with LOD 1.3, supporting previously established linkage data. Novel areas of suggestive linkage were for total fat percentage at 6q12 (LOD 2.4) and for total lean mass at 2q37 (LOD 2.4). Data from follow-up fine mapping in an expanded cohort of 1243 twin pairs reinforced the linkage for central fat mass to 12q24 (LOD 2.6; 143 cM) and narrowed the -1 LOD support interval to 22 cM. In all, 45 single-nucleotide polymorphisms (SNPs) from 26 positional candidate genes within the 12q24 interval were then tested for association in a cohort of 1102 twins. Single-point Monks-Kaplan analysis provided evidence of association between central fat mass and SNPs in two genes - PLA2G1B (P = 0.0067) and P2RX4 (P = 0.017). These data provide replication and refinement of the 12q24 obesity locus and suggest that genes involved in phospholipase and purinoreceptor pathways may regulate fat accumulation and distribution.

Skeletal muscle magnesium content is correlated with plasma glucose concentration in patients with essential hypertension treated with lisinopril or bendrofluazide.

The association between change in glucose metabolism and change in skeletal muscle magnesium (Mg) concentration induced by antihypertensive treatment was evaluated in 37 patients with essential hypertension randomly treated with either lisinopril or bendrofluazide. Before and after 6 months of treatment, skeletal muscle biopsies were performed, glucose tolerance was determined by oral (OGTT) and intravenous glucose tolerance tests (IVGTT), and insulin sensitivity was assessed by the hyperinsulinemic euglycemic clamp technique. An inverse relationship was found between the treatment-induced change in fasting plasma glucose concentration and change in skeletal muscle Mg concentration (r = -0.39, P < .05). However, there was no significant correlation between skeletal muscle Mg content and either insulin sensitivity measured by the hyperinsulinemic euglycemic clamp test or glucose tolerance evaluated by IVGTT and OGTT. In conclusion, an increased circulating glucose concentration was correlated with a decreased Mg concentration in skeletal muscle during antihypertensive treatment. However, the Mg concentration in skeletal muscle did not significantly predict the insulin sensitivity or glucose tolerance.