Influence of chorionicity on the heritability estimates of blood pressure: a study in twins

BACKGROUND: A basic assumption of the twin design is that environmental influences including prenatal experiences are equal across twin types. However, the intra-uterine environment may differ according to the chorionicity of the monozygotic twins, which may have biased previous heritability estimates of blood pressure. OBJECTIVE: The aim of the present study was to assess whether the heritability of blood pressure, derived from measurements in monozygotic and dizygotic twins, differs according to the chorionicity of the monozygotic twins. METHODS: Conventional and 24-h ambulatory blood pressures were measured in 125 dizygotic twin pairs and in 97 dichorionic and 128 monochorionic monozygotic twin pairs at the age of 18-34 years. The twin sample was drawn from the East Flanders Prospective Twin Survey, in which perinatal data were collected at birth. Intra-pair correlation coefficients were calculated and compared between both types of monozygotic twin pairs. Heritability was estimated from model-fitting and path analysis, based on the dizygotic twins and, respectively, all monozygotic twins and the two subtypes. RESULTS: Intra-pair correlation coefficients for the various blood pressures, after adjustment for body mass index, ranged from 0.45 to 0.71 in the monozygotic twin pairs and did not differ significantly according to chorionicity. Heritability estimates of blood pressure were between 52 and 64%, and were similar when calculated from dizygotic twins and, respectively, dichorionic and monochorionic monozygotic twins. CONCLUSIONS: Heritability estimates of conventional and ambulatory blood pressure do not differ significantly according to the chorionicity of the monozygotic twins.     

Female monozygotic twins discordant for hemophilia A due to nonrandom X-chromosome inactivation

We describe monozygotic female twins discordant for hemophilia A, born to a carrier mother and normal father. Affected twin A presented at age 1 year with excessive bruising and factor VIII procoagulant activity (FVIII:C) of less than 1% of normal. Twin B is an asymptomatic carrier with FVIII:C level of 42%. Peripheral blood DNA was tested for X-chromosome inactivation (methylation) patterns of the X-linked human androgen receptor gene, comparing the twins' patterns to parental. Twin A showed nonrandom inactivation skewed toward the paternal X, whereas twin B showed random X-inactivation. This is the first reported case of discordance for hemophilia A between female monozygotic twins.     

Genetic effects in the response of adipose tissue lipoprotein lipase activity to prolonged exercise. A twin study

Our laboratory has reported large inter-individual differences in the metabolic response of adipose tissue to prolonged exercise in humans. The present study investigated the contribution of heredity in the metabolic changes of adipose tissue to prolonged exercise in 11 monozygotic and 10 dizygotic pairs of male twins, 18 to 27 years of age, studied immediately before and after a 90 min bout of exercise. The sum of 7 skinfold thicknesses and percent of fat from underwater weighing were used as body fat indicators (BFI). Subcutaneous adipose tissue was excised and fat cell weight (FCW) determined. The activity of adipose tissue lipoprotein lipase (LPL) released with heparin was also measured. BFI and FCW were identical in both types of twins. As previously reported, LPL activity was increased by exercise (P less than 0.01) in both type of twins. The changes observed for LPL activity were more similar in monozygotic twins than in dizygotic twins resulting in a significant level of inheritance (P less than 0.05). A genetic component for LPL activity supports the hypothesis that adipose tissue LPL could be genetically determined not only in its basal activity but also in response to stresses such as exercise.     

Heritability of polycystic ovary syndrome in a Dutch twin-family study

BACKGROUND: Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders among women of reproductive age. There is evidence for a genetic component in PCOS based on familial clustering of cases. OBJECTIVE: In the present study, the heritability of PCOS was estimated. DESIGN/PARTICIPANTS: Data from 1332 monozygotic twins (genetically identical) and 1873 dizygotic twins/singleton sisters of twins (who share on average 50% of their segregating genes) registered with The Netherlands Twin Register were used. PCOS was defined as less than nine menstrual cycles and acne or hirsutism in agreement with the 2003 Rotterdam consensus. RESULTS: Results point to a strong contribution of familial factors to PCOS. The resemblance in monozygotic twin sisters (tetrachoric correlation 0.71) for PCOS was about twice as large as in dizygotic twin and other sisters (tetrachoric correlation 0.38). Univariate analyses point to strong contributions of genetic factors to the variance in PCOS. Next, a trivariate genetic analysis of oligomenorrhea, acne, and hirsutism was carried out. This analysis confirmed that the familial component in PCOS is due to genetic factors. CONCLUSIONS: This study demonstrated a large influence of genetic factors to the pathogenesis of PCOS, justifying the search for susceptibility genes.     

Gastroesophageal reflux disease in monozygotic and dizygotic twins.

BACKGROUND & AIMS: Gastroesophageal reflux disease (GERD) interferes with the quality of life and carries an increased risk for esophageal adenocarcinoma. We investigated genetic influence in the development of reflux. METHODS: We compared concordance for reflux in monozygotic (MZ) and dizygotic (DZ) twins. All twins age 55 and older in the nationwide Swedish Twin Registry were invited to participate. Data were collected by computer-assisted telephone interviews. Reflux disease was defined by symptomatic heartburn or acid regurgitation occurring at least weekly. RESULTS: A total of 2178 monozygotic, 3219 same-sex dizygotic, and 3014 unlike-sex dizygotic twin pairs provided information. Overall, 15.3% of the twins had reflux. In men, the intraclass correlation for reflux was 0.29 (95% confidence interval [CI], 0.15-0.43) for monozygotic and 0.13 (95% CI, 0.02-0.25) for dizygotic pairs. In women, the correlation was 0.33 (95% CI, 0.22-0.44) for monozygotic and 0.14 (95% CI, 0.04-0.24) for dizygotic pairs. For unlike-sex dizygotic pairs, the correlation was 0.06 (95% CI, -0.01 to 0.14). Concordance for reflux was not caused by inherited obesity or alcohol use; inherited smoking may be a minor factor. CONCLUSIONS: The increased concordance for reflux in monozygotic pairs, compared with dizygotic pairs, indicates genetic rather than shared environmental effects. Heritability accounted for 31% (23%-39%) of the liability to reflux disease in this population.     

The influence of zygosity status on blood pressure and on lipid profiles in male and female twins

OBJECTIVE: To study the influence of zygosity on blood pressure and serum lipid concentrations among male and female twins. SETTING: Department of Endocrinology, Odense University Hospital, Denmark. PARTICIPANTS: A total of 125 monozygotic and 178 dizygotic twin pairs aged 55-74 years of age, ascertained from The Danish Twin Register. DESIGN : Population-based cross-sectional study. MAIN OUTCOME MEASURES: Blood pressure and serum lipid concentrations. RESULTs: The prevalence of hypertriglyceridemia and hypercholesterolemia were higher among monozygotic compared with dizygotic twins, whereas the prevalence of hypertension was similar. The level of triglycerides [0.28 (0.44) versus 0.18 (0.41), P = 0.01] and total cholesterol [1.82 (0.17) versus 1.78 (0.19), P = 0.03] were significantly higher in monozygotic compared with dizygotic twins. Systolic blood pressure was non-significantly higher among monozygotic twins (136.8 (21.3) versus 134.1 (19.6), P = 0.10). When comparing monozygotic and dizygotic twins within each sex group, the difference in triglyceride level was only apparent among male twins and the differences in systolic blood pressure and total cholesterol were only seen among female twins. Birth weight as determined in a subgroup of the population was similar in monozygotic and dizygotic twins. CONCLUSIONS: Zygosity status per se influences fasting serum triglycerides and total-cholesterol and to some extent systolic blood pressure in twins, supporting an influence of an intrauterine component on lipid profiles. The influence is independent of birth weight and seems to be sex-specific.     

Gender and health: a study of older unlike-sex twins

OBJECTIVES: The primary goal of this study was to assess gender differences in various measures of health conditions, symptoms, and self-rated health among older persons by comparing brothers and sisters in a sample of unlike-sex twins. METHODS: All living pairs of unlike-sex twins born between 1906 and 1925 were identified through the Swedish Twin Registry and sent surveys assessing health and other factors. This population-based sample consisted of 605 twin pairs. Paired sample t tests were used to analyze gender differences in health-related measures, including a three-level measure of health problems based on physicians' ratings. RESULTS: Women had more total health conditions, not life-threatening health conditions, somewhat life-threatening cardiovascular conditions, and physical and psychological symptoms. Men had more very life-threatening health conditions and cardiovascular conditions. No gender differences were found in somewhat life-threatening health conditions, total cardiovascular conditions, or self-rated health. DISCUSSION: Important gender differences and similarities in health were found using an unlike-sex twin design that reduced variability due to background characteristics. This design also minimized problems caused by gender differences in survival. Research on gender and health in older persons requires more detailed approaches to address the complexity of this topic.     

Acquired obesity increases CD68 and tumor necrosis factor-alpha and decreases adiponectin gene expression in adipose tissue: a study in monozygotic twins

CONTEXT: Both acquired and genetic factors regulate adipose tissue function. OBJECTIVE: We determined whether adipose tissue mRNA expression is regulated by obesity, independently of genetic effects, by studying monozygotic (MZ) twins. DESIGN: Seventeen healthy pairs of MZ twins aged 24-27 yr (body mass index 20.0-33.9 kg/m(2), intrapair differences in body weight 0.1-24.7 kg), were identified from the population-based FinnTwin16 cohort. Body fat percent was determined by dual-energy x-ray absorptiometry, sc and intraabdominal fat by magnetic resonance imaging, liver fat by proton spectroscopy, and insulin sensitivity by using the euglycemic insulin clamp technique. Adipocyte cell size and expression of 10 genes (real-time PCR) were determined in sc adipose tissue biopsies. Serum levels of some of the genes were measured using ELISA. RESULTS: Within MZ twin pairs, acquired obesity was significantly related to increased adipocyte size and increased adipose tissue mRNA expressions of leptin, TNFalpha and the macrophage marker CD68, and decreased mRNA expressions of adiponectin and peroxisome proliferator-activated receptor-gamma. Intrapair differences in liver fat correlated directly with those in leptin and CD68 expression. CD68 expression and serum TNFalpha concentrations were correlated with insulin resistance. CONCLUSIONS: Acquired obesity independent of genetic influences is able to increase expression of macrophage and inflammatory markers and decrease adiponectin expression in adipose tissue.     

Monozygotic twins with Crohn's disease and ulcerative colitis: a unique case report

Background—A large number of monozygotic anddizygotic twin pairs with inflammatory bowel disease have beenreported. To date no twin pair has developed phenotypically discordantinflammatory bowel disease. This case report is the first documentedoccurrence of discordant inflammatory bowel disease occurring inmonozygotic twins.
Case report—Twenty two year old identical maletwins presented within three months of each other with inflammatorybowel disease that proved to be discordant in overall disease type,disease distribution, clinical course, and histopathological findings. Twin 1 developed a severe pancolitis necessitating total colectomy while twin 2 developed a predominantly distal patchy colitis with frequent granulomas, controlled by aminosalicylates. Twin 1 was antineutrophil cytoplasmic antibody (ANCA) negative at the time oftesting while twin 2 (Crohn's disease) was ANCA positive.Significantly, the twins possessed the HLA type DR3-DR52-DQ2 previouslyassociated with extensive colitis.
Conclusion—This case report confirms the importantrole played by genetic factors in the development of inflammatory bowel disease. It also highlights the crucial role of undeterminedenvironmental agents in dictating disease expression and phenotype.

Keywords:monozygotic twins; ulcerative colitis; Crohn'sdisease; inflammatory bowel disease

     

Concordance for Type 2 (non-insulin-dependent) diabetes mellitus in male twins

Summary Concordance for Type 2 (non-insulin-dependent) diabetes was determined in 250 monozygotic and 264 dizygotic white male twin pairs who participated in the National Heart, Lung, and Blood Institute Twin Study. These twins were born between 1917 and 1927 and were identified from military records without regard to disease status. We examined surviving members of the cohort twice — at mean ages of 47 and 57 years — and obtained 1-h post-load glucose tests and medication histories. Diagnostic criteria for Type 2 diabetes included a glucose value13.9 mmol/l or current use of antidiabetic medication; possible Type 1 (insulin-dependent) diabetic twins were excluded. A strong genetic predisposition to Type 2 diabetes was suggested by 3 lines of evidence from the second examination: (1) 58% of monozygotic co-twins of diabetic twins were themselves diabetic compared with an expected prevalence of 10%; (2) only 1 of 15 originally disease-discordant, monozygotic twin pairs remained discordant for diabetes; and (3) 65% of non-diabetic monozygotic co-twins of diabetic twins had elevated glucose values. Because concordance for diabetes was less than 100% for twins aged 52–65 years and because twins varied in age at onset of disease, non-genetic factors may also influence diabetes development. Among the 19 monozygotic twins pairs discordant for diabetes, diabetic twins did not differ from their non-diabetic co-twins in obesity, diet, alcohol consumption, or education. However, compared with unrelated nondiabetic twins of the same ages, non-diabetic co-twins of diabetic twins gained more weight as adults (p<0.02) and had higher glucose levels (p<0.03).     

Individual differences in locus of control during the second half of the life span for identical and fraternal twins reared apart and reared together

The relative influences of genetic and environmental factors for components of locus of control (LOC) were examined in the Swedish Adoption/Twin Study of Aging. The sample consisted of 84 pairs of monozygotic twins separated at an early age and reared apart, 173 pairs of dizygotic twins reared apart, 129 monozygotic pairs reared together, and 168 dizygotic pairs reared together. At the time of data collection, 72% were over 50 years of age. Three LOC components were measured in a mailed questionnaire: sense of personal control or lack of control over the direction of one's own life (Life Direction), beliefs about how responsible people are for misfortunes in their lives (Responsibility), and beliefs concerning the role of luck in determining people's outcomes (Luck). Model-fitting results indicated that genetic influences were of importance for Life Direction and Responsibility, accounting for somewhat over 30% of the variance in each component, while environmental influences explained twin similarity for Luck.     

No association between birth weight and Type 1 diabetes mellitus--a twin-control study.

AIMS: To investigate, by means of a twin-control study, whether there is a relationship between birth weight and Type 1 diabetes mellitus. METHODS: In the youngest part (n = 20 888 pairs) of the Danish Twin Register, 95 twin pairs (26 monozygotic and 69 dizygotic) with Type 1 diabetes were identified. Information about birth weight and birth length, prematurity, maternal age and parity was obtained from midwives' records and from the Danish Medical Birth Registry and analysed using Student's two-sided t-test, Chi-square test and logistic regression. RESULTS: Birth data were available for 83 diabetic and 51 healthy twin individuals, altogether 67 twin pairs (20 monozygotic and 47 dizygotic). Mean birth weight was 2537 g and 2565 g (NS) in monozygotic and dizygotic pairs and the corresponding length at birth 47.6 cm and 48.2 cm (NS). In pairs discordant for diabetes, the mean birth weight was 2538 g in twins with diabetes and 2549 g in twins without diabetes (NS). Logistic regression in discordant pairs showed no relationship between diabetes status and birth weight, birth length, birth order, sex or prematurity. Logistic regression in concordant vs. discordant pairs showed no effect of mean birth weight and birth length, maternal age, parity or weeks of prematurity. CONCLUSIONS: There is no association between Type 1 diabetes mellitus and birth weight in this study. Furthermore, variables related to birth weight and length cannot explain why some pairs are concordant while other remain discordant.     

Leptin, insulin, insulin-like growth factors and their binding proteins in cord serum: insight into fetal growth and discordancy

OBJECTIVE: Singleton infants with intrauterine growth restriction have an adaptive hormonal profile characterized by decreased levels of IGF-1, IGF-2, IGFBP-3 and insulin and elevated levels of IGFBP-1 and IGFBP-2. This study examined the association between cord serum levels of six growth factors and anthropometric features at birth in twins in order to determine the intrauterine growth factor interactions and to characterize the specific hormonal profile of small discordant twins. DESIGN: Prevalent case-control study. PATIENTS: Twenty pairs of discordant twins (5 monozygotic, 15 dizygotic) and 20 pairs of concordant twins (6 monozygotic, 14 dizygotic) matched for gestational age. MEASUREMENTS: Cord blood levels of IGF-1, IGF-2, IGFBP-1, IGFBP-3, insulin, leptin and anthropometric measurements at birth. Intra- and inter-pair differences and correlation coefficients were calculated, and the data were fitted to multivariate regression models. RESULTS: In both discordant and concordant groups, the smaller twins had a significantly lower level of IGF-1 (P < 0.03) and significantly higher level of IGFBP-1 (P < 0.02) than their larger cotwins. IGFBP-1 was inversely correlated with IGF-1 (P < 0.05). Insulin levels were significantly higher in the smaller discordant than the smaller concordant twins (P < 0.001) and in the larger discordant than the larger concordant twins (P < 0.004). Among the monozygotic twins, the leptin level was significantly higher in the larger discordant than the larger concordant twins (P < 0.025). Percentage birth weight discordancy was statistically correlated with twin-pair differences in IGF-1 and IGFBP-1. CONCLUSIONS: Of the six factors studied, IGF-1 appears to be the main indicator of intrauterine growth. Twin discordancy may involve compensatory rather than adaptive mechanisms or a multihormone relative resistance syndrome.     

Economic evaluation of screening for familiar form of arrhythmogenic right ventricular cardiomyopathy in Poland

BACKGROUND: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a myocardial disease associated with fibrofatty tissue replacement in heart muscle leading to arrhythmia, heart failure or sudden death (SCD) often being the first manifestation in probands. At least 50% of cases of ARVC are inherited. AIM: To evaluate costs and cost-effectiveness of diagnosis of the disease in asymptomatic relatives in Poland. METHODS: 239 asymptomatic subjects (mean age 35 years, 120 male) belonging to 42 families affected with ARVC were examined between May 2003 and May 2005. The costs of outpatient visits and additional diagnostic tests were included. Payer perspective was used. RESULTS: In all individuals ECG and transthoracic echocardiography were performed. Magnetic resonance imaging and signal-averaged ECG were performed in 35 patients suspected of having ARVC. The diagnostic criteria for ARVC were fulfilled in 29 patients and 57 subjects were recognised borderline. Total costs of screening amounted to 71 090 PLN (approximately 20,000 euro). The average cost per one case of detected ARVC was 2451 PLN (approximately 680 euro). CONCLUSIONS: Costs of early detection of ARVC in individuals with a family history of the disease in Polish settings are low. Due the avilability of primary prevention of SCD the family screening in asymptomatic subjects is a cost-effective procedure.     

Adaptive changes to training in adipose tissue lipolysis are genotype dependent

In order to study the effects of heredity and of physical training on adipose tissue morphology and metabolism, 15 pairs of monozygotic twins (MZ) (six males and nine females), aged from 16 to 24 years, weighing 56.2 +/- 9.1 kg and with 13.9 +/- 8.2 percent body fat, were submitted to a biopsy of adipose tissue in the suprailiac region. In addition, eight pairs of twins (four male and four female) took part in a 20-week ergocycle training program, five days a week, 40 min a day, at 80 percent of their maximal heart rate. Adipocyte diameter (AD) was assessed on collagenase isolated fat cells. Basal (BL), epinephrine submaximal (10(-5) M) (ESML) and epinephrine maximal stimulated lipolysis (10(-4) M) (EML) were determined on isolated fat cells. Intraclass correlation coefficients indicated significant intrapair resemblance before training for all fat morphological and metabolic indicators (0.78 less than or equal to ri less than or equal to 0.93). Training significantly increased VO2 max (pre: 44.7 +/- 7.6 (ml/kg) vs post: 50.8 +/- 5.0; P less than or equal to 0.001). No training effect was found in percent body fat and AD. Training significantly increased BL, ESML, and EML (P less than or equal to 0.01). Moreover, twins of the same MZ pair yielded identical responses in ESML and EML with training. Intraclass coefficients for the magnitude of change in activity over pretraining values reached 0.84 and 0.90 respectively. Apparently a genetically determined response to training could not be found for BL. These results show that training per se has an effect on adipose tissue lipolysis beyond variation in fatness. Furthermore, sensitivity of stimulated lipolysis to training appears to have a genetic basis.     

Carvedilol therapy improved left ventricular function in a patient with arrhythmogenic right ventricular cardiomyopathy

An asymptomatic 35 year-old man was referred to our hospital because of abnormal ECG findings. The ECG showed complete right bundle branch block and left anterior hemiblock. Echocardiography revealed a moderately enlarged right ventricle (RV) and an apical aneurysm. RV wall motion showed diffusely moderate impairment, while the systolic function of the left ventricle (LV) was slightly decreased. The ejection fractions (EF) of the RV and LV were calculated as 28.1% and 41.9% by Simpson's method using multiple cardiac computed tomography (CT) scans. A 24 hour ambulatory ECG showed only 372 single premature ventricular contractions (PVC). Cardiac catheterizaion revealed that the RV was enlarged with prominent trabeculation and decreased motion. In an electrophysiologic study, neither electrical stimulation of the RV nor electrical stimulation plus isoproterenol infusion could induce ventricular tachycardia. Pathological examination of a biopsy from the interventricular septum of the RV revealed fibrofatty change in the myocardium. Based on these results, we made a diagnosis of arrhythmogenic right ventriclular cardiomyopathy (ARVC) and administered 5 mg of carvedilol. Sixty days after the initiation of carvedilol therapy, we performed repeat cardiac CT. The EF of the LV was markedly improved from 41.9% to 62.0%, although the EF of the RV was not changed. The number of PVCs showed no change. This case suggests that carvedilol is not only useful for controlling arrhythmia but also for improving left ventriclular function in some patients with ARVC. Sympathetic overactivity is reported to cause sudden death, so carvedilol may be a first-line drug for some patients with ARVC.     

Heritability of left ventricular mass in a large cohort of twins

INTRODUCTION: Left ventricular hypertrophy is recognized as one of the most important independent predictors of adverse cardiovascular outcome. The aetiology of LVH includes a number of well-recognized causes but there is considerable interest in the genetics of cardiac muscle hypertrophy. We used a large prospective twin database in order to establish the heritability of left ventricular mass (LVM). METHODS: Normotensive twins were prospectively recruited. Demographic data were collected. The LVM was determined using the Penn formulae derived from data collected from echocardiography. RESULTS: A total of 376 Caucasian twin pairs (182 monozygotic and 194 dizygotic) aged 25-79 years were recruited. All subjects were normotensive with no significant differences in blood pressure (mean blood pressure: monozygotic twins, 132/83 mmHg; dizygotic twins, 131/82 mmHg) or body mass index between the monozygotic and dizygotic twins. The mean LVM for monozygotic twins was 140.9 g, compared with 140.2 g for dizygotic twins. Heritability estimates suggest that the genetic variance of LVM is 0.59 (95% confidence interval, 0.5-0.67). No common shared environmental effects were identified under this model. CONCLUSION: Our data from the largest set of twin pairs studied to date show that LVM has a sizeable genetic basis that is probably polygenic. This result has important implications for the understanding of normal and abnormal cardiac morphology at the molecular level.     

CARD15/NOD2 polymorphisms do not explain concordance of Crohn''s disease in Swedish monozygotic twins

BACKGROUND: CARD15/NOD2 polymorphisms are associated with Crohn's disease. There is a high concordance for disease and disease phenotype in monozygotic twin pairs with Crohn's disease. AIM: We studied CARD15/NOD2 polymorphisms in a Swedish, population-based cohort of monozygotic twins with Crohn's disease to assess whether these variants explain disease concordance. SUBJECTS AND METHODS: Twenty-nine monozygotic twin pairs (concordant n=9, discordant n=20) with Crohn's disease and 192 healthy controls were investigated for the CARD15/NOD2 variants Arg702Trp, Gly908Arg and Leu1007fsinsC. RESULTS: CARD15/NOD2 mutations were found in 5/38 (13%) twins with Crohn's disease, corresponding to a total allele frequency of 6.6%. Only 2/9 concordant twin pairs carried any of the variants and the remaining seven were wild type genotype. The total allele frequency was 4.4 times higher (95% confidence interval 1.0-21.5, p=0.06) in concordant twins than in discordant ones, 11.1% versus 2.5%. In healthy controls the total allele frequency was 2.6%. CONCLUSIONS: CARD15/NOD2 polymorphisms contribute but do not alone explain concordance of Crohn's disease in monozygotic twins and, at least in a Swedish population, other polymorphisms are required. The low occurrence of CARD15/NOD2 mutations in the study and other Northern European populations suggests that these variants are of less importance in Northern Europe.     

Inflammatory bowel disease in a Swedish twin cohort: a long-term follow-up of concordance and clinical characteristics

BACKGROUND & AIMS: In 1988, we reported the first twin study in inflammatory bowel disease. The aim of the current study was to follow up these twins regarding new cases of inflammatory bowel disease and Crohn's disease characteristics using the Vienna classification. METHODS: The official Swedish population register and the cause of death register were used to search for the twins. All living patients were interviewed. RESULTS: Three monozygotic twins earlier classified as healthy had been diagnosed with inflammatory bowel disease (ulcerative colitis, n = 2; Crohn's disease, n = 1). Retrospectively, all 3 were symptomatic at the original survey. This changed the pair concordance in monozygotic twins from 6.3% to 18.8% in ulcerative colitis and from 44.4% to 50.0% in Crohn's disease. A high degree of concordance regarding age at diagnosis, disease location at diagnosis and during the course, and disease behavior was found in concordant monozygotic twin pairs with Crohn's disease. Seven of 9 pairs were identical in 3 or more of these disease characteristics compared with an expected number of 1.5 (P = 0.000076). CONCLUSIONS: This study confirms that the genetic influence is stronger in Crohn's disease than in ulcerative colitis. A remarkable phenotype similarity within concordant pairs with Crohn's disease was found using the Vienna classification.     

Occurrence of rheumatoid arthritis in a nationwide series of twins

The nationwide Finnish Twin Cohort was linked with the Sickness Insurance Register on the basis of the unique identification number assigned to each Finnish citizen. The study series consisted of 4137 monozygotic (MZ) and 9162 dizygotic (DZ) same-sexed twin pairs born before 1958 and alive in 1975. Altogether, 261 subjects in the series had the right to receive free medication for rheumatoid arthritis (RA) under the Sickness Insurance Act that covers the entire Finnish population. The pairwise concordance percentage for RA was 12.3 in MZ twins and 3.5 in DZ twins. The age and sex adjusted ratio of observed per expected numbers of concordant pairs (relative risk) was 8.6 for MZ pairs and 3.4 for DZ pairs. These figures are lower than those previously reported on twins but compatible with results from family studies on the genetic component of RA.