Kelly L. Krass

Combined analysis of genome scans of dutch and finnish families reveals a susceptibility locus for high-density lipoprotein cholesterol on chromosome 16q

Several genomewide screens have been performed to identify novel loci predisposing to unfavorable serum lipid levels and coronary heart disease (CHD). We hypothesized that the accumulating data of these screens in different study populations could be combined to verify which of the identified loci truly harbor susceptibility genes. The power of this strategy has recently been demonstrated with other complex diseases, such as inflammatory bowel disease and asthma. We assessed the largely unknown genetic background of CHD by investigating the most common dyslipidemia predisposing to CHD, familial combined hyperlipidemia (FCHL), affecting 1%-2% of Western populations and 10%-20% of families with premature CHD. To be able to perform a combined data analysis, we unified the diagnostic criteria for FCHL and its component traits and combined the data from two genomewide scans performed in two populations, the Finns and the Dutch. As a result of our pooled data analysis, we identified three chromosomal regions, on chromosomes 2p25.1, 9p23, and 16q24.1, exceeding the statistical significance level of a LOD score >2.0. The 2p25.1 region was detected for the FCHL trait, and the 9p23 and 16q24.1 regions were detected for the low high-density lipoprotein cholesterol (HDL-C) trait. In addition, the previously recognized 1q21 region also obtained additional support in the other study sample, when the triglyceride trait was used. Analysis of the 16q24.1 region resulted in a statistically significant LOD score of 3.6 when the data from Finnish families with low HDL-C were included in the analysis. To search for the underlying gene in the 16q24.1 region, we investigated a novel functional and positional candidate gene, helix/forkhead transcription factor (FOXC2), by sequencing and by genotyping of two single-nucleotide polymorphisms in the families.

Genetic loci for diet-induced atherosclerotic lesions and plasma lipids in mice.

Genetic factors independent of those affecting plasma lipid levels are a major contributor to risk for atherosclerosis in humans, yet the basis for these is poorly understood. This study examined plasma lipids and diet-induced atherosclerosis in 16-month-old female mice of strains C56BL/6J and DBA/2J. Mice of the parental strains, from recombinant inbred strains derived from these (BXD RI), and F2 progeny were fed an atherogenic diet for 16 weeks, beginning at 1 year of age. This induced atherosclerotic lesion formation in both parental strains, accompanied by increased plasma LDL levels. However, individual BXD RI strains and the BXD F2 mice demonstrated a range of atherosclerotic lesion formation that was not or at best weakly correlated with plasma lipid levels. Quantitative trait locus (QTL) analysis of the BXD F2 mice identified a locus with significant linkage (lod 4.5) for aortic lesion size on Chromosome (Chr) 10 that was independent of plasma lipids. Other loci with suggestive or significant linkage for various plasma lipid measures were identified on Chr 2, 3, 4, 5, 6, 7, 11, and 17. In this intercross, the genes primarily influencing atherosclerosis are distinct from those controlling plasma lipid levels.

Locus for Elevated Apolipoprotein B Levels on Chromosome 1p31 in Families With Familial Combined Hyperlipidemia

Familial combined hyperlipidemia (FCH), a common cause of premature coronary artery disease, is genetically complex and poorly understood. Recently, a major locus on chromosome 1q21-23 exhibiting highly significant linkage was identified in Finnish FCH families by use of a parametric analysis. We now report highly significant evidence of linkage (maximum LOD score 3.8, recombination fraction 0) of an important FCH phenotype, elevated apolipoprotein B (apoB) levels, to a distinctly separate locus on chromosome 1p31 in Dutch pedigrees. ApoB is the major protein on very low density and low density lipoproteins, and elevated apoB levels have been used as a surrogate trait for FCH. Additional microsatellite markers in the 1p31 region were genotyped, and evidence of linkage improved (maximum LOD score 4.7) in a multipoint analysis of two markers in the peak region. The leptin receptor gene resides within this locus and is involved in obesity and insulin/glucose homeostasis. However, there was no evidence of an association between leptin receptor and apoB levels, raising the possibility that another gene on this chromosomal region contributes to elevated apoB levels in this Dutch population. This is one of the first loci identified for apoB levels in humans and is the second major locus implicated in the genetic etiology of FCH.

Genetic loci influencing natural variations in femoral bone morphometry in mice

This study identifies genetic loci affecting femoral bone length and width measures in mature mice. Sixteen month old female F2 progeny of a C57BL/6J and DBA/2J intercross were examined for femur length and width of the femoral head, intertrochanteric region and three locations of the diaphysis using digitized images of femur radiographs obtained in the anterior‐posterior and lateral projections. A genome wide linkage map was constructed using microsatellite markers at an average density of 20 cM, and quantitative trait locus analysis used to identify regions of the genome showing linkage with the traits measured. Femur length showed significant linkage with loci on proximal chromosome 3 (lod 6.1), and suggestive linkage with a locus on chromosome 14. A major locus on mid‐chromosome 7 controlled width of the diaphysis (lod 6.8). Other loci were identified on chromosomes 2 and 4. Width at the intertrochanteric region had suggestive linkage with loci on chromosomes 6 and 19. No loci were found with linkage for width of the femoral head. Candidate genes related to bone development or metabolism are present at most of these loci. These findings show that genetic regulation of femoral bone morphology is complex, and are consistent with the distinct biologic processes that control longitudinal and lateral growth of the femur.

Genetic characterization of the Dyscalc locus

Abstract. Calcification occurs frequently in the development of atherosclerotic lesions, and studies in mice have indicated a genetic contribution. We now show that one genetic factor contributing to aortic calcification is the Dyscalc locus, previously shown to contribute to myocardial calcification. Thus, the Dyscalc locus, on proximal mouse Chromosome (Chr) 7, segregated with vascular calcification in a large cross between susceptible strain DBA/2J and resistant strain C57BL/6J. Further evidence was observed by analysis of recombinant inbred strains derived from various susceptible and resistant parental strains. Myocardial and vascular calcifications are importantly influenced by multiple modifier loci as well as the Dyscalc gene, making fine mapping of Dyscalc difficult. In order to allow more detailed genetic and biochemical characterization of Dyscalc, we have identified congenic strains containing the Dyscalc locus from resistant strain C57BL/10 on the background of susceptible strain C3H/DiSnA. The congenic strains exhibit little or no myocardial or vascular calcification, unlike the background HcB C3H strain, and the calcification segregated as a Mendelian factor, allowing finer mapping of Dyscalc.

Vitamins at the heart of heart disease

Atherosclerosis is a chronic inflammatory disease of the large arteries that is the cause of heart disease and stroke. Although effective drugs for the treatment of atherosclerosis have been developed, including the cholesterol-lowering family of statins, it remains the leading cause of death in westernized countries. In fact, atherosclerosis is now supplanting infectious disease as the major cause of death worldwide due to the continued westernization of parts of the world. It is a disease of exceptional aetiological complexity, as more than a dozen important risk factors, both genetic and environmental, have been identified in epidemiological studies. It involves a host of cell types, including endothelial cells, monocytes, macrophages, smooth-muscle cells, lymphocytes and platelets, that participate in the initiation, growth and rupture of an atherosclerotic plaque. Atherosclerosis is a collection of twenty essays focusing on the role of oxidation and inflammation in the disease. The oxidative hypothesis proposes that oxidative processes, particularly those involving lipid oxidation, trigger inflammatory events and promote the formation of the cholesterolengorged macrophages that are a hallmark of the disease. Over the past decade, the belief that eating a diet low in cholesterol and saturated fats can largely prevent atherosclerosis has become quite popular. Studies have repeatedly shown that high intake of saturated fat is positively related to high mortality from coronary heart disease (CHD). How, then, do we explain the French paradox? France, notorious for its rich foods high in both cholesterol and saturated fatty acids, has an extremely low morbidity due to CHD. Multiple groups have explained this paradox by noting the increased anti-oxidants present in both wine and vegetables consumed regularly by the French. As suggested in Atherosclerosis, perhaps our ability to prevent and reverse oxidative events is more important than the sheer number of lipidrich particles present. Assuming that antioxidants are the key to healthy arteries, shouldn’t we all rush to our nearest vitamin retailer, and purchase large quantities of vitamin E and β-carotene? Despite supporting evidence from a variety of animal studies, the hypothesis remains controversial, as some large trials with antioxidants have yielded inconclusive evidence in humans. It is possible that the inability of natural and synthetic antioxidants to markedly slow or stop the progression of human atherosclerotic lesions is because oxidation is merely one of many causative factors, or simply that the administered antioxidants cannot provide the needed protection at the relevant sites, such as the vessel wall. Atherosclerosis takes a direct and indepth approach to addressing some important questions in atherogenesis. It provides a critical and up-to-date overview of data relating to oxidation, along with useful background information not found in research papers. The book includes an excellent chapter on the results of clinical trials involving antioxidants. It also contains some chapters addressing related aspects of atherogenesis that provide the reader with an understanding of the pathology of the disease. For example, a complete chapter is dedicated to each of the four main cell types involved in the atherogenic process. Although the book succeeds in exposing the cutting edge of a number of research issues in atherogenesis, its scope is limited because some important areas are omitted. In particular, genetic approaches in humans and animal models are only briefly mentioned. This seems curious, because population association studies with such genetic factors as serum paraoxonase provide some of the more compelling evidence of a link between oxidation and atherosclerosis in humans. There is also little discussion of the hundreds of transgenic mouse studies that have provided strong mechanistic information in vivo, including aspects relevant to oxidation and inflammation. The focus on biochemistry and cellular interactions seems to reflect the research emphasis of The Heart Research Institute, Sydney, where the book originates. A weakness of the book is the near absence of figures associated with complex passages of text. This lack of pictures is perhaps most notable in the introductory chapter on the pathogenesis of the disease, making Atherosclerosis less suitable for casual readers. With a heavy emphasis on basic research, this book will be of greatest value to investigators involved in cardiovascular research. After reading the book, we had a much better understanding of the current status of the oxidation hypothesis. Clearly there is a large quantity of supporting data, primarily from studies of tissue culture cells and animal models. However, the French paradox is still a paradox, and purchasing shares in a vitamin distribution company might still be a little premature. Kelly L. Krass and Aldons J. Lusis are at the Department of Microbiology, Immunology and Molecular Genetics, UCLA, Los Angeles, California 90095, USA e-mail: jlusis@mednet.ucla.edu