William H. Stone

Genetic Susceptibility to Thrombosis and Its Relationship to Physiological Risk Factors: The GAIT Study

Although there are a number of well-characterized genetic defects that lead to increased risk of thrombosis, little information is available on the relative importance of genetic factors in thrombosis risk in the general population. We performed a family-based study of the genetics of thrombosis in the Spanish population to assess the heritability of thrombosis and to identify the joint actions of genes on thrombosis risk and related quantitative hemostasis phenotypes. We examined 398 individuals in 21 extended pedigrees. Twelve pedigrees were ascertained through a proband with idiopathic thrombosis, and the remaining pedigrees were randomly ascertained. The heritability of thrombosis liability and the genetic correlations between thrombosis and each of the quantitative risk factors were estimated by means of a novel variance component method that used a multivariate threshold model. More than 60% of the variation in susceptibility to common thrombosis is attributable to genetic factors. Several quantitative risk factors exhibited significant genetic correlations with thrombosis, indicating that some of the genes that influence quantitative variation in these physiological correlates also influence the risk of thrombosis. Traits that exhibited significant genetic correlations with thrombosis included levels of several coagulation factors (factors VII, VIII, IX, XI, XII, and von Willebrand), tissue plasminogen activator, homocysteine, and the activated protein C ratio. This is the first study that quantifies the genetic component of susceptibility to common thrombosis. The high heritability of thrombosis risk and the significant genetic correlations between thrombosis and related risk factors suggest that the exploitation of correlated quantitative phenotypes will aid the search for susceptibility genes.

Genetic Determinants of Hemostasis Phenotypes in Spanish Families

BACKGROUND Recent studies have described genetic mutations that affect the risk of thrombosis as a result of abnormal levels of such hemostatic parameters as protein C, protein S, and the activated protein C resistance ratio. Although these mutations suggest that genes play a part in determining variability in some hemostasis-related phenotypes, the relative importance of genetic influences on these traits has not been evaluated. METHODS AND RESULTS The relative contributions of genetic and environmental influences to a panel of hemostasis-related phenotypes were assessed in a sample of 397 individuals in 21 extended pedigrees. The effects of measured covariates (sex, age, smoking, and exogenous sex hormones), genes, and environmental variables shared by members of a household were quantified for 27 hemostasis-related measures. All of these phenotypes showed significant genetic contributions, with the majority of heritabilities ranging between 22% and 55% of the residual phenotypic variance after correction for covariate effects. Activated protein C resistance ratio, activated partial thromboplastin time, and Factor XII showed the strongest heritabilities, with 71.3%, 83.0%, and 67.3%, respectively, of the residual phenotypic variation attributable to genetic effects. CONCLUSIONS These results clearly demonstrate the importance of genetic factors in determining variation in hemostasis-related phenotypes that are components of the coagulation and fibrinolysis pathways and that have been implicated in risk for thrombosis. The presence of such strong genetic effects suggests that it will be possible to localize previously unknown genes that influence quantitative variation in these hemostasis-related phenotypes that may contribute to risk for thrombosis.

Functional Effects of the ABO Locus Polymorphism on Plasma Levels of von Willebrand Factor, Factor VIII, and Activated Partial Thromboplastin Time

Lower levels of factor VIII and von Willebrand factor (vWF) have been reported in individuals with blood type O compared with individuals with other ABO blood types. However, this relationship has been demonstrated only by association studies and not by linkage studies. Also, it is not clear whether the ABO locus exerts a functional effect directly on these plasma factors or whether the ABO locus is in linkage disequilibrium with another locus that controls these factors. To distinguish between these 2 possibilities, we applied new statistical methods combining linkage and association tests in a pedigree-based sample. In contrast to most previous studies that used the ABO phenotypes, our study used the ABO genotypes, permitting us to distinguish AO from AA and BO from BB. Our results clearly showed significant linkage between the ABO locus and vWF antigen (P=0.00075). In addition, factor VIII coagulant activity and activated partial thromboplastin time showed suggestive linkage with the ABO locus (P=0.10 and P=0.13). All 3 plasma phenotypes showed significant differences between OO and non-OO genotypes. In addition, vWF antigen exhibited significant differences between O heterozygotes and non-OO homozygotes. This study is unique because it used a combined linkage and association test, which indicated that the ABO locus itself has a functional effect on these plasma phenotypes.

Immune response of a marsupial (Monodelphis domestica) to sheep red blood cells

A study of the humoral immune response of a marsupial, Monodelphis domestica, was performed using sheep red blood cells as the immunogen and a hemolytic titration as the assay. The primary response to a single intramuscular injection was similar to that observed in other mammalian species, except that the titers remained high for as long as 37 weeks after the initial injection. The secondary response was weaker than the primary response and diminished as early as 15 weeks after the initial injection (and only 11 weeks after the single booster injection). The hyperimmune response was similar to the secondary response, except that the titers remained consistent for up to 10 weeks and then fell to very low levels at 35 weeks. The data support the view that the primary humoral response of this marsupial is similar to that of eutherian mammals. However, the secondary and hyperimmune responses appear to be very weak, if present at all.

Cellular immune response of a marsupial, Monodelphis domestica.

Marsupials are interesting subjects for studies of comparative and developmental immunology because they separated from eutherian mammals over 100 million years ago and because the newborns are still in a fetal state. We studied cellular immunity in a fully pedigreed colony of the marsupial, M. domestica (commonly called the gray short-tailed opossum). Peripheral blood lymphocytes were separated on nylon wool columns into adherent cells bearing surface immunoglobulin (B cells) and nonadherent cells (T cells) recovered in the ratio of 1:3. Peripheral blood lymphocytes responded by proliferation to Con A and other mitogens. Nonadherent cells were responsive to Con A, but adherent cells were not. Peripheral blood lymphocytes were stimulated weakly or not at all by allogeneic or xenogeneic (mouse) cells in mixed lymphocyte culture. Despite the weak MLC response, which was not due to genetic homogeneity, allogeneic and xenogeneic tail skin grafts were rejected promptly. These data suggest that the cellular immune response of M. domestica is similar to that of eutherian mammals with the notable exception of weak MLC responses.

Individual Identification and Paternity Determination in Chimpanzees (Pan troglodytes) Using Human Short Tandem Repeat (STR) Markers

We studied 155 human short tandem repeat (STR) DNA markers in chimpanzees (Pan troglodytes) via the polymerase chain reaction (PCR). There is no difference in number of alleles per locus among STRs of different motif length (di-, tri-, or tetranucleotide repeats). We investigated 42 of the most informative STRs in greater detail using DNA isolated from a panel of 41 African-born, captive-housed chimpanzees. They reveal a wealth of genetic variability in chimpanzees, with an average of six alleles and 70.6% heterozygosity. The average paternity exclusion probability is 51.6%, and the best three STRs jointly provide >95% mean exclusion probability. Used in combination to define a multiple-locus genotype, the five most informative focal STRs can potentially uniquely identify every chimpanzee alive in the world. Although the subjects are of unknown geographical origin, homozygosity tests indicate little evidence for population subdivision. These markers represent the basis of a powerful battery of genetic tests, including individual identification, e.g., in poaching, paternity testing, or reconstruction of pedigrees among captive and wild chimpanzee breeding populations.

Cardiac Output, Central Volume and Dye Injection Curves in Traumatic Arteriovenous Fistulas in Man

Although arteriovenous fistulas are frequent in wartime, few measurements of cardiac output have been carried out by direct methods. Analysis of the curve obtained after rapid injection of T-1824 shows the feasibility of this method in patients with arteriovenous fistulas. Such patients have elevated cardiac indices, enlarged central blood volumes and acceleration of peak and manifest recirculation times. The abnormalities are corrected by surgery. Diagnostic use of the dye curve is suggested.

Comparison of biochemical polymorphisms and short tandem repeat (STR) DNA markers for paternity testing in rhesus monkeys (Macaca mulatta)

Genetic markers are indispensable for molecularand statistical genetic research involving nonhumanprimates. Genetic markers must be used to ascertainparentage and to confirm the accuracy of pedigreesbased solely on housing or demographic records;otherwise, the results of pedigree, linkage, orquantitative genetic analyses may be unreliable. Untilrecently, most genetic markers used in nonhuman primateswere plasma proteins or isozyme polymorphisms,which were required in large numbers, because levels ofgenetic variation revealed by these markers were ratherlow. We compared the newer, PCR-amplified shorttandem repeat markers (STRs) with a panel ofclassical biochemical polymorphic markers, for paternitydetermination among captive-bred rhesus monkeys. The STRmarkers exhibited an average genetic diversityof 64% and an expected paternity exclusionprobability of 0.443. Both of these were greater thanthe average 54.5% genetic diversity and 0.298 exclusionprobability exhibited by the biochemical markers.The STRs were much more efficient than thebiochemical markers for parentage determination, sincethey required only half the amount of genetic typingdata to resolve an average paternity case. Thus, theresults of applying these two classes ofgenetic markers in paternity tests were somewhatdifferent than expected on the basis of theoreticalexclusion probabilities. These differences were probablydue to inbreeding and other genetic differencesamong breeding colonies. Because they are moreinformative and provide rapid and efficient geneticdata, STRs are now the method of choice for parentagedetermination and pedigree corroboration among nonhumanprimates.

Classical genetic markers and DNA markers: a commensal marriage

In this paper, we present an overview of classical genetic markers in nonhuman primates and then contrast the discriminatory powers of these markers with DNA markers. We have restricted the scope of our discussion to genetic markers found in blood, since they have been studied most extensively over the past 30 years. For example, immunoglobulin allotypes, complement markers, transferrins, and other protein markers can be identified using serum or plasma. Lymphocytes carry the major histocompatibility complex (MHC) markers, which are very polymorphic in most nonhuman primates. Lymphocytes are also used as a source of DNA. Finally, red blood cells carry an enormous array of blood group as well as isozyme markers. Our discussion will be limited to three species: rhesus monkeys (Macaca mulatta), baboons (Papio hamadryas), and chimpanzees (Pan troglodytes), although the principles are applicable to all nonhuman primates.

Genetic research with nonhuman primates: serving the needs of mankind Symposium summary and future prospects

The wide array of papers delivered at this symposium, ranging from population genetics to molecular genetics, is convincing evidence that genetic research with nonhuman primates is in full bloom. In fact, progress has been quite remarkable considering that a significant number of pedigreed colonies of nonhuman primates have been available for less than 25 years, which is hardly enough time to raise 3 generations of chimpanzees, 5 generations of baboons or 6 generations of rhesus monkeys. Were it not for these pedigreed colonies, we would not have been privileged to have this assemblage of papers on behavior, social structure, predisposition to disease and management of breeding colonies. It is indeed exciting that preliminary evidence has been obtained for major genes that play a role in susceptibility to dyslipoproteinemias in baboons, and that monoclonal antibodies and DNA markers are helping us to understand cholesterol metabolism. And thanks to computers, we can now rank animals in a colony in terms of their useful genotypes as well as their productivity.One can not help but be impressed with the commonality of humans and nonhuman primates at the structural and functional levels. For example, the major histocompatibility systems and the maternal-fetal relationships are very similar. We heard that this similarity is even more striking at the chromosomal, biochemical and DNA levels. A provocative question yet to be answered is, “what accounts for the obvious differences between humans and nonhuman primates in view of these incredible similarities?”In light of these advances, this symposium was at the cutting edge of primate genetics and the papers published in this issue of Genetica are certain to be hallmarks in the literature.