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Results for “Multifactorial Inheritance”

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PubMed1996

An autosomal screen for genes that predispose to celiac disease in the western counties of Ireland.

Celiac disease is a strongly heritable gastrointestinal illness that is an especially important model of the genetically complex multifactorial immune mediated diseases. The HLA component of celiac disease (a specific HLA-DQ heterodimer)is largely established and is relatively uncomplicated, and the environmental component (gluten and related grain storage proteins in the diet) is remarkably well understood. Previous family studies of celiac disease suggested that there is at least one important non-HLA locus. This locus may be a stronger genetic factor than HLA, and it apparently has a recessive mode of inheritance. We used a three step genome screening protocol to identify loci that contribute to celiac disease in the western counties of ireland, a region with the highest prevalence of celiac disease in the world. The most significant of several possible non-HLA loci that we found was on chromosome 6p about 30 cM telomeric from HLA. It has a multipoint maximum lod score of 4.66 (compared with 4.44 for HLA-DQ) and appears to have a recessive mode of inheritance. Our study localizes and provides strong evidence for linkage of at least one non-HLA locus to celiac disease and may serve as a prototype for an efficient approach to screening the human genome for loci that contribute to complex diseases.

Adolescent↗

PubMed1997

Evidence that genetic susceptibility to Mycobacterium tuberculosis in a Brazilian population is under oligogenic control: linkage study of the candidate genes NRAMP1 and TNFA.

SETTING: A study of multicase tuberculosis pedigrees from Northern Brazil. OBJECTIVE: To determine the model of inheritance for genetic susceptibility to tuberculosis, and to test the hypothesis that TNFA and NRAMP1 are candidate susceptibility genes. DESIGN: The study sample included 98 pedigrees, 704 individuals and 205 nuclear families. Segregation analyses were performed using the programs POINTER and COMDS. Combined segregation and linkage analysis was carried out within COMDS. Non-parametric linkage analyses were performed using BETA. RESULTS: A sporadic model for disease distribution in families was strongly rejected, as were polygenic and multifactorial models. A codominant single gene model provided the best fit (P < 0.001) to the data using POINTER. COMDS extended the analysis to compare single-gene and two-gene models. A general two-locus model for disease control was marginally favoured (0.01 < P < 0.05) over the codominant single-gene model. No evidence was found for linkage between susceptibility to disease per se and the TNF gene cluster. Weak linkage was observed using COMDS for genes (IL8RB, P = 0.039; D2S1471, P = 0.025) tightly linked (< 150 kb) to NRAMP1, but not for NRAMP1 itself. CONCLUSIONS: Tuberculosis susceptibility in this region of Brazil is under oligogenic control. Although a minor role for TNFA and NRAMP1 cannot be excluded, our data suggest that neither is a major gene involved in this oligogenic control.

Adolescent↗

PubMed1999

Schizophrenia: an epigenetic puzzle?

Developments in molecular biology over the past three decades have led to an increasing awareness of the importance of epigenetic phenomena in a variety of genome functions. Epigenetic aspects of complex multifactorial diseases including schizophrenia, however, have not been investigated sufficiently. Various facets of epigenetics are reevaluated through their putative relevance to four theories of schizophrenia: neurodevelopmental, dopamine dysfunction, viral, and genetic anticipation with unstable DNA. The heuristic value of the epigenetic model of schizophrenia arises from the possibility of integration of a wide variety of empirical data into a new theoretical framework. It can be hypothesized that in addition to pathological effects of DNA structural mutations and environmental factors, inherited and acquired epigenetic defects, or epimutations, may be of etiological importance in schizophrenia. In addition, the epigenetic model may lead to experiments investigating the molecular substrates of genetic-environmental interactions.

Dopamine↗

PubMed1994

Family studies of non-insulin-dependent diabetes mellitus in South Indians.

Though a genetic basis for non-insulin-dependent diabetes mellitus (NIDDM) is clear, the likely mode of inheritance is not known. The segregation of NIDDM was studied in 64 nuclear South Indian pedigrees (449 individuals) ascertained through an affected proband having both parents and more than 1 sibling alive and available for oral glucose tolerance testing. A high proportion of parents were found to be of abnormal glucose tolerance [89 of 128 (70%) diabetic and 11 of 128 (9%) impaired]. Complex segregation analysis was performed using (1) POINTER which implements the mixed model and distinguishes major gene, multifactorial and non-transmitted environmental contributions to affection and (2) COMDS which implements an oligogenic model with major gene, modifier gene and environmental contributions to a) affection and b) diathesis (an ordered polychotomy amongst non-affected family members, based on 2-h plasma glucose level). Using POINTER, there was no formal support for a major gene and the most parsimonious solutions were achieved with multifactorial models. Using COMDS, we found i) significant improvements in models when information on glucose levels in nondiabetic family members (diathesis) was included, ii) support for segregation of a diallelic gene as well as background familial resemblance, and iii) under the best-supported model, this diallelic locus featured incomplete dominance (d = 0.8) and a disease-predisposing allele frequency of 14%. In South Indians, segregation of NIDDM is inadequately described by simple major gene models: more complex models provide more satisfactory descriptions. This finding, if applicable in other populations, has important implications for the search for diabetes-susceptibility genes.

Blood Glucose↗

PubMed1995

Migraine and concomitant symptoms among 8167 adult twin pairs.

We studied the inheritance of migraine and concomitant symptoms among 2690 monozygotic (1524 female and 1166 male) pairs and 5497 dizygotic (2951 female and 2546 male) twin pairs. Our material consists of a population-based questionnaire study among Finnish twins in 1981. The definition of migraine is based on a questionnaire method. Concordance was assessed using probandwise concordance rates and tetrachoric correlations for monozygotic (MZ) and dizygotic (DZ) twin pairs. For estimating the contribution of genetic factors to the susceptibility of migraine, a polygenic multifactorial model was used. Structural equation models were applied for estimating variance components and to compare different genetic models. Nearly one-half (40% to 50%) of the liability to migraine is attributable to genetic factors. In all structural analyses, the model with both additive genetic and unshared environmental component had the best goodness-of-fit value. The genetic component varied between 34% to 51% in different migraine types. There were no remarkable differences between sexes except in the effects due to dominance, where the proportion was 26% for men and 14% for women. Concomitant symptoms among subjects within pairs concordant for headache had genetic effects varying from 56% (subjects with unilaterality) and 56% (subjects with visual symptoms) to 45% (persons with nausea and vomiting). The two threshold model of headache points to the continuum model of headache, and the thresholds represent different levels of severity of the pain. Our results emphasize a multifactorial and higher than previously reported genetic pattern in the etiology of migraine. Also unshared environmental factors play an important role.

Diseases in Twins↗

PubMed2006

Causal models in epidemiology: past inheritance and genetic future.

The eruption of genetic research presents a tremendous opportunity to epidemiologists to improve our ability to identify causes of ill health. Epidemiologists have enthusiastically embraced the new tools of genomics and proteomics to investigate gene-environment interactions. We argue that neither the full import nor limitations of such studies can be appreciated without clarifying underlying theoretical models of interaction, etiologic fraction, and the fundamental concept of causality. We therefore explore different models of causality in the epidemiology of disease arising out of genes, environments, and the interplay between environments and genes. We begin from Rothman's "pie" model of necessary and sufficient causes, and then discuss newer approaches, which provide additional insights into multifactorial causal processes. These include directed acyclic graphs and structural equation models. Caution is urged in the application of two essential and closely related concepts found in many studies: interaction (effect modification) and the etiologic or attributable fraction. We review these concepts and present four important limitations. 1. Interaction is a fundamental characteristic of any causal process involving a series of probabilistic steps, and not a second-order phenomenon identified after first accounting for "main effects". 2. Standard methods of assessing interaction do not adequately consider the life course, and the temporal dynamics through which an individual's sufficient cause is completed. Different individuals may be at different stages of development along the path to disease, but this is not usually measurable. Thus, for example, acquired susceptibility in children can be an important source of variation. 3. A distinction must be made between individual-based and population-level models. Most epidemiologic discussions of causality fail to make this distinction. 4. At the population level, there is additional uncertainty in quantifying interaction and assigning etiologic fractions to different necessary causes because of ignorance about the components of the sufficient cause.

Causality↗

PubMed1995

Genetic determinants of human hypertension.

Hypertension is a common trait of multifactorial determination imparting an increased risk of myocardial infarction, stroke, and end-stage renal disease. The primary determinants of hypertension, as well as the factors which determine specific morbid sequelae, remain unknown in the vast majority of subjects. Knowledge that a large fraction of the interindividual variation in this trait is genetically determined motivates the application of genetic approaches to the identification of these primary determinants. Success in this effort will afford insights into pathophysiology, permit preclinical identification of subjects with specific inherited susceptibility, and provide opportunities to tailor therapy to specific underlying abnormalities. To date, mutations in three genes have been implicated in the pathogenesis of human hypertension: mutations resulting in ectopic expression of aldosterone synthase enzymatic activity cause a mendelian form of hypertension known as glucocorticoid-remediable aldosteronism; mutations in the beta subunit of the amiloride-sensitive epithelial sodium channel cause constitutive activation of this channel and the mendelian form of hypertension known as Liddle syndrome; finally, common variants at the angiotensinogen locus have been implicated in the pathogenesis of essential hypertension in Caucasian subjects, although the nature of the functional variants and their mechanism of action remain uncertain. These early findings demonstrate the feasibility and utility of the application of genetic analysis to dissection of this trait.

Angiotensin II↗

PubMed1999

Mapping complex traits in diseases of the hair and skin.

The past decade has witnessed the ascendance of human genetics in modern medicine, and at the forefront of this movement is the identification of genetic factors underlying inherited diseases. The methods of genetic mapping and positional cloning have made the discovery of genes with alleles that cause simple Mendelian diseases commonplace. The elucidation of the genetic basis of such disorders has vitalized both human genetics and the entire medical community as the field has gained prominence. The fact remains, however, that diseases resulting from the action of alleles of a single gene comprise only a minor percentage of traits that are medically relevant to humanity. The majority of these are multifactorial "complex traits", which result from the aggregate contribution of an unknown number of genes interacting with each other and with the environment. The current challenge has become one of parlaying successes in the mapping of Mendelian diseases into the discovery of genes whose alleles predispose the development of a complex disease. In light of this challenge, this review summarizes the methods and addresses some of the central issues of complex trait mapping, while using examples from dermatologically-relevant complex traits such as psoriasis and alopecia. Additionally, current technical and theoretical advances as well as the potential impact of the Human Genome Project will be discussed.

Animals↗

PubMed1997

Alzheimer's disease and related dementias: prospects for treatment.

Alzheimer's disease (AD) represents a major challenge to healthcare costs and to academic and pharmaceutical research efforts. The approval in 1996 of the first of the second generation acetylcholinesterase inhibitors, donepexil (Aricept, Eisai/Pfizer), has offered new hope, albeit palliative, to AD sufferers and care givers. Research has continued on the genetics of AD with the identification of the autosomal dominant inheritance of genetic defects in one of three distinct genes coding for the presensilins 1 and 2 and amyloid precursor protein (APP). While driving an ever increasing research effort related to the production, deposition and clearance of Abeta peptides, these mutations account for less than 10% of the AD cases reported, indicating that other causative factors, both genetic and environmental, may contribute to the pathophysiology of AD unrelated to familial cohorts. A newly developed transgenic mouse model and a broader appreciation of the multifactorial nature of this complex, chronic disease state may help provide a more objective approach to understanding the disease per se as opposed to amyloid neurotoxicity specifically which may or may not be causative.

Journal Article↗

PubMed1996

Leber's hereditary optic neuropathy: historical and contemporary considerations.

Leber's hereditary optic neuropathy (LHON) is a distinct form of optic atrophy with a unique pattern of inheritance. The clinical reports of this disorder remain consistent with the original classic description made by Theodor Leber in 1871. Recent advances in the field of molecular genetics, however, have yielded insights into the etiological determinants underlying the clinical expression of LHON. Disease presentation, both ophthalmoscopically and clinically, are reviewed. Classic and atypical presentations are discussed with genetic testing as the definitive diagnostic measurement. Clinical and histopathological findings have led to the investigation of promising preclinical indicators of LHON symptomatology. Evidence of a multifactorial etiology has implicated a broad spectrum of potential intervention protocols. Teaming of the clinician and laboratory geneticist to identify those at risk is critical, not only for future clinical protocols, but to allow for immediate intervention when an effective therapy becomes available.

Diagnosis, Differential↗

PubMed1991

On the inheritance of abdominal aortic aneurysm.

To determine the mode of inheritance of abdominal aortic aneurysm, data on first-degree relatives of 91 probands were collected. Results of segregation analysis performed on these data are reported. Many models, including nongenetic and genetic models, were compared using likelihood methods. The nongenetic model was rejected; statistically significant evidence in favor of a genetic model was found. Among the many genetic models compared, the most parsimonious genetic model was that susceptibility to abdominal aortic aneurysm is determined by a recessive gene at an autosomal diallelic major locus. A multifactorial component in addition to the major locus does not increase the likelihood of the data significantly.

Adult↗

PubMed2001

Genetics of arterial prothrombotic risk states.

Coronary artery disease is a leading cause of death worldwide and the largest killer of men and women in the United States. The pathophysiology of myocardial infarction is multifactorial, and numerous physiologic systems converge to dictate the formation of the two fundamental lesions, thrombosis and atherosclerosis. In this review we address genetic aspects of arterial thrombosis and the key thrombotic factors that have been associated with the increased risk for its development. Specifically, we consider components of coagulation, fibrinolysis, and platelet adhesive receptors, and we review the genetic epidemiology and in vitro laboratory data regarding their risk for the acute coronary syndromes. In combination with traditional risk factor assessment, in the near future these inherited markers can be used to manage patients with vascular disease through a better utilization of invasive or expensive diagnostic testing, as well as pharmacologic intervention.

Blood Coagulation Factors↗

PubMed2003

How to model a complex trait. 1. General considerations and suggestions.

Usually, when complex traits are at issue, not only are the loci of the responsible genes a priori unknown; the same also holds for the mode of inheritance of the trait, and sometimes even for the phenotype definition. The term mode of inheritance relates to both the genetic mechanism, i.e., the number of loci implicated in the etiology of the disease, and the genotype-phenotype relation, which describes the influence of these loci on the trait. Having an idea of the genetic model can crucially facilitate the mapping process. This holds especially in the context of linkage analysis, where an appropriate parametric model or a suitable nonparametric allele sharing statistic may accordingly be selected. Here, we review the difficulties with parametric and nonparametric linkage analysis when applied to multifactorial diseases. We address the question why it is necessary to adequately model a genetically complex trait in a linkage study, and elucidate the steps to do so. Furthermore, we discuss the value of including unaffected individuals into the analysis, as well as of looking at larger pedigrees, both with parametric and nonparametric methods. Our considerations and suggestions aim at guiding researchers to genotyping individuals at a trait locus as accurately as possible.

Chromosome Mapping↗

PubMed2002

A cellular automata approach to detecting interactions among single-nucleotide polymorphisms in complex multifactorial diseases.

The identification and characterization of susceptibility genes for common complex multifactorial human diseases remains a statistical and computational challenge. Parametric statistical methods such as logistic regression are limited in their ability to identify genes whose effects are dependent solely or partially on interactions with other genes and environmental exposures. We introduce cellular automata (CA) as a novel computational approach for identifying combinations of single-nucleotide polymorphisms (SNPs) associated with clinical endpoints. This alternative 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. We demonstrate using simulated data that the approach has good power for identifying high-order nonlinear interactions (i.e. epistasis) among four SNPs in the absence of independent main effects.

Algorithms↗

PubMed2005

Laboratory detection of inherited thrombophilia: a historical perspective.

Considerable progress has been made in determining the molecular bases of inherited thrombophilia in the last 25 years. There are several genetic abnormalities that can be detected in the laboratory and are currently recognized to be unequivocally associated with an increased tendency to develop venous thrombosis. Testing for inherited and acquired causes of thrombophilia may make counseling more focused in ostensibly healthy members of thrombophilic families (i.e., those in which a measurable abnormality was identified in one or more asymptomatic persons). In other situations, including women who start taking oral contraceptives, become pregnant, or consider hormone replacement therapy, screening is generally not useful. It is hoped that because we currently have such simple and clinically useful global tests of hypocoagulability as the prothrombin time and activated partial thromboplastin time, it may soon become possible to measure multifactorial thrombophilia without resorting to the multiplicity of tests now necessary.

Blood Coagulation↗

PubMed2002

Waging war on physical inactivity: using modern molecular ammunition against an ancient enemy.

A hypothesis is presented based on a coalescence of anthropological estimations of Homo sapiens' phenotypes in the Late Paleolithic era 10,000 years ago, with Darwinian natural selection synergized with Neel's idea of the so-called thrifty gene. It is proposed that humans inherited genes that were evolved to support a physically active lifestyle. It is further postulated that physical inactivity in sedentary societies directly contributes to multiple chronic health disorders. Therefore, it is imperative to identify the underlying genetic and cellular/biochemical bases of why sedentary living produces chronic health conditions. This will allow society to improve its ability to effect beneficial lifestyle changes and hence improve the overall quality of living. To win the war against physical inactivity and the myriad of chronic health conditions produced because of physical inactivity, a multifactorial approach is needed, which includes successful preventive medicine, drug development, optimal target selection, and efficacious clinical therapy. All of these approaches require a thorough understanding of fundamental biology and how the dysregulated molecular circuitry caused by physical inactivity produces clinically overt disease. The purpose of this review is to summarize the vast armamentarium at our disposal in the form of the extensive scientific basis underlying how physical inactivity affects at least 20 of the most deadly chronic disorders. We hope that this information will provide readers with a starting point for developing additional strategies of their own in the ongoing war against inactivity-induced chronic health conditions.

Animals↗

PubMed1999

Inherited disorders of iron metabolism.

Recent molecular studies have resulted in the identification of genetic alterations underlying hereditary disorders of iron metabolism. One example is the discovery of the HFE gene that is mutated in patients suffering from hereditary hemochromatosis. This autosomal recessive disorder has an estimated carrier frequency that varies between 0.07 and 0.13, thus representing one of the most common genetically determined metabolic disorders. The identification of the hemochromatosis mutations has encouraged efforts to investigate other conditions with iron overload for a putative interaction with these genetic variants. Few data are already available suggesting, for example, that iron overload in patients with sporadic porphyria cutanea tarda is associated with mutations in the hereditary hemochromatosis gene. However, it is obvious that disorders of iron metabolism have a multifactorial pathogenesis, including environmental and genetic factors. Thus, many questions remain to be answered about whether a genetic predisposition exists for development of various iron-loading or iron-deficiency phenotypes. This review focuses on the most recent advances in the field of hereditary disorders of iron metabolism and discusses their potential implications for nephrologists.

Anemia↗

PubMed2001

Mouse models of blood pressure regulation and hypertension.

Human essential hypertension is recognized as a multifactorial disease involving many genes, but the causative genes have not yet been identified. For many years hypertension was studied primarily in the rat, but more recently several candidate genes for hypertension have been used to produce transgenic mice for gain of function and gene-targeted mice for loss of function studies. These genetically engineered mouse strains with hypertension or hypotension are providing insights into the mechanisms of blood pressure regulation. However, genetically engineered mice are used to study one gene at a time, and another complementary approach is needed for polygenic inheritance and gene interaction. The phenotype-driven approach to hypertension studies uses the natural variation among inbred strains and crosses to find quantitative trait loci. The four mouse crosses carried out so far have found several quantitative trait loci that are concordant with hypertension loci found in rats and humans.

Animals↗