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Genetic risk factors of venous thrombosis.

Venous thrombosis, whose main clinical presentations include deep vein thrombosis and pulmonary embolism, represents a major health problem worldwide. Numerous conditions are known to predispose to venous thrombosis and these conditions are commonly referred to as risk indicators or risk factors. Generally accepted or "classically" acquired risk factors for venous thromboembolism include advanced age, prolonged immobilisation, surgery, fractures, use of oral contraceptives and hormone replacement therapy, pregnancy, puerperium, cancer and antiphospholipid syndrome. In addition to these well-established risk factors for venous thrombosis, several lines of evidence that have emerged over the past few decades indicate a role of novel genetic risk factors, mainly related to the haemostatic system, in influencing thrombotic risk. The most significant breakthrough has been the confirmation of the concept that inherited hypercoagulable conditions are present in a large proportion of patients with venous thromboembolic disease. These include mutations in the genes that encode antithrombin, protein C and protein S, and the factor V Leiden and factor II G20210 A mutations. Moreover, plasmatic risk indicators, such as hyperhomocysteinemia and elevated concentrations of factors II, VIII, IX, XI and fibrinogen, have also been documented. This extensive list of genetic and acquired factors serves to illustrate that a single cause of venous thrombosis does not exist and that this condition should be considered as a complex or multifactorial trait. Complex traits can be understood by assuming an interaction between different mutations in candidate susceptibility genes. The risk that is associated with each genetic defect may be relatively low in isolation but the simultaneous presence of several mutations may dramatically increase disease susceptibility. Moreover, environmental factors may interact with one or more genetic variations to add further to the risk. The analysis of genetic risk factors and plasmatic factors, together with private life style and environmental factors, has contributed significantly to our understanding of the genetic predisposition to venous thrombosis.

Antithrombins↗

Overview of model-free methods for linkage analysis.

Methods of model-free linkage analysis do not require a detailed specification for the mode of inheritance of the trait locus being linked. Beginning with methods proposed by Penrose in the 1930s, which allowed detection of linkage only, these methods now allow one to use multipoint analysis both to locate trait genes and to estimate variance components that give information on the genetic mechanism underlying the trait. The newer methods can utilize data on multiple types of pairs of relatives other than just sibpairs, and they can detect multiple trait loci. In combination with special sampling schemes, these methods give hope that they may play a crucial role in unraveling the genetic etiology of multifactorial traits, regardless of whether epistatic interactions are present. The results of such analyses can guide the use of more powerful model-based linkage analyses.

Chromosome Mapping↗

The inheritance of hyperlipoproteinaemia with xanthomatosis. A study of 132 kindreds.

In a study of xanthomatosis kindreds in the county of Ostfold, Norway, 95 % of the living first degree relatives of the probands were investigated. Hyperlipoproteinaemia (lipid values above the 95th percentile) was present in 40.8 % of 554 first degree relatives of probands with xanthomatosis. The distribution curve was bimodal for cholesterol and LDL cholesterol concentrations, but not for triglyceride concentration within the different categories of families. The IIA lipoprotein pattern was the most frequent lipoprotein abnormality, in probands as well as in affected first degree relatives. However, IIB and IV lipoprotein patterns were also found in affected family members, irrespective of the pattern in the probands. About 93% of the xanthomatosis subjects had a lipoprotein disorder segregating as an autosomal dominant; the remaining 7 % were sporadic cases and/or had a multifactorially determined xanthomatosis. More sibs that offspring were affected; this was particularly pronounced for males with a IIA lipoprotein pattern. The genetic analysis gave no reason to suspect that hypercholesterolaemia with a IIA pattern is not the same disease as hypercholesterolaemia with a IIB pattern. However, a significant number of xanthomatosis patients had more than one type of hyperlipoproteinaemia. The frequency of the xanthomatosis trait was estimated to be 3.2/1000, and the ascertainment probability 0.6. The prevalence of familial hypercholesterolaemia with xanthomatosis was estimated to be 2.2/1000 and the multiple type hyperlipoproteinaemia with xanthomatosis had a frequency of 1.0/1000.

Chromosome Aberrations↗

Complex segregation analysis of thyroid autoantibodies: are they inherited as an autosomal dominant trait?

The presence of circulating autoantibodies (Abs) to the thyroid antigens thyroid peroxidase (TPO) and thyroglobulin (Tg) is a marker for autoimmune thyroid disease. Recent studies have suggested that the tendency to produce these Abs is inherited as an autosomal dominant characteristic. In order to confirm or refute these observations, we have carried out a complex segregation analysis using POINTER on Ab data in 86 unselected pedigrees (172 nuclear families). The overall prevalence of TPO Ab was 9.9% in men and 24.1% in women. Tg Ab was found in 11.0% of men and 23.5% of women. There was a marked tendency for both TPO Ab and Tg Ab to cluster in families and complex segregation analysis provided strong evidence for vertical transmission. However, it was not possible to distinguish between a single locus and a multifactorial model for either Ab. In the absence of strong evidence for a single locus, genetic linkage strategies are unlikely to be successful.

Adolescent↗

Heredity and the path to overweight and obesity.

Overweight and obesity are not homogeneous phenotypes as individuals differ in terms of the regional distribution of the excess weight or fat. Overweight and obesity are also complex multifactorial phenotypes influenced by both genetic and nongenetic determinants. Heritability of fat mass or percent body fat derived from underwater weighing measurement reaches about 25% of the age and gender adjusted phenotypic variance. Based on twin and parent-child data, it has been reported that the heritability of resting metabolic rate, thermic response to food, and energy cost of submaximal exercise, adjusted for the proper concomitants, is as high as 40%. The level of habitual physical activity also exhibits a significant heritability level on the order of about 25%. Experimental overfeeding with identical twins demonstrates that there are inherited differences in body weight and body composition response. The most important factor identified thus far to account for the individual differences in response to long-term overfeeding is a nutrient partitioning characteristic, namely the proportion of fat vs lean tissue gained. The high gainers are those storing energy primarily in the form of fat, while the low gainers are storing relatively more in the form of lean tissue.

Body Mass Index↗

The lidgap-Gates (lgGa) mutation for open eyelids at birth maps to mouse chromosome 13.

Complex nonadditive interactions between specific alleles at multiple loci may underlie many so-called multifactorial threshold birth defects. The open-eyelids-at-birth defect in mice is a good model for these defects, and an understanding of its genetic complexity begins with mapping the participating loci. The open-eyelids defect can be part of a syndrome or can occur with no other obvious phenotypic effects. Of the latter nonsyndromic forms, the lidgap series includes four extant mutations that are considered to be alleles based on complementation tests. All show genetic complexity in segregation ratios. None has been mapped previously. On the basis of a strategy of mapping the mutation with the simplest inheritance pattern first, we generated an extensive exclusion map for lidgap-Gates, lgGa, using morphological and protein polymorphisms. We then screened the non-excluded regions in a congenic strain, AEJ.LGG-lgGa, for SSLP markers and located the differential chromosome segment containing the lgGa locus in a region near the distal end of mouse Chromosome (Chr) 13. This linkage was confirmed and refined by typing SSLPs in 64 F2 and 74 BC1 progeny of a cross of LGG/Bc (lgGa/lgGa) to SWV/Bc. The lgGa mutation maps to a 1- to 2-cM region between D13Mit76 and D13Mit53. Integrin alpha 1 and integrin alpha 2, which map to the same general region, are possible candidate loci, based on their embryonic expression and cellular function. Evidence is also presented for a common unlinked recessive suppressor of the open eyelids trait caused by lgGa.

Animals↗

Serologic studies in a family with heterozygous C2 deficiency.

Twelve family members of a patient with systemic lupus erythematosus (SLE) and heterozygous deficiency of the second component of complement (C2) were studied. Histocompatibility (HLA) typing was determined for A, B, and DR and MB antigens. Serum samples were tested for a variety of antinuclear antibodies (ANA), lymphocytotoxic antibodies and rheumatoid factors, and C2 levels were determined by hemolytic titration. Inheritance of C2D, the gene coding for C2, was limited to the haplotype HLA-A25, B18, DR2. Low but significant titers of ANA, rheumatoid arthritis nuclear antigen (RANA) and/or rheumatoid factors were found in eight of the nine adult family members without association with HLA haplotype. The sister of the proband had persistently strongly positive LE cell preparations for more than a decade and had joint pains while taking sulfa drugs. The son of the proband had leukemia. All other family members were healthy. We conclude that the increased incidence of rheumatic disease in persons with C2D deficiency is multifactorial and requires environmental factors or other hereditary factors unrelated to the HLA-A25, B18, DR2 haplotype. The C2D gene is clearly not associated with positive ANA tests or immunoprecipitins to RANA.

Adult↗

Genetics of nonsyndromic cleft lip with or without cleft palate: is there a Mendelian sub-entity?

The mode of inheritance of nonsyndromic cleft lip with or without cleft palate (NSCLP) is still a matter of dispute. We performed segregation analysis on three data sets of families ascertained through an affected child with NSCLP. The first two data sets were selected in France and were pooled for a global analysis. No major gene effect could be evidenced in spite of a very large number of families (666 pedigrees including 719 nuclear families). The third data set was British and consisted of three-generation families including the offspring of probands. A major gene effect, as well as a strong residual multifactorial component, were highly significant and we could show that this evidence almost entirely came from the information on probands' offspring. We conclude that a mixture of monogenic and of multifactorial cases is probably the best explanation for the observations made in this study. Analyses performed in pedigrees with multiple cases closely related might allow reducing heterogeneity and help identifying those Mendelian sub-entities.

Child↗

Hypercoagulable states.

A hypercoagulable state is an enhanced tendency to form venous or arterial thrombi. In 1845, Virchow postulated three factors responsible for thrombosis that remain relevant today: alterations of the blood (hypercoagulability); changes in vessel wall (vascular injury); and impairment of blood flow (stasis). An increased understanding of the molecular basis of thrombosis has been aided by the identification of individuals with specific inherited defects in the natural anticoagulation system. These primary hypercoagulable states include antithrombin III, protein C and protein S deficiencies, dysfibrinogenemias, plasminogen deficiency, and decreased plasminogen activator activity. Individuals with thrombosis at an early age, a family history of thromboembolic disease, unusual sites of thrombosis, or recurrent thrombosis without apparent cause should be evaluated for a primary hypercoagulable defect. The majority of patients do not have a recognizable specific defect. However, there are a variety of underlying conditions or diseases that are associated with an increased risk for thrombosis. The etiologies of secondary hypercoagulable states are often unclear and may be multifactorial. Treatment of these inciting conditions or diseases may decrease the thrombotic tendency.

Blood Coagulation Factors↗

Mapping a new suggestive gene locus for autosomal dominant nephrolithiasis to chromosome 9q33.2-q34.2 by total genome search for linkage.

BACKGROUND: Nephrolithiasis is a complex, multifactorial disease resulting from genetic and environmental interaction. The pathogenesis of nephrolithiasis is far from being understood. So far, no gene locus for autosomal dominant nephrolithiasis only has been described. We here identified a new suggestive gene locus for autosomal dominant nephrolithiasis by a genome-wide search for linkage in a Spanish kindred with nephrolithiasis. METHODS: Clinical data, blood and urine samples of 18 individuals from a Spanish kindred with nephrolithiasis were collected. We performed a genome-wide search for linkage using 380 polymorphic microsatellite markers. RESULTS: Nephrolithiasis segregated in this Spanish kindred in a pattern compatible with autosomal dominant inheritance. The total genome search yielded the highest two-point LOD score of Z(max) = 1.99 (theta = 0) for marker D9S159 on chromosome 9q33.2-q34.2. Multipoint analysis of 24 polymorphic markers used for further fine mapping resulted in a LOD score of Z(max) = 2.7 (theta = 0) for markers D9S1881-D9S164, thereby identifying a new gene locus for autosomal dominant nephrolithiasis (NPL1). Two recombination events define D9S1850 as the centromeric flanking marker and D9S1818 as the telomeric flanking marker, restricting the NPL1 locus to a 14 Mb interval. CONCLUSION: We here identified a new suggestive gene locus (NPL1) for autosomal dominant nephrolithiasis. It is localized on chromosome 9q33.2-q34.2. The identification of the responsible gene will provide new insights into the molecular basis of nephrolithiasis.

Aged↗

[An analysis of the prevalence of isolated dental anomalies and of those associated with hereditary syndromes: a model for evaluating the genetic control of the dentition characteristics].

Tooth ontogenesis, morphogenesis, and eruption are under a multifactorial (genetic, epigenetic, environmental) control. The aim of this study has been a genetic appraisal of tooth developmental characteristics by means of the prevalence and patterns of association of tooth anomalies in a large sample of hereditary syndromes. MATERIALS AND METHODS. A sample of 169 hereditary syndromes exhibiting tooth abnormalities was collected from the literature: original articles were controlled in order to achieve uniformity of judgement about the definition of the dental defects. Tooth anomalies were classified according to anatomoclinical criteria: number (hypodontia/hyperdontia), shape, position, structure (enamel/dentin/cementum), size (micro-/macrodontism), eruption (precocious/delayed including unerupted teeth). Prevalence data were calculated for: 1) modes of syndrome inheritance; 2) syndromes exhibiting a single dental anomaly vs. syndromes exhibiting associated tooth abnormalities; 3) different types of tooth abnormalities; 4) isolated and associated tooth abnormalities.

Abnormalities, Multiple↗

Velo-cardio-facial syndrome and DiGeorge sequence with meningomyelocele and deletions of the 22q11 region.

Approximately 5% of children with neural tube defects (NTDs) have a congenital heart defect and/or cleft lip and palate. The cause of isolated meningomyelocele, congenital heart defects, or cleft lip and palate has been largely thought to be multifactorial. However, chromosomal, teratogenic, and single gene causes of combinations of NTDs with congenital heart defects and/or cleft lip and palate have been reported. We report on 3 patients with meningomyelocele, congenital heart defects, and 22q11 deletions. Two of the children had the clinical diagnosis of velo-cardio-facial syndrome (VCFS); both also have bifid uvula. The third child had DiGeorge sequence (DGS). The association of NTDs with 22q11 deletions has not been reported previously. An accurate diagnosis of the 22q11 deletion is critical as this micro-deletion and its associated clinical problems is transmitted as an autosomal dominant trait due to the inheritance of the deletion-bearing chromosome. We recommend that all children with NTDs and congenital heart defects, with or without cleft palate, have cytogenetic and molecular studies performed to detect 22q11 deletions.

Adult↗

Power of multifactor dimensionality reduction for detecting gene-gene interactions in the presence of genotyping error, missing data, phenocopy, and genetic heterogeneity.

The identification and characterization of genes that influence the risk of common, complex multifactorial diseases, primarily through interactions with other genes and other environmental factors, remains a statistical and computational challenge in genetic epidemiology. This challenge is partly due to the limitations of parametric statistical methods for detecting genetic effects that are dependent solely or partially on interactions with other genes and environmental exposures. We previously introduced multifactor dimensionality reduction (MDR) as a method for reducing the dimensionality of multilocus genotype information to improve the identification of polymorphism combinations associated with disease risk. The MDR approach is nonparametric (i.e., no hypothesis about the value of a statistical parameter is made), is model-free (i.e., assumes no particular inheritance model), and is directly applicable to case-control and discordant sib-pair study designs. Both empirical and theoretical studies suggest that MDR has excellent power for identifying high-order gene-gene interactions. However, the power of MDR for identifying gene-gene interactions in the presence of common sources of noise is not currently known. The goal of this study was to evaluate the power of MDR for identifying gene-gene interactions in the presence of noise due to genotyping error, missing data, phenocopy, and genetic or locus heterogeneity. Using simulated data, we show that MDR has high power to identify gene-gene interactions in the presence of 5% genotyping error, 5% missing data, or a combination of both. However, MDR has reduced power for some models in the presence of 50% phenocopy, and very limited power in the presence of 50% genetic heterogeneity. Extending MDR to address genetic heterogeneity should be a priority for the continued methodological development of this new approach.

Algorithms↗

A new model for the resolution of cultural and biological inheritance in the presence of temporal trends: application to systolic blood pressure.

A contemporary path model for the resolution of cultural and biological inheritance is extended to incorporate temporal variation in family resemblance. Specifically, the genetic and environmental effects, like all other parameters of the model, are allowed to vary over an individual's age according to some specific mathematical functions. In the computer program BETREND a library of such functions is incorporated. Data on systolic blood pressure in 542 Japanese-American nuclear families were analyzed. This new methodology detected significant temporal variation in cultural inheritance, a result that was not found previously by using static models which could only distinguish between adult and childhood heritabilities. Cultural heritability, estimated to be 10% at birth, increases to a maximum of 28% at age 36, at which time it declines until it eventually reaches 10% at age 49. Although not statistically significant, there was some evidence for temporal trends in genetic heritability as well. Ignoring trends, the genetic heritability was estimated as .30. On the other hand, trends in sibling environment were clearly nonsignificant. This model provides an objective method of testing the significance of temporal trends in familial resemblance by using multifactorial models, of resolving varying gene expression and transient environmental effects as possible sources of generating the observed temporal variation, and of estimating continuous changes in heritability with age.

Adolescent↗

Role of the duplicated CCAAT box region in gamma-globin gene regulation and hereditary persistence of fetal haemoglobin.

Hereditary persistence of fetal haemoglobin (HPFH) is a clinically important condition in which a change in the developmental specificity of the gamma-globin genes results in varying levels of expression of fetal haemoglobin in the adult. The condition is benign and can significantly alleviate the symptoms of thalassaemia or sickle cell anaemia when co-inherited with these disorders. We have examined structure-function relationships in the -117 HPFH gamma promoter by analysing the effect of mutating specific promoter elements on the functioning of the wild-type and HPFH promoters. We find that CCAAT box mutants dramatically affect expression from the HPFH promoter in adult blood but have little effect on embryonic/fetal expression from the wild-type promoter. Our results suggest that there are substantial differences in the structure of the wild-type gamma promoter expressed early in development and the adult HPFH promoter. Together with previous results, this suggests that gamma silencing is a complex multifactorial phenomenon rather than being the result of a simple repressor binding to the promoter. We present a model for gamma-globin gene silencing that has significant implications for attempts to reactivate the gamma promoters in human adults by pharmacological means.

Animals↗

Application of polygenic threshold models in the etiology of affective disorders.

Multiple studies show that familial transmission of affective disorders does not conform to the classical principles of Mendelian inheritance. With the purpose of testing polygenic threshold models of inheritance of affective disorders, a study was carried out on 1184 probands with affective disorders with secondary cases in their families (siblings and offspring). Nonparametric analysis (Chi square test) indicates that there is no statistically significant difference between the observed and expected frequencies of secondary cases, when the probands are divided into two subgroups--unipolar and bipolar. It is proved that the two forms have common etiologic factors and the clinical differences between them can be attributed to the threshold gene effects. The hypothesis that bipolar and unipolar disorders are respectively severe and mild forms of the same disorder and that the two-threshold multifactorial polygenic model most adequately predicts the familial transmission of affective disorders is accepted.

Bipolar Disorder↗

Etiology, pathogenesis and prevention of neural tube defects.

Spina bifida, anencephaly, and encephalocele are commonly grouped together and termed neural tube defects (NTD). Failure of closure of the neural tube during development results in anencephaly or spina bifida aperta but encephaloceles are possibly post-closure defects. NTD are associated with a number of other central nervous system (CNS) and non-neural malformations. Racial, geographic and seasonal variations seem to affect their incidence. Etiology of NTD is unknown. Most of the non-syndromic NTD are of multifactorial origin. Recent in vitro and in vivo studies have highlighted the molecular mechanisms of neurulation in vertebrates but the morphologic development of human neural tube is poorly understood. A multisite closure theory, extrapolated directly from mouse experiments highlighted the clinical relevance of closure mechanisms to human NTD. Animal models, such as circle tail, curly tail, loop tail, shrm and numerous knockouts provide some insight into the mechanisms of NTD. Also available in the literature are a plethora of chemically induced preclosure and a few post-closure models of NTD, which highlight the fact that CNS malformations are of hetergeneitic nature. No Mendelian pattern of inheritance has been reported. Association with single gene defects, enhanced recurrence risk among siblings, and a higher frequency in twins than in singletons indicate the presence of a strong genetic contribution to the etiology of NTD. Non-availability of families with a significant number of NTD cases makes research into genetic causation of NTD difficult. Case reports and epidemiologic studies have implicated a number of chemicals, widely differing therapeutic drugs, environmental contaminants, pollutants, infectious agents, and solvents. Maternal hyperthermia, use of valproate by epileptic women during pregnancy, deficiency and excess of certain nutrients and chronic maternal diseases (e.g. diabetes mellitus) are reported to cause a manifold increase in the incidence of NTD. A host of suspected teratogens are also available in the literature. The UK and Hungarian studies showed that periconceptional supplementation of women with folate (FA) reduces significantly both the first occurrence and recurrence of NTD in the offspring. This led to mandatory periconceptional FA supplementation in a number of countries. Encouraged by the results of clinical studies, numerous laboratory investigations focused on the genes involved in the FA, vitamin B12 and homocysteine metabolism during neural tube development. As of today no clinical or experimental study has provided unequivocal evidence for a definitive role for any of these genes in the causation of NTD suggesting that a multitude of genes, growth factors and receptors interact in controlling neural tube development by yet unknown mechanisms. Future studies must address issues of gene-gene, gene-nutrient and gene-environment interactions in the pathogenesis of NTD.

Anencephaly↗

[Multifactorial etiology of obesity: nutritional and central aspects].

World-wide obesity and its effects are public health problems. Research on way of life and eating habits give some indications of etiological factors. Breast feeding and quantity of proteins intake in formulas are factors influencing the risks of obesity later on in life. Research undertaken by Rolland Cachera shows us the importance of the curve of BMI and how the obesity rebound can be predictive of obesity in later years allowing early decisions of weight control. Energy intake and energy expenditure are regulated by the central nervous system. It is a complex mechanism of afferent and efferent systems through the hypothalamus. The inverse effects of ghreline and of leptine on energy balance are more and more studied and cases of precocious obesity are explained by the identification of rare forms of monogenic obesity linked to the metabolism of leptine. The importance of inherited genes has a role and genetic predisposition is a reality. This new approach allows a clinical, etiological and, in the future, probably therapeutic attitude in case of severe precocious obesity.

Body Mass Index↗