Exclusion of linkage of Crohn's disease to previously reported regions on chromosomes 12, 7, and 3 in the Belgian population indicates genetic heterogeneity

Susceptibility to inflammatory bowel disease (IBD) is significantly determined by genetic factors. Linkage data from genome-wide searches have identified regions on chromosomes 16, 12, 7, and 3. Our goal was to replicate these four regions in a Belgian population of IBD families. Fifty-four IBD families were studied (47 with Crohn's disease [CD] and 7 with mixed CD and ulcerative colitis, containing 79 affected sibpairs (68 CD only, 11 mixed) for the regions previously implicated to chromosomes 16, 12, 7, and 3. In this study, no evidence for linkage was found on any of the four chromosomal regions studied for either the whole IBD dataset or the CD subgroup. The multipoint maximum logarithm of odds scores were less than 0.7 for all four regions. Exclusion mapping could significantly exclude chromosomes 3, 7, and 12. Despite earlier findings, we could significantly exclude linkage of CD with previously reported regions on chromosomes 12, 7, and 3, and could not find evidence for linkage to chromosome 16. It is important to report these findings in light of the genetic heterogeneity of IBD. A genome-wide search on a larger group of affected siblings is being analyzed to detect other possible susceptibility loci in the Belgian population.

A quantitative study of unpaid caregiving in multiple sclerosis

Data on healthcare utilisation by MS patients of different grades of disability were collected using the method of a prospective diary. Professional care providers and unpaid caregivers noted during 4 weeks the time they spent and the types of support they provided. The total homecaring time of family and friends amounted to 4.6 and 12 h per day for the moderately and the severely disabled MS patients respectively. The time for unpaid core activities such as mobility help, nursing care and personal care of moderately and severely disabled patients amounted to 0.5 and 2 h per day, exceeding the time for professional medical and paramedical care at home. Eighty per cent of informal homecaring is provided by persons living with the patients, primarily the partner, who provides 60% of homecaring time. Severely disturbed bowel function and absence of a partner were associated with permanent institutionalisation. Multiple Sclerosis (2000) 6 274 - 279

Predictive power of individual genetic and environmental factor scores

This study explores the use of an individual's genetic (IGFS) and environmental factor score (IEFS), constructed using genetic model fitting of a multivariate strength phenotype. Maximal isometric and dynamic strength measures, one maximal repetition load (1RM) and muscle cross-sectional area (MCSA) were measured in 25 monozygotic and 16 dizygotic twin pairs. The use of IGFS and IEFS in predicting the sensitivity to environmental stress was evaluated by the association of the scores with strength training gains after a 10-week high resistance strength training programme. Results show a high contribution of genetic factors to the covariation between maximal strength and muscle cross-sectional area (84-97%) at pre-training evaluation. Individual factor scores explained the largest part of the variation in IRM and other strength measures at pre-training and post-training evaluation respectively. Genes that are switched on due to training stress (gene-environment interaction) could explain the decrease in explained variation over time. A negative correlation was found between IGFS and strength training gains (-0.24 to -0.51, P < 0.05); individuals with a high IGFS tend to gain less strength than individuals with low IGFS. Individual environmental factor scores have lower differential power. The predictive value of the IGFS has potential utility in identifying an individual's susceptibility to environmental stress in a variety of multifactorial characteristics, eg diseases and impairments, and for selection of sib pairs for QTL analyses.

Genetic variance of adolescent growth in stature

The aim of this study is to quantify the genetic and environmental variation in biological parameters of the adolescent growth in stature in both sexes, using structural equation models. Standing height was measured in 99 twin pairs from the Leuven Longitudinal Twin Study. Subjects were seen at semi-annual intervals between 10 and 16 years and at 18 years. Preece-Baines model I was fitted to the individual data and biologically meaningful parameters were derived. Path models were fitted to these parameters and a gender heterogeneity analysis was performed. A model including additive genetic and specific environmental factors (AE-model), allowing for a difference in total variance or in genetic/environmental variance components in males and females best explains most of the growth characteristics. For the timing and velocity of the adolescent growth spurt, no gender heterogeneity was observed, and the genetic (0.89 to 0.93) and specific environmental (0.07 to 0.11) contributions were equal in both sexes. For stature at take-off, stature at peak height velocity and for adult stature, gender heterogeneity was observed and different models appeared to result in the best fit for boys and girls. For height at PHV and adult stature, the significant contribution of a common environmental (0.39 to 0.56) factor in boys was noteworthy. For percentage of adult stature and distances between relevant time points of the growth curve, a non-scalar effect was observed, indicating that different genes affect these characteristics in boys and girls. It is concluded that most characteristics of the growth spurt in stature are under strong genetic control. Gender heterogeneity is present for stature and for a number of derived growth characteristics.

[Role of inheritability of tooth form, tooth malformation and tooth position]

A common technique to divide the influence of heredity and environment on certain characteristics, or pathologies is the one that uses twins. There are more or less complex techniques to carry out twin research, from which the most simple procedure consists of determining the amount of concordance of certain characteristics in monozygotic (MZ) and dizygotic (DZ) twins. In individuals who develop from one oocyte, like MZ twins, one would expect a correlation of 1.00 (or 100% concordance) purely from their gene-relation. DZ twins are the result of separate conceptions of the same parents and they thus differ as much from each other as ordinary brothers and sisters. The most recently developed twin-methodologies use path analysis and model fitting for the estimations of the heritabilities and environmental influences on certain characteristics. In this article it is tried to picture the genetic an environmental influence on tooth form, tooth position and occlusal characteristics with different genetic techniques. Generally it can be concluded that our genes are of utmost importance for tooth form and tooth malformations, but the environment has a much bigger impact on tooth position and occlusal parameters.

The contribution of genes, environment and of body mass to blood pressure variance in young adult males

OBJECTIVE

(1) To determine by means of multivariate genetic modelling whether the covariation of blood pressure (BP) and body mass index (BMI) is compatible with a direct effect of BMI on BP, or rather with pleiotropy or environmental association, and (2) to quantify the contribution of such an effect and of heritability and environmental factors to BP variance.

DESIGN AND METHODS

Fifty monozygous and 41 dizygous male twin pairs (ages: 17-38 years) were studied. BMI was calculated as weight/height. Blood pressure was the mean of three conventional measurements in the supine position. Estimates for the path coefficients of the three hypothesised models were obtained using Maximum Likelihood Estimation and were used to calculate the predicted covariance matrices for these models. A chi2 goodness-of-fit index of P>0.05 indicated an adequate fit. Likelihood ratio chi2 statistics and the Akaike Information Criterion (AIC) were used to choose the best model among the fitting models. The path coefficients of the best model were used to estimate the variance decomposition of BP.

RESULTS

All hypothesised models fitted the data. The AIC was lowest for the model representing an influence of BMI on BP, for both systolic (AIC = -22.3) and diastolic (AIC = -22.2) BP. The estimated percentages of the total phenotypic variance of BP, which could be explained by the influence of BMI on BP, were 11.4% and 12.9% for systolic and diastolic pressure respectively. The remaining variances were associated with variation in genetic and environmental factors.

CONCLUSIONS

A direct influence of BMI on BP constitutes the most likely explanation of the BP-BMI-covariation and it accounts for about 12% of the BP-variance in young healthy men.

M235T angiotensinogen gene polymorphism and cardiovascular renal risk

OBJECTIVE

In this meta-analysis, we attempted to derive pooled estimates for the putative associations between various cardiovascular-renal disorders and the M235T polymorphism of the angiotensinogen gene.

METHODS

Case-control studies were combined, using the Mantel and Haenszel approach. Joint P values for continuous variables were calculated by Stouffer's method. Continuous measurements reported in different units were expressed on a percentage scale using the intrastudy mean of the MM genotype as denominator.

RESULTS

The computerized database used for this analysis included 69 reports with an overall sample size of 27,906 subjects. Overall, possession of the T allele was associated with an increased risk of hypertension. In comparison with the MM reference group (number of studies, n = 32), the excess risk was 31% (P = 0.001) in TT homozygotes and 11% (P = 0.03) in TM heterozygotes. The sensitivity analysis showed that this association was present only in whites (T allelic frequency, f = 42.2%), but not in blacks (f = 77.0%) or Asians (f = 78.0%). Atherosclerotic complications (n = 12), renal microvascular disorders (n = 13), cardiomyopathy (n = 2) or diabetic retinopathy (n = 3) were not correlated with the M235T polymorphism. Publication bias was observed for hypertension, but not for coronary heart disease, including myocardial infarction, and for microvascular nephropathy. Furthermore, in comparison with the MM control group, the circulating angiotensinogen levels (n = 8) were raised by 11 and 7% (P = 0.01) in TT and TM subjects, respectively. In contrast, plasma levels of the angiotensin I converting enzyme (n = 4) and body mass index (n = 15) were not associated with the T allele.

CONCLUSION

The T allele encoding angiotensinogen is not associated with atherosclerotic or microvascular complications, but in Caucasians behaves as a marker for hypertension. This association, which may have been inflated by publication bias, does not necessarily imply causality.

The East Flanders Prospective Twin Survey (Belgium): a population-based register

The East Flanders Prospective Twin Survey (EFPTS), started in 1964, is unique among the 17 major European twin registers because it is population based, the twins (and higher order births) are ascertained at birth, basic perinatal data are collected, chorion type is established and, when appropriate, genetic markers including DNA fingerprints, are determined. The total number of sets is 5089 twin, 158 triplet and 14 of higher order. Zygosity has been diagnosed on the basis of sex, placental structure and genetic markers in more than 95% of pairs. The EFPTS is the only large register that includes placental data and allows differentiation of three subtypes of monozygotic twins based on the time of the initial zygotic division: the dichorionic-diamnionic pairs (early), the monochorionic-diamnionic pairs (intermediate), and the monochorionic-monoamnionic pairs (late). Methodology and basic results in twins are considered in this article; detailed studies will be reported later. The sex proportion in dizygotic (DZ) twins is the same as in singletons, whereas monozygotic (MZ) twins number more girls than boys. The difference in perinatal mortality between DZ and MZ twins is limited to the monochorionic MZ subgroup. Birth weight is highest in DZ twins and diminishes stepwise in MZ dichorionic and MZ monochorionic twins. Duration of pregnancy follows the same trend but is limited to a few days. Iatrogenic pregnancies are increasing to the point of representing almost 50% of the twin births in 1997.

A genetic study of anteroposterior and vertical facial proportions using model-fitting

Genetic model-fitting was used to determine the heritability of anteroposterior and vertical facial proportions in twins. Lateral headplates of 33 monozygotic and 46 dizygotic twins, none of whom had undergone orthodontic treatment, were used. Five proportions, based on four vertical and five horizontal measurements, were assessed: lower facial height, anterior- to posterior-facial height, total facial height to face depth, sella-A-point to sella-B-point, and sella-upper incisal edge to sella-lower incisal edge. Reproducibility was high for all variables. Model-fitting indicated that all the facial proportions were controlled by additive genes and the specific environment. The genetic component was 71% for upper-to lower-facial height, 66% for anterior- to posterior-facial height, 62% for total facial height, and 66% for sella-A-point to sella-B-point and sella-upper incisal edge to sella-lower incisal edge.

Commitment to X inactivation precedes the twinning event in monochorionic MZ twins

To gain insight into the timing of twinning, we have examined a closely related event, X-chromosome inactivation, in female MZ twin pairs. X-inactivation patterns in peripheral blood and buccal mucosa were compared between monochorionic MZ (MC-MZ) and dichorionic MZ (DC-MZ) twins. Overall, the MC-MZ twins displayed highly similar X-inactivation patterns, whereas DC-MZ twins frequently differed in their X-inactivation patterns, when both tissues were tested. Previous experimental data suggest that commitment to X inactivation occurs when there are 10-20 cells in the embryo. Simulation of embryo splitting after commitment to X inactivation suggests that MC-MZ twinning occurs three or four rounds of replication after X inactivation, whereas a DC-MZ twinning event occurs earlier, before or around the time of X inactivation. Finally, the overall degree of skewing in the MZ twins was not significantly different from that observed in singletons. This indicates that X inactivation does not play a direct role in the twinning process, and it further suggests that extreme unequal splitting is not a common mechanism of twin formation.

Univariate and multivariate genetic analysis of subcutaneous fatness and fat distribution in early adolescence

Univariate and multivariate analyses of the genetic and environmental contributions to variance in adipose tissue and adipose tissue distribution were carried out in early adolescents. Stature, weight, body mass index (BMI), and five subcutaneous skinfolds were measured at half-yearly intervals in 105 MZ and DZ twin pairs from 10 to 14 years. The most parsimonious model, which provided an adequate explanation for variation in the BMI, five skinfolds, and the T/E ratio, included additive genetic and specific environmental factors. Multivariate analyses of the genetic architecture of subcutaneous fat indicated a general skinfold genetic factor, an extremity skinfold genetic factor, and skinfold specific genetic factors. This implies that all skinfolds are under control of the same set of genes, that a different set of genes partly controls extremity skinfolds, and that other genes have a small skinfold specific impact. Environmental contributions included a general skinfold environmental factor and skinfold specific environmental factors. BMI is under control of the same set of genes as skinfolds and shows high genetic correlations with trunk skinfolds, which implies that nearly the same genes may influence trunk skinfolds and the BMI. All models were fairly consistent across the age range.

Strength training: importance of genetic factors

PURPOSE

This study focuses on the quantification of genetic and environmental factors in arm strength after high-resistance strength training.

METHODS

Male monozygotic (MZ, N = 25) and dizygotic (DZ, N = 16) twins (22.4 +/- 3.7 yr) participated in a 10-wk resistance training program for the elbow flexors. The evidence for genotype*training interaction, or association of interindividual differences in training effects with the genotype, was tested by a two-way ANOVA in the MZ twins and using a bivariate model-fitting approach on pre- and post-training phenotypes in MZ and DZ twins. One repetition maximum (1RM), isometric strength, and concentric and eccentric moments in 110 degree arm flexion at velocities of 30 degrees x s(-1), 60 degrees x s(-1), and 12 degrees x s(-1) were evaluated as well as arm muscle cross-sectional area (MCSA).

RESULTS

Results indicated significant positive training effects for all measures except for maximal eccentric moments. Evidence for genotype*training interaction was found for 1RM and isometric strength, with MZ intra-pair correlations of 0.46 and 0.30, respectively. Bivariate model-fitting indicated that about 20% of the variation in post-training 1RM, isometric strength, and concentric moment at 120 degrees x s(-1) was explained by training-specific genetic factors that were independent from genetic factors that explained variation in the pretraining phenotype (30-77%).

CONCLUSIONS

Genetic correlations between measures of pre- and post-training strength were indicative for high pleiotropic gene action and minor activation of training-specific genes during training.

Inheritance of static and dynamic arm strength and some of its determinants

Maximal static, eccentric and concentric torques and arm components estimated by anthropometry and measured by computed tomography were evaluated in 25 male monozygotic twins and 16 dizygotic twins (22.4 +/- 3.7 years). The importance of genetic and environmental factors in the observed variation in these measurements was estimated by genetic model-fitting techniques. In this sample of young adult male twins, genetic factors were significant in most of the strength measurements, arm muscle components and muscle activation variables. The contribution of genetic factors in strength measures depended on the angle, contraction type and to some extent on contraction velocity. For isometric strength, angle-specificity in genetic and environmental variation could be attributed to the degree of variability in muscle activation and performance discomfort at each specific angle, with the highest unique environmental impact at extreme angles. The high genetic contribution at 170 degrees, but not at 50 degrees, possibly expressed different contributions of genetic factors in the muscle-length factor and moment arm in torques at both angles. The importance of genetic factors in eccentric arm flexor strength (62-82%) was larger than for concentric flexion (29-65%), as the pattern of genetic determination followed the torque-velocity curve. Genetic variations in contractile and elastic components, contributing differently to eccentric and concentric torques, together with velocity-dependent actin-myosin binding factors, could account for the observed differences. The broad heritability was very high for all anthropometric and arm cross-sectional area measurements (> 85%) and common environmental factors were only significant for anthropometrically estimated mid-arm muscle tissue are (48%). Heritability estimates of different arm muscularity measurements were comparable.

Validation of a telephone zygosity questionnaire in twins of known zygosity

The aim of this study was to validate a zygosity questionnaire that can be administered over the telephone. Mothers of same-sexed twins of known zygosity and chronicity between 2 and 31 years of age were interviewed on a nine-item questionnaire. From the answers one unweighted and four weighted indices were computed. As single questions, the mother's opinion and the "two peas in a pod" question differentiated best between monozygotic and dizygotic twins. One independent well-trained observer assessed the zygosity based on the questionnaire and made the correct diagnosis in 96% of the cases. A weighted index of eight similarity questions yielded an accuracy of 98%. This study shows that the zygosity of same-sexed twins more than 2 years old and without gross physical malformation can reliably be determined by a telephone questionnaire with a high accuracy.

Utilisation and cost of professional care and assistance according to disability of patients with multiple sclerosis in Flanders (Belgium)

OBJECTIVES

To assess the utilisation of medical services and social (community) assistance in patients with multiple sclerosis of different disability and to calculate the direct healthcare costs to society.

METHODS

(1) One hundred and eighty four patients with multiple sclerosis were classified into four grades of disability according to a simplified Kurzke disability status scale. (2) Patients were interviewed with a structured questionnaire containing questions on their sociodemographic status, the use of inpatient and outpatient medical services and pharmaceutical products during the previous year, the use of social assistance, and the purchase of prosthetics and charges for house adaptations during the previous five years. (3) Data were also prospectively collected by means of four week diary annotations of all medical and social acts and their duration.

RESULTS

After correction for the disability distribution the yearly costs for the 5500 patients with multiple sclerosis in Flanders was estimated to be ECU 13106000 for ambulatory care including rehabilitation and district nursing and ECU 3234000 for pharmaceutical products. To these direct medical costs ECU 3491000 for social assistance and ECU 4938000 for prosthetics and adaptations should be added. The yearly costs for admissions to hospital including permanent residence in an institution and pharmacy was ECU 26581000 . Home nursing and long term or permanent residence in an institution of the most severely disabled, 17% of the multiple sclerosis population, are responsible for 50% of the total direct healthcare costs and care for the 6.5% institutionalised patients accounts for 23%. Direct costs for medical care and social assistance for patients with multiple sclerosis, who account for about 0.1 % of the total population, amounts to 1% of the total healthcare budget in Flanders.

CONCLUSION

This information on utilisation of medical services and social assistance can be used for good healthcare planning and cost effectiveness studies.

Anticipation in familial Crohn's disease

BACKGROUND

Offspring with a family history of Crohn's disease have an earlier age of onset than their parents. This might be due to genetic anticipation, characterised by earlier and/or more severe disease in subsequent generations.

AIMS

To investigate the possibility of genetic anticipation in affected parent-child pairs with Crohn's disease from France and Belgium.

PATIENTS AND METHODS

In a cohort of 160 multiply affected families with Crohn's disease, 57 parent-first affected child pairs were detected. Clinical characteristics (age at diagnosis, disease extent, and type) of both parents and children were registered and compared.

RESULTS

Children were younger than their parents at diagnosis in 48/57 (84%) pairs. The median age at diagnosis was 16 years younger in children than in parents (p < 0.0001). However, the difference was related to the age at diagnosis in the parents and was not present in 12 parent-child pairs with an early age at diagnosis for the parents. In most cases, disease extent and type were not considered more severe in children than in parents. Parental sex affected neither age at diagnosis nor extent and type of disease in children.

CONCLUSION

Patients in the second affected generation acquire their disease at an earlier time in life in some but not all familial cases of Crohn's disease. Several explanations including genetic anticipation and environmental factors might explain this phenomenon.

Treatment of acute ischemic stroke with piracetam. Members of the Piracetam in Acute Stroke Study (PASS) Group

BACKGROUND AND PURPOSE

Piracetam, a nootropic agent with neuroprotective properties, has been reported in pilot studies to increase compromised regional cerebral blood flow in patients with acute stroke and, given soon after onset, to improve clinical outcome. We performed a multicenter, randomized, double-blind trial to test whether piracetam conferred benefit when given within 12 hours of the onset of acute ischemic stroke to a large group of patients.

METHODS

Patients received placebo or 12 g piracetam as an initial intravenous bolus, 12 g daily for 4 weeks and 4.8 g daily for 8 weeks. The primary end point was neurologic outcome after 4 weeks as assessed by the Orgogozo scale. Functional status at 12 weeks as measured by the Barthel Index was the major secondary outcome. CT scan was performed within 24 hours of the onset of stroke but not necessarily before treatment. Analyses based on the intention to treat were performed in all randomized patients (n = 927) and in an "early treatment" population specified in the protocol as treatment within 6 hours of the onset of stroke but subsequently redefined as less than 7 hours after onset (n = 452).

RESULTS

In the total population, outcome was similar with both treatments (the mean Orgogozo scale after 4 weeks: piracetam 57.7, placebo 57.6; the mean Barthel Index after 12 weeks: piracetam 55.8, placebo 53.1). Mortality at 12 weeks was 23.9% (111/464) in the piracetam group and 19.2% (89/463) in the placebo group (relative risk 1.24, 95% confidence interval, 0.97 to 1.59; P = .15). Deaths were fewer in the piracetam group in those patients in the intention-to-treat population admitted with primary hemorrhagic stroke. Post hoc analyses in the early treatment subgroup showed differences favoring piracetam relative to placebo in mean Orgogozo scale scores after 4 weeks (piracetam 60.4, placebo 54.9; P = .07) and Barthel Index scores at 12 weeks (piracetam 58.6, placebo 49.4; P = .02). Additional analyses within this subgroup, confined to 360 patients with moderate and severe stroke (initial Orgogozo scale score < 55), showed significant improvement on piracetam in both outcomes (P < .02).

CONCLUSIONS

Piracetam did not influence outcome when given within 12 hours of the onset of acute ischemic stroke. Post hoc analyses suggest that piracetam may confer benefit when given within 7 hours of onset, particularly in patients with stroke of moderate and severe degree. A randomized, placebo-controlled, multicenter study, the Piracetam Acute Stroke Study II (PASS II) will soon begin.

The deletion/insertion polymorphism of the angiotensin converting enzyme gene and cardiovascular-renal risk

OBJECTIVE

This meta-analysis attempted to derive pooled estimates for the associations between various cardiovascular-renal disorders and the deletion/insertion (D/I) polymorphism of the angiotensin converting enzyme (ACE) gene.

METHODS

Case-control studies were combined, using the Mantel-Haenszel approach. Joint P values for continuous variables were calculated by Stouffer's method. Continuous measurements reported in different units were expressed on a percentage scale using the within-study mean of the II genotype as the denominator.

RESULTS

The computerized database used for this analysis included 145 reports with an overall sample size of 49 959 subjects. Overall, possession of the D allele was associated with an increased risk of atherosclerotic and renal microvascular complications. In comparison with the II reference group, the excess risk in DD homozygotes (P < 0.001) was 32% for coronary heart disease (CHD; 30 studies), 45% for myocardial infarction (20 studies), 94% for stroke (five studies) and 56% for diabetic nephropathy (11 studies). The corresponding risk in DI heterozygotes amounted to 11% (P= 0.02), 13% (P= 0.02), 22% (P= 0.10) and 40% (P < 0.001), respectively. Hypertension (23 studies), left ventricular hypertrophy (five studies), hypertrophic or dilated cardiomyopathy (eight studies) and diabetic retinopathy (two studies) were not related to the DI polymorphism. Publication bias was observed for CHD, myocardial infarction and microvascular nephropathy, but not hypertension. In studies with DNA amplification in the presence of insertion-specific primers, the risk associated with the DD genotype increased to 150% [95% confidence interval (CI) 76-256; four studies] for diabetic nephropathy, but decreased to 12% (95% CI -3 to 28; seven studies) for CHD and 14% (95% CI -6 to 37; four studies) for myocardial infarction. On the other hand, the pooled odds ratios did not materially change if the meta-analysis was limited to articles published in journals with an impact factor of at least 4. Furthermore, compared with the II control group, the circulating ACE levels (29 studies) were raised 58 and 31% (P < 0.001) in DD and DI subjects, respectively. In contrast, plasma renin (10 studies), systolic and diastolic blood pressure (46 studies) and body mass index (30 studies) were not associated with the D allele.

CONCLUSION

The D allele is not associated with hypertension, but behaves as a marker of atherosclerotic cardiovascular complications and diabetic nephropathy. These associations do not necessarily imply a causal relationship and may have been inflated by publication bias. Nevertheless, their possible therapeutic implications may be subject to further investigation in prospective (intervention) studies.

Genetic variability in the renin-angiotensin system: prevalence of alleles and genotypes

BACKGROUND

Variants of the human genes coding for renin, angiotensin-converting enzyme (ACE), angiotensinogen (AGT) and the angiotensin II type-I receptor (AT1R) are inconsistently associated with cardiovascular-renal disease, possibly because of genetic differences in the background populations.

METHODS

This systematic review of the literature investigated genetic variation in the renin system according to race, sex and age. Across studies with relevant information, multivariate analyses also accounted for the methods of genotyping and the enrollment of subjects as controls, cases or groups studied cross-sectionally.

RESULTS

The 185 reviewed reports included 64978 subjects. In five studies (n=989) on the renin gene, the Hind III and Taq I polymorphisms varied with the groups' average age, whereas the Bg I, Bg II and Hind III but not Taq I sites differed according to race. Among 135 studies (n=44697) on the deletion/insertion (D/I) polymorphism of the ACE gene, the frequency of the D allele was 54.0%. Its prevalence was not related to sex and black race, was 49.9% lower in Asians, 10.0% lower in studies relying on I-specific primers, 4.9% higher for each 25-year increment in the average age of the groups studied, and 16.7% higher in cases than controls. Among 12 studies (n=4952) on the T174-->M variant of the AGT gene, the M174 frequency was 11.0%, did not vary according to sex and enrollment group, was 56.7% lower in blacks and 39.5% lower for each 25-year increase in the groups' mean age. Across 44 studies (n=16713) on the M235-->T substitution in the AGT gene, the T235 prevalence was 51.6%. Its frequency was not related to sex and the method of genotyping, tended to be 7.5% lower for each 25-year increase in average age, was from 4.6 to 6.6 times higher in nonwhites than whites and 13.2% higher in cases than controls. Among 13 studies (n=4332) on the A1166-->C variant of the AT1R gene, the C1166 allelic frequency was 25.7%. Its prevalence was independent of the enrollment group, 77.4% lower in Asians, and nearly doubled for each 25-year increment in age.

CONCLUSION

With adjustments applied for the subjects' enrollment group and the methods of genotyping, genetic polymorphism in the renin system varies according to race and age, but not sex. One possible application of the present results is to provide allelic and genotypic frequencies, which could be used to assess power, to perform sample size calculations, or to predict selection bias in future studies.

Clustering of increased small intestinal permeability in families with Crohn's disease

BACKGROUND & AIMS

Small intestinal permeability is increased in a proportion of patients with Crohn's disease (CD) and a subset of their healthy relatives. A primary permeability defect was postulated in the pathogenesis of the disease. The aim of this study was to identify a possible genetic pattern in the distribution of CD and/or abnormal permeability.

METHODS

Differential urinary excretion of lactulose and mannitol (L/ M) in complete CD families was determined. Controls included healthy families and families with ulcerative colitis. Pedigrees were used to compare the distribution of CD and/or increased permeability.

RESULTS

The L/M was significantly increased in patients with CD. Seventeen of 67 first-degree relatives (25%) had a ratio greater than the upper limit (P95 = 0.0170). Permeability results of CD families showed a highly significant familial aggregation. The lack of a genetic pattern in relation with CD and occurrence of disturbed permeability especially within generation, points toward a shared environmental factor. Five of 14 healthy spouses (36%) of patients with CD had also an increased permeability, and prevalence of increased permeability was not higher in families with known familial occurrence (P = 0.85).

CONCLUSIONS

This large family study confirms an increased permeability in a subset of healthy relatives of patients with CD. However, the absence of a typical family pattern and the high prevalence in spouses is in favor of a common nongenetic factor or a subclinical disease manifestation.

The genetic contribution to dental maturation

It has been established in the literature that there is a major genetic impact on tooth size (Potter et al., 1976; Corruccini and Sharma, 1985; Sharma et al., 1985), tooth morphology (Kraus and Furr, 1952; Biggerstaff, 1970), and root formation (Garn et al., 1960; Green and Aszkler, 1970). None of the studies concerning root formation, however, used the more advanced method of path analysis and model fitting to estimate genetic influence. The aim of the present study was to determine the genetic and environmental influence on dental maturation. Dental age scores were determined on panoramic radiographs of 58 pairs of twins--26 monozygotic (MZ) and 32 dizygotic (DZ)--with the method of Demirjian et al. (1973). No mirror-image effect was found between the sides of the same individual or between twin members, so dental maturation seems to be symmetrical for both left and right sides of the mandible. Correlation coefficients were significantly higher in MZ than in DZ twins, which suggests a genetic influence. Model fitting showed that the variation in dental age was best explained by additive genetic influences (A-component) (43%) and by environmental factors common to both twins (C-component) (50%). The specific environment (E-component) added only 8% to the model. The importance of the common environmental factor can be explained by the fact that twins, being raised together, share the same prenatal, natal, and immediate post-natal conditions that are of importance for the formation of the teeth.