Genetic and environmental influences on premature death in adult adoptees

Genetic control and dynamics of the cellular immune response to the human T-cell leukaemia virus, HTLV-I

About 1% of people infected with the human T-cell leukaemia virus, type 1 (HTLV-I) develop a disabling chronic inflammatory disease of the central nervous system known as HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Patients with HAM/TSP have a vigorous immune response to HTLV-I, and it has been widely suggested that this immune response, particularly the HTLV-I-specific cytotoxic T-lymphocyte (CTL) response, causes the tissue damage that is seen in HAM/TSP. In this paper we summarize recent evidence that a strong CTL response to HTLV-I does in fact protect against HAM/TSP by reducing the proviral load of HTLV-I. We conclude that HTLV-I is persistently replicating at a high level, despite the relative constancy of its genome sequence. These results imply that antiretroviral drugs could reduce the risk of HAM/TSP by reducing the viral load, and that an effective anti-HTLV-I vaccine should elicit a strong CTL response to the virus. The dynamic nature of the infection also has implications for the epidemiology and the evolution of HTLV-I.

Interleukin-1 receptor antagonist gene polymorphism and coronary artery disease

BACKGROUND

Cytokine gene variations are contributory factors in inflammatory pathology. Allele frequencies of interleukin (IL)-1 cluster genes [IL-1A(-889), IL-1B(-511), IL-1B(+3953), IL-1RN Intron 2 VNTR] and tissue necrosis factor (TNF)-alpha gene [TNFA(-308)] were measured in healthy blood donors (healthy control subjects), patients with angiographically normal coronary arteries (patient control subjects), single-vessel coronary disease (SVD), and those with multivessel coronary disease (MVD).

METHODS AND RESULTS

Five hundred fifty-six patients attending for coronary angiography in Sheffield were studied: 130 patient control subjects, 98 SVD, and 328 MVD. Significant associations were tested in an independent population (London) of 350: 57 SVD, 191 MVD, and 102 control subjects. IL-1RN*2 frequency in Sheffield patient control subjects was the same as in 827 healthy control subjects. IL-1RN*2 was significantly overrepresented in Sheffield SVD patients (34% vs 23% in patient control subjects); IL-1RN*2 homozygotes in the SVD population (chi2 carriage=8.490, 1 df, P=0.0036). This effect was present though not quite significant in the London population (P=0. 0603). A summary trend test of the IL-1RN SVD genotype data for Sheffield and London showed a significant association with *2 (P=0. 0024). No significant effect of genotype at IL-1RN was observed in the Sheffield or London MVD populations. Genotype distribution analysis comparing the SVD and MVD populations at IL-1RN showed a highly significant trend (P=0.0007) with the use of pooled data. No significant associations were seen for the other polymorphisms.

CONCLUSIONS

IL-1RN*2 was significantly associated with SVD. A difference in genetic association between SVD and MVD was also apparent.

Differential association of common carotid intima-media thickness and carotid atherosclerotic plaques with parental history of premature death from coronary heart disease : the EVA study

Familial aggregation of coronary heart disease (CHD) has been reported in several studies. The specific underlying mechanisms and the relative contribution of atherosclerosis to the subsequent CHD events in subjects with family history are not well established. This study examined the association of parental history of premature death from CHD with ultrasound carotid measurements of atherosclerosis in a population of 1040 subjects aged 59 to 71 years. Ultrasound examination included measurements of intima-media thickness at the common carotid arteries (at sites free of plaques) and assessment of atherosclerotic plaques in the extracranial carotid arteries. Subjects who reported that 1 or both parents had sudden death or died of myocardial infarction before the age of 65 years were considered positive for parental history of premature death from CHD (n=53, 5.1%). The prevalence of atheromatous plaques was higher in subjects with history of premature death from CHD compared with those without history (41.5% versus 20.5%, P<0.001). Age- and sex-adjusted odds ratio of atheromatous plaques associated with parental history of premature death from CHD was 2.85 (95% confidence interval, 1.60 to 5.08; P<0.001). Multivariate adjustment for major known cardiovascular risk factors did not markedly alter the results (odds ratio, 2.70; P<0.002). In contrast, common carotid intima-media thickness was not associated with parental history of premature death from CHD (0.66+/-0.11 versus 0.66+/-0.12 mm, P=0.76). These findings were observed in both men and women. In conclusion, parental history of premature death from CHD is strongly associated with carotid plaques. Familial transmission of CHD risk does not seem to be specifically mediated by arterial wall thickening measured at sites free of plaques.

The immunogenetics of human infectious diseases

Twin and adoptee studies have indicated that host genetic factors are major determinants of susceptibility to infectious disease in humans. Twin studies have also found high heritabilities for many humoral and cellular immune responses to pathogen antigens, with most of the genetic component mapping outside of the major histocompatibility complex. Candidate gene studies have implicated several immunogenetic polymorphisms in human infectious diseases. HLA variation has been associated with susceptibility or resistance to malaria, tuberculosis, leprosy, AIDS, and hepatitis virus persistence. Variation in the tumor necrosis factor gene promoter has also been associated with several infectious diseases. Chemokine receptor polymorphism affects both susceptibility ot HIV-1 infection and the rate of progression to AIDS. Inactivating mutations of the gamma-interferon receptor lead to increased susceptibility to typical mycobacteria and disseminated BCG infection in homozygous children. The active form of vitamin D has immunomodulatory effects, and allelic variants of the vitamin D receptor appear to be associated with differential susceptibility to several infectious diseases. NRAMP1, a macrophage gene identified by positional cloning of its murine homologue, has been implicated in susceptibility to tuberculosis in Africans. Whole genome linkage analysis of multi-case families is now being used to map and identify new loci affecting susceptibility to infectious diseases. It is likely that susceptibility to most microorganisms is determined by a large number of polymorphic genes, and identification of these should provide insights into protective and pathogenic mechanisms in infectious diseases.

A methylenetetrahydrofolate reductase gene polymorphism in ischaemic stroke and in carotid artery stenosis

METHODS

A biallelic polymorphism of the methylenetretrahydrofolate reductase (MTHFR) gene, reported to influence the plasma level of homocysteine (Hcy), was investigated for a possible role in influencing the risk of ischaemic cerebrovascular disease (ICVD) and occlusive atherosclerosis in 126 patients with ischaemic stroke and 70 patients with internal carotid artery (ICA) stenosis.

RESULTS

Only minor differences were observed between different groups of patients and control subjects. Although 47% of ICA stenosis patients had increased plasma Hcy, the MTHFR genotype did not correlate with levels of either Hcy, folic acid or vitamin B12. In addition, the MTHFR genotype did not affect Hcy levels, even in the presence of low blood folate.

CONCLUSION

We conclude that this common MTHFR gene polymorphism does not exert a significant influence on the risk of developing ICVD or ICA stenosis, and does not cause the increased level of Hcy observed in ICA stenosis.

Cardiovascular risk factor profile in subjects with familial predisposition to myocardial infarction in Denmark

STUDY OBJECTIVES

To identify possible modifiable mediators of familial predisposition to myocardial infarction (MI) by assessing the risk factor profile in individuals without MI in relation to parental occurrence of MI.

DESIGN AND METHODS

Cross sectional survey of the general population. The odds of an adverse cardiovascular risk factor profile in subjects reporting parental occurrence of MI versus subjects not reporting parental occurrence were estimated by logistic regression models.

SETTING

The Copenhagen Centre for Prospective Population Studies, where subjects investigated in three Danish prospective population studies are integrated.

PARTICIPANTS

Subjects were 9306 females and 11,091 males aged 20-75 years with no history of MI. A total of 1370 subjects reported maternal MI and 2583 reported paternal MI.

MAIN RESULTS

Increased systolic and diastolic blood pressure, increased cholesterol level, low ratio between high density lipoprotein (HDL) and total cholesterol (TC), and heavy smoking, were more frequent in subjects with parental occurrence of MI than in controls irrespective of sex and age of the subjects. Maternal MI was more predictive for increased cholesterol and decreased HDL/ TC ratio than paternal MI, and the risk of an increased cholesterol level was higher in subjects aged 20-39 years than in older subjects. No differences in body mass index, triglycerides, and physical inactivity were observed.

CONCLUSIONS

Subjects free of previous MI who reported a parental occurrence of MI had an adverse cardiovascular risk factor profile regarding systolic and diastolic blood pressure, total cholesterol, the ratio between HDL and total cholesterol, and smoking. Thus, these modifiable risk factors may be mediators of the familial predisposition to MI.

How frailty models can be used for evaluating longevity limits: Taking advantage of an interdisciplinary approach

In this paper we discuss an approach to the analysis of mortality and longevity limits when survival data on related individuals with and without observed covariates are available. The approach combines the ideas of demography and survival analysis with methods of quantitative genetics and genetic epidemiology. It allows us to analyze the genetic structure of frailty in the Cox-type hazard model with random effects. We demonstrate the implementation of this strategy to survival data on Danish twins. We then evaluate the resulting lower bounds for biological limits of human longevity. Finally, we discuss the limitations of this approach and directions of further research.

Genetic influence on cytokine production and fatal meningococcal disease

BACKGROUND

To assess the genetic influence on cytokine production and its contribution to fatal outcome, we determined the capacity to produce tumour necrosis factor-alpha (TNF alpha) and interleukin-10 (IL-10) in families of patients who had had meningococcal disease.

METHODS

We studied 190 first-degree relatives of 61 patients with meningococcal disease; we also studied 26 monozygotic twins. Production of cytokines was determined during endotoxin stimulation of whole-blood samples ex-vivo. Heritability was estimated in a pedigree-based maximum-likelihood model. DNA was typed for the G to A transition polymorphisms at position -308 and -238 in the TNF gene promoter.

FINDINGS

Heritability in monozygotic twins was 0.60 for the production of TNF and 0.75 for the production of IL-10. Families with low TNF production had a tenfold increased risk for fatal outcome (OR 8.9, 95% CI 1.8-45), whereas high IL-10 production increased the risk 20-fold (19.5, 2.3-165). Families with both characteristics had the greatest risk. The transition polymorphisms in the TNF gene promoter were not associated with outcome.

INTERPRETATION

Genetic factors substantially influence production of cytokines. An innate anti-inflammatory cytokine profile may contribute to fatal meningococcal disease.

The association between human leucocyte antigens (HLA) and mortality in community residents aged 85 and older

OBJECTIVE

The association between Human Leucocyte Antigens (HLA) and aging was investigated. It is possible that HLA antigens are associated with longevity, either indirectly through disease associations or directly through involvement in the aging mechanism.

DESIGN

Community-based follow-up study.

SETTING

Leiden, the Netherlands.

PARTICIPANTS

A total of 919 subjects were HLA typed in this community-based study. All subjects were aged 85 and older and were white. Seventy-two percent of the cohort was female.

MEASUREMENTS

Age- and sex-adjusted Mortality Rate Ratios (MRR) were estimated for 79 antigens by the subject-years method. HLA-A, -B and -C typing was performed with the standard NIH lymphocytotoxicity test, HLA-DR and -DQ typing was performed with the two-color fluorescence test. Homozygosity for HLA-A, -B, and -DR was defined as only one detectable antigen at a locus.

RESULTS

The mean follow-up period (SD) was 5.0 (0.6) years. At the end of the follow-up, 70% of the subjects had died. The MRR (95% CI) for B60 was 0.96 (0.75-1.23), and for DR11 it was 0.82 (0.66-1.01). For A2 and A26 only, the MRR (95% CI) was significantly different from 1: 0.85 (0.73-0.99), P = .04 and 1.45 (1.06-1.99), P = .02, respectively (P values not corrected for the number of antigens tested). Homozygosity was not associated with mortality.

CONCLUSIONS

HLA was not associated with mortality after the age of 85. Therefore, direct involvement of HLA in aging is unlikely. We suggest that the findings of previous studies are attributable to methodological shortcomings such as small sample size and differences in genetic background of the subjects.

Genetic restriction of HIV-1 infection and progression to AIDS by a deletion allele of the CKR5 structural gene. Hemophilia Growth and Development Study, Multicenter AIDS Cohort Study, Multicenter Hemophilia Cohort Study, San Francisco City Cohort, ALIVE Study

The chemokine receptor 5 (CKR5) protein serves as a secondary receptor on CD4(+) T lymphocytes for certain strains of human immunodeficiency virus-type 1 (HIV-1). The CKR5 structural gene was mapped to human chromosome 3p21, and a 32-base pair deletion allele (CKR5Delta32) was identified that is present at a frequency of approximately0.10 in the Caucasian population of the United States. An examination of 1955 patients included among six well-characterized acquired immunodeficiency syndrome (AIDS) cohort studies revealed that 17 deletion homozygotes occurred exclusively among 612 exposed HIV-1 antibody-negative individuals (2.8 percent) and not at all in 1343 HIV-1-infected individuals. The frequency of CKR5 deletion heterozygotes was significantly elevated in groups of individuals that had survived HIV-1 infection for more than 10 years, and, in some risk groups, twice as frequent as their occurrence in rapid progressors to AIDS. Survival analysis clearly shows that disease progression is slower in CKR5 deletion heterozygotes than in individuals homozygous for the normal CKR5 gene. The CKR5Delta32 deletion may act as a recessive restriction gene against HIV-1 infection and may exert a dominant phenotype of delaying progression to AIDS among infected individuals.

The heritability of human longevity: a population-based study of 2872 Danish twin pairs born 1870-1900

The aim of this study was to explore, in a large and non-censored twin cohort, the nature (i.e., additive versus non-additive) and magnitude (i.e., heritability) of genetic influences on inter-individual differences in human longevity. The sample comprised all identified and traced non-emigrant like-sex twin pairs born in Denmark during the period 1870-1900 with a zygosity diagnosis and both members of the pairs surviving the age of 15 years. A total of 2872 pairs were included. Age at death was obtained from the Danish Central Person Register, the Danish Cause-of-Death Register and various other registers. The sample was almost non-censored on the date of the last follow-up (May 1, 1994), all but 0.6% had died, leaving a total of 2872 pairs for analysis. Proportions of variance attributable to genetic and environmental factors were assessed from variance-covariance matrices using the structural equation model approach. The most parsimonious explanation of the data was provided by a model that included genetic dominance (non-additive genetic effects caused by interaction within gene loci) and non-shared environmental factors (environmental factors that are individual-specific and not shared in a family). The heritability of longevity was estimated to be 0.26 for males and 0.23 for females. The small sex-difference was caused by a greater impact of non-shared environmental factors in the females. Heritability was found to be constant over the three 10-year birth cohorts included. Thus, longevity seems to be only moderately heritable. The nature of genetic influences on longevity is probably non-additive and environmental influences non-shared. There is no evidence for an impact of shared (family) environment.

Genetic screening, testing and treatment: how far can we go?

Treatment comes in three forms: care, control, cure; each will be part of any new development in the management of genetic disease, either Mendelian or complex. Diagnosis recognizes three states of disease: impairment, disability, and handicap when the disease is symptomatic and has manifestations. Genetics in health care has the potential to prevent these manifestations by interventions at the presymptomatic stage. Wherever cause of disease involves genotypic variation that undermines homeostasis, genetic testing and screening could play a predictive role. The area of greatest interest will be the common multifactorial diseases. While some persons worry that geneticists have taken society too fast and far along the road to ruin, it is closer to the truth that we have actually gone rather slowly and not very far along the road to better personal and collective health. With wisdom and caution the new opportunities for genetic testing or screening will become part of health care; and sooner rather than later when better treatments for our inherited infirmities are found.

Low atherosclerotic response of a strain of rabbits to diet-induced hypercholesterolemia

In this report we describe the development of two rabbit strains, HAR (high atherosclerotic response) and LAR (low atherosclerotic response), and their propensities to develop atherosclerosis in the aorta despite similar levels of diet-induced hypercholesterolemia. Sixty-two randomly selected male New Zealand White rabbits were fed a cholesterol-enriched diet (0.5%) for 84 days and developed 57 +/- 25% sudanophilic lesions of the aortic surface; 12 rabbits showed a low atherosclerotic response (0% to 30% surface involvement), and 22 rabbits showed a high atherosclerotic response (70% to 100% surface involvement). The offspring of rabbits with low atherosclerotic response were used for breeding the strain of rabbits resistant to atherosclerosis (LAR strain), while the offspring of rabbits with high atherosclerotic response were used for breeding the HAR strain. Controlled breeding was started after the 4th generation and performed for the subsequent 6 generations. Thus, in the LAR rabbits the lipid-stainable surface area of aorta amounted to only 27 +/- 17% after 112 days of cholesterol feeding. On the other hand, in HAR rabbits, aortic surface involvement reached 85 +/- 25% after 112 days on the cholesterol-enriched diet. The measurements of surface area involvement were corroborated also by a significantly lower, chemically determined cholesterol content of the aorta in LAR rabbits. Plasma lipids and lipoproteins were determined at baseline, after 21 and 42 days of cholesterol feeding, and at the time the animals were killed. The plasma cholesterol concentrations of cholesterol-fed HAR and LAR rabbits showed a 13-fold increase after 21 days and a 21-fold increase after 84 days on the cholesterol diet.(ABSTRACT TRUNCATED AT 250 WORDS)

How long can humans live? Lower bound for biological limit of human longevity calculated from Danish twin data using correlated frailty model

How long can people live? Opinions of the researchers diverge and debates continue. Is there any systematic way to address this question? In this paper, we suggest an approach to the estimation of the biological limit of human longevity using survival data for twins from different zygocity groups. The approach is based on the genetic model of individual frailty. It combines ideas used in demography and survival analysis with methods of quantitative genetics and genetic epidemiology. The association between the life-spans of related individuals is described by the correlated frailty model of bivariate survival. A version of this model is used in order to estimate heritability of the individual frailty and to calculate the lower bound of human longevity. The limitations of this approach and directions of further research are discussed.

Survival of related individuals: an extension of some fundamental results of heterogeneity analysis

"Many ideas in the analysis of heterogeneous mortality are based on the relationship between individual and observed hazard rates. This connection is established with the help of conditional averaging procedure: The observed risk of death at age x is calculated among those who survive this age. The analogy of this result for bivariate survival model with correlated individual hazards is derived. In the case of correlated frailty model the parametric specification of the mean, variance and correlation coefficient of the bivariate frailty distribution among survivors is obtained. The relationship between local association measure and the characteristics of the bivariate frailty distribution among survivors is established." (SUMMARY IN FRE)

Genetic analysis of durations: correlated frailty model applied to survival of Danish twins

Population studies of changes in human morbidity and mortality require models which take into account the influence of genetic and environmental factors on life-related durations, such as age at onset of the disease or disability, age at death, etc. In this paper we show how a bivariate survival model based on the concept of correlated individual frailty can be used for the genetic analysis of durations. Six genetic models of frailty are considered and applied to Danish twin survival data. The results of statistical analysis allow us to conclude that at least 50% of variability in individual frailty is determined by environmental factors. The approach suggests a method of estimation of the lower bound for the biological limit of human longevity. Directions for further research are discussed.

Correlated individual frailty: an advantageous approach to survival analysis of bivariate data

"We develop a new model of bivariate survival based on the notion of correlated individual frailty. We analyze the properties of this model and suggest a new approach to the analysis of bivariate data that does not require a parametric specification--but permits estimation--of the form of the hazard function for individuals. We empirically demonstrate the advantages of the model in the statistical analysis of bivariate data." (SUMMARY IN FRE)

The trauma triangle

Recent research supports the hypothesis that more active engagement of the patient in occurring illnesses improves quality of life and probably even life expectancy. In this study experience and theoretical knowledge from psychotherapy is transplanted to clinical practice in order to improve the physician's engagement in the patient-disease relationship. By defining severe and long-term illnesses as a psychotrauma, the transfer of the psychotherapeutical model leads to the creation of a new triangular relationship: patient-illness-doctor. Practical examples are used as illustrations for the conceptual differences between psychotherapy and clinical medicine. Options for dialogue show the difference between adaptation ("learning to live with") and adjustment (active coping strategies and controlling). The hypothesis is that a better dialogue will reduce illness-related stress, giving the patient better and more effective access to personal psychic and physical support systems.

Illness, the mind, and the body: cancer and immunology: an introduction

From the sixties on it has become clear how the human physical condition could be influenced by human behavior. Although hypothesis were lacking to understand these connections, nursing research especially proved how systematically introduced patient behavior during illness and hospitalization could induce better recovery results and better prognosis for the patient. Information and attitude proved to be crucial elements in these processes of improved patient expectations. It took less than two decades to get to the insights we have in 1994. Recent research shows the interlocking mechanisms of nervous and endocrine systems with the immune system as significantly being influenced by behavior and especially psychic and or psychosocial stress. This special issue of Theoretical Medicine briefly describes the historical development with contributions on the most recent state of the scientific art. These developments are emphasized by discussion on the clinical reality of the (breast) cancer patient and recent findings on the complexity of the prevalence of cancer in epidemiology. An attempt is made to consider practical consequences of the actual knowledge if applied to patient care.

Genes and family environment in familial clustering of cancer

Familial clustering of a disease is defined as the occurrence of the disease within some families in excess of what would be expected from the occurrence in the population. It has been demonstrated for several cancer types, ranging from rare cancers as the adenomatosis-coli-associated colon cancer or the Li-Fraumeni syndrome to more common cancers as breast cancer and colon cancer. Familial clustering, however, is merely an epidemiological pattern, and it does not tell whether genetic or environmental causes or both in combination are responsible for the familial clustering. Familial clustering may be due to genetic predisposition to the disease, but exposure to environmental factors--shared by members of some families, but not by members of other families--may also cause familial clustering and hence mimic genetic inheritance in the study of nuclear families. Based on assumptions regarding the individual steps in the biological process starting with exposure to carcinogens and ending with death from disseminated cancer we suggest that genetic and environmental factors may both be involved in most of these steps. The present paper focuses on research methodologies necessary to discriminate between the effect of genes and family environment in the development of cancer.

A role for molecular genetics in biological conservation

The recognition of recent accelerated depletion of species as a consequence of human industrial development has spawned a wide interest in identifying threats to endangered species. In addition to ecological and demographic perils, it has become clear that small populations that narrowly survive demographic contraction may undergo close inbreeding, genetic drift, and loss of overall genomic variation due to allelic loss or reduction to homozygosity. I review here the consequences of such genetic depletion revealed by applying molecular population genetic analysis to four endangered mammals: African cheetah, lion, Florida panther, and humpback whale. The accumulated genetic results, combined with physiological, ecological, and ethological data, provide a multifaceted perspective of the process of species diminution. An emerging role of population genetics, phylogenetics, and phylogeography as indicators of a population's natural history and its future prognosis provides valuable data of use in the development of conservation management plans for endangered species.

Genetic susceptibility to death from coronary heart disease in a study of twins

BACKGROUND

A family history of premature coronary heart disease has long been thought to be a risk factor for coronary heart disease. Using data from 26 years of follow-up of 21,004 Swedish twins born between 1886 and 1925, we investigated this issue further by assessing the risk of death from coronary heart disease in pairs of monozygotic and dizygotic twins.

METHODS

The study population consisted of 3298 monozygotic and 5964 dizygotic male twins and 4012 monozygotic and 7730 dizygotic female twins. The age at which one twin died of coronary heart disease was used as the primary independent variable to predict the risk of death from coronary heart disease in the other twin. Information about other risk factors was obtained from questionnaires administered in 1961 and 1963. Actuarial life-table analysis was used to estimate the cumulative probability of death from coronary heart disease. Relative-hazard estimates were obtained from a multivariate survival analysis.

RESULTS

Among the men, the relative hazard of death from coronary heart disease when one's twin died of coronary heart disease before the age of 55 years, as compared with the hazard when one's twin did not die before 55, was 8.1 (95 percent confidence interval, 2.7 to 24.5) for monozygotic twins and 3.8 (1.4 to 10.5) for dizygotic twins. Among the women, when one's twin died of coronary heart disease before the age of 65 years, the relative hazard was 15.0 (95 percent confidence interval, 7.1 to 31.9) for monozygotic twins and 2.6 (1.0 to 7.1) for dizygotic twins. Among both the men and the women, whether monozygotic or dizygotic twins, the magnitude of the relative hazard decreased as the age at which one's twin died of coronary heart disease increased. The ratio of the relative-hazard estimate for the monozygotic twins to the estimate for the dizygotic twins approached 1 with increasing age. These relative hazards were little influenced by other risk factors for coronary heart disease.

CONCLUSIONS

Our findings suggest that at younger ages, death from coronary heart disease is influenced by genetic factors in both women and men. The results also imply that the genetic effect decreases at older ages.

Heritability of cephalometric and occlusal variables as assessed from siblings with overt malocclusions

It has been thoroughly documented that measurements of the craniofacial complexes have moderate to high heritabilities--that they are primarily a consequence of "nature" rather than "nurture." In contrast, recent studies, which used twin and sibship analyses, have shown that malocclusions per se (i.e., measures of tooth position and dental interrelationships) have low heritabilities; malocclusions sensu stricto are primarily acquired (environmentally induced), not inherited. All such studies have, however, focused on persons not treated orthodontically. This can introduce selection bias since cases with moderate to severe malocclusions would have received treatment and, thus, be excluded from study. The present analysis addresses this issue of ascertainment bias by examining just that portion of the adolescent population receiving comprehensive orthodontics. Initial treatment records of 104 pairs of siblings were studied, all of whom subsequently received full-banded treatment. In this selected series of overt malocclusions, heritability estimates for craniometric variables were significantly lower than in a comparable series of adolescents with naturally occurring good occlusions, whereas heritability estimates for occlusal variations (e.g., rotations, crossbites, displacements) were significantly higher. This vindicates the clinical perception that siblings often present with similar malocclusions. We propose that the substantive measures of intersib similarity for occlusal traits reflect similar responses to environmental factors common to both siblings. That is, given genetically influenced facial types and growth patterns, siblings are likely to respond to environmental factors (e.g., reduced masticatory stress, chronic mouth-breathing) in similar fashions. Malocclusions appear to be acquired, but the fundamental genetic control of craniofacial form often diverts siblings into comparable physiologic responses leading to development of similar malocclusions.

Genes and environment in the inheritance of morbidity and mortality

During the past 30 years, the Danish Adoption Registry has been used in the analysis of the effect of genes and family environment on the development of mental disorders. During the last 15 years, the registry has also been used for similar analyses of somatic disorders, including obesity and premature death from somatic disorders. This article discusses the potential problems generally related to inference on morbidity from mortality data and particularly when using mortality data in adoption studies. We conclude that further insight into the question of nature, nurture or both requires extending the studies to include morbidity data as well as mortality data. We suggest that expanding the study by including biological and adoptive siblings and by using recently developed statistical methods will considerably strengthen the adoption study of morbidity and mortality.

Genetic epidemiology utilizing the adoption method: studies of obesity and of premature death in adults

Genetic epidemiology gives no priority to genes or environment in the search of disease causation. However, a major problem in this field is the disentangling of the effects of environment and genes. The study of subjects separated very early in life from their biologic parents and adopted by unrelated parents provide a strong tool for estimation of genetic and familial environmental influences. The degree to which the trait or disease frequency of the adoptees is similar to that seen among the biologic relatives is an indication of the strength of the genetic influence. Similarity to the adoptive relatives suggests influences of the family environment shared between them. Adoption studies of adult obesity show that it is genes, and not the family environment, that is responsible for the familial aggregation of obesity. A study of the mortality of adult adoptees and their biologic and adoptive parents indicates a genetic influence on the risk of premature death from all causes, from natural causes, infections, and cardio- and cerebrovascular conditions, and suggests familial environmental influences on death from the vascular causes and from cancer.

The nature/nurture controversy: spouse-likeness revisited

Within the past twelve months two distinguished scientific journals have once again raised the issue of nature versus nurture in health and sickness. The conclusion continues to be simply that both genetics and environment play a role. The issue still to be resolved is the relative contributions of nature and nurture. The model which most contributes to the answer is the very one least employed, namely spouse-likeness. This is a review of the approximately 100 most recent articles. It is evident that, within the limits of these observations, environment may play a more dominant role than generally considered.

International trends in cancer mortality in France, West Germany, Italy, Japan, England and Wales, and the USA

Age-specific worldwide trends in cancer mortality were reviewed, with emphasis on cancer sites where increases have been reported in the USA. Cancer rates vary by factors as high as 30 between all countries, and 5-fold within and between industrialised countries. In Italy, Japan, Federal Republic of Germany, England and Wales, and the USA, patterns of cancer mortality have shifted uniformly over the past two decades. Stomach cancer continues to decline, while brain and other central-nervous-system cancer, breast cancer, multiple myeloma, kidney cancer, non-Hodgkin lymphoma, and melanoma have increased in persons aged 55 and older. Cancer of the lung is starting to decline for men under age 85 and women under age 60 in England and Wales and men under age 45 in the USA, but is still rising for men and women in other countries. All forms of cancer are increasing in persons over age 54 except lung and stomach (which together comprise between 20% and 43% of all cancer in males in these countries). Studies of the quality of ascertainment and enumeration indicate that these increases are not attributable solely to diagnostic artifacts or to increased access to health care, although both these factors may be involved. These recorded increases in cancer should be assessed in greater detail to provide better projections of health care needs and to identify causal factors that may be controlled. The changes in cancer other than lung are so great and rapid that their causes demand intensive investigation.

Genetics of obesity in adult adoptees and their biological siblings

An adoption study of genetic effects on obesity in adulthood was carried out in which adoptees separated from their natural parents very early in life were compared with their biological full and half siblings reared by their natural parents. The adoptees represented four groups who by sampling from a larger population were categorised as either thin, medium weight, overweight, or obese. Weight and height were obtained for 115 full siblings of 57 adoptees and for 850 half siblings of 341 adoptees. In full siblings body mass index (kg/m2) significantly increased with weight of the adoptees. Body mass index of the half siblings showed a steady but weaker increase across the four weight groups of adoptees. There were no significant interactions with sex of the adoptees, sex of the siblings, or (for the half siblings) sex of the common parent. In contrast with the findings in half siblings and (previously) the natural parents there was a striking, significant increase in body mass index between full siblings of overweight and obese adoptees. The degree of fatness in adults living in the same environment appears to be influenced by genetic factors independent of sex, which may include polygenic as well as major gene effects on obesity.