La sideremia nei gemelli (Studio su 23 coppie MZ e 24 coppie DZ)

The Authors have studied the blood iron level in 94 twins (23 MZ and 24 DZ pairs) aged from 6 to 14 years.

Through the determination of the blood iron level a mean value of 45,59 mgs per 100 cc. of blood has been established. This value corresponds to that of single-born children of the same age; thus, the anemia ferri priva observed by Woodruff in twins during the first year of age may not apply to ensuing ages.

The comparison of the blood iron level at the ages taken into consideration has shown a slights progressive lowering of the blood iron, which the Authors consider physiological. The comparison of the blood iron level between MZ and DZ twin-pairs has not revealed a significantly different behavior. The twin test appears thus to demonstrate that the blood iron level is not genotypically determined, but is environment-conditioned, generally through thermic and gaseous exchanges between the organism and the environment in which it lives.

Heritability of Longitudinal Measures of Body Mass Index and Lipid and Lipoprotein Levels in Aging Twins

Body-mass index (BMI), total cholesterol (TC), lowdensity lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG) levels are known to be highly heritable. We evaluated the genetic and environmental relationships of these measures over time in an analysis of twin pairs. Monozygotic (235 pairs) and dizygotic (260 pairs) male twins were participants in the National Heart Lung and Blood Institute Veteran Twin Study, and were followed with three clinical exams from mean age 48 years to mean age 63 years. Structural equation modeling (SEM) with adjustment forAPOEgenotype (a significant contributor to TC and LDL-C) was used to assess longitudinal patterns of heritability. Results indicated a contribution of genetic factors to BMI, TC, LDL-C, HLD-C, and TG. Modest increases over time were observed in the heritability of BMI (from 0.48 to 0.61), TC (from 0.46 to 0.57), LDL-C (from 0.49 to 0.64), and HDL-C (from 0.50 to 0.62), but this trend was not present for TG. There was a corresponding decrease in shared environmental influences over time for these traits, although shared environment was a significant contributor only for HDL-C. Moreover, we observed that genetic influences for all measures were significantly correlated over time, and we found no evidence of age-specific genetic effects. In summary, longitudinal analyses of twin data indicate that genetic factors do not account for a significant proportion of the variation in age-related changes of BMI or lipid and lipoprotein levels.

A Longitudinal Genetic Study of Plasma Lipids in Adolescent Twins

Plasma lipids such as high-density lipoprotein (HDL), low-density lipoprotein (LDL), total cholesterol and triglyceride levels contribute to variation in the risk of cardiovascular disease. The early stages of atherosclerosis in childhood have also been associated with changes in triglycerides, LDL and HDL. Heritability estimates for lipids and lipoproteins for adolescents are in the range .71 to .82, but little is known about changes of genetic and environmental influences over time in adolescence. We have investigated the contribution of genetic and environmental influences to variation in lipids in adolescent twins and their nontwin siblings using longitudinal twin and family data. Plasma HDL and LDL cholesterol, total cholesterol and triglycerides data from 965 twin pairs at 12, 14 and 16 years of age and their siblings have been analyzed. Longitudinal genetic models that included effects of age, sex and their interaction were fitted to assess whether the same or different genes influence each trait at different ages. Results suggested that more than one genetic factor influences HDL, LDL, total cholesterol and triglycerides over time at ages 12, 14 and 16 years. There was no evidence of shared environmental effects except for HDL and little evidence of long-term nonshared environmental effects was found. Our study suggested that there are developmental changes in the genes affecting plasma lipid concentrations across adolescence.

Heritabilities of Alcohol Use Disorders Identification Test (AUDIT) scores and alcohol biomarkers in Koreans: the KoGES (Korean Genome Epi Study) and Healthy Twin Study

BACKGROUND

Both the Alcohol Use Disorders Identification Test (AUDIT) and alcohol biomarkers are used to screen for alcohol problems. The purpose of this study was to examine the genetic and environmental contributions to the AUDIT score and alcohol biomarkers in Koreans.

METHODS

The study included 1678 current alcohol drinkers: 818 Korean twins and 860 their families. The Korean version of AUDIT and alcohol biomarkers, i.e., gamma glutamyltransferase (GGT), alanine aminotransferase (ALT), mean corpuscular volume (MCV), and triglycerides (TG), were studied. The analyses were conducted using variance components method to estimate heritability and common environmental effects, and bivariate analyses for genetic and environmental correlations between the AUDIT score and the biomarkers after adjustment for age, gender, interaction of age and gender, smoking status, the amount of consumed alcohol, body mass index, and education.

RESULTS

Heritabilities for the AUDIT score were 0.35 and 0.40-0.71 for biomarkers (P<0.001). The risk of alcohol problems using AUDIT score was positively associated with the levels of biomarkers (GGT, MCV, and TG) in men, while the relationship was significant only for MCV in women. Genetic or environmental correlations between the AUDIT score and some of the biomarkers (GGT and MCV) were significant in men, but not significant in women.

CONCLUSIONS

We found a significant genetic contribution to the AUDIT score and the alcohol biomarkers. As there were significant genetic and environmental relationships between the AUDIT score and the alcohol biomarkers in men, future studies are warranted to identify common genes and environmental effects affecting the relationships.

Genetic effects on toxic and essential elements in humans: arsenic, cadmium, copper, lead, mercury, selenium, and zinc in erythrocytes

BACKGROUND AND OBJECTIVES

An excess of toxic trace elements or a deficiency of essential ones has been implicated in many common diseases or public health problems, but little is known about causes of variation between people living within similar environments. We estimated effects of personal and socioeconomic characteristics on concentrations of arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), selenium (Se), and zinc (Zn) in erythrocytes and tested for genetic effects using data from twin pairs.

METHODS

We used blood samples from 2,926 adult twins living in Australia (1,925 women and 1,001 men; 30-92 years of age) and determined element concentrations in erythrocytes by inductively coupled plasma-mass spectrometry. We assessed associations between element concentrations and personal and socioeconomic characteristics, as well as the sources of genetic and environmental variation and covariation in element concentrations. We evaluated the chromosomal locations of genes affecting these characteristics by linkage analysis in 501 dizygotic twin pairs.

RESULTS

Concentrations of Cu, Se, and Zn, and of As and Hg showed substantial correlations, concentrations of As and Hg due mainly to common genetic effects. Genetic linkage analysis showed significant linkage for Pb [chromosome 3, near SLC4A7 (solute carrier family 4, sodium bicarbonate cotransporter, member 7)] and suggestive linkage for Cd (chromosomes 2, 18, 20, and X), Hg (chromosome 5), Se (chromosomes 4 and 8), and Zn {chromosome 2, near SLC11A1 [solute carrier family 11 (proton-coupled divalent metal ion transporters)]}.

CONCLUSIONS

Although environmental exposure is a precondition for accumulation of toxic elements, individual characteristics and genetic factors are also important. Identification of the contributory genetic polymorphisms will improve our understanding of trace and toxic element uptake and distribution mechanisms.

Heritability and environmental factors affecting vitamin D status in rural Chinese adolescent twins

CONTEXT

Factors associated with the high prevalence of vitamin D deficiency in China are not well described, especially among Chinese adolescents.

OBJECTIVES

The aim of the study was to examine important environmental or sociodemographic factors influencing 25-hydroxyvitamin D [25(OH)D] levels and estimate its heritability.

DESIGN

A sample of 226 male and female adolescent twins aged 13-20 yr from a large prospective twin cohort of rural Chinese children and adolescents that has been followed for 6 yr were evaluated.

MAIN OUTCOME MEASURE(S)

Blood level of 25(OH)D was measured using tandem mass spectrometry methodology.

RESULTS

The overall mean (SD) 25(OH)D level was 18.0 (9.4) ng/ml, with wide variation by gender and season. In males (47.4% of subjects), the mean (SD) 25(OH)D level was 12.1 (4.2) ng/ml in non-summer and 27.4 (8.8) ng/ml in summer; in females, it was 10.1 (4.1) ng/ml in non-summer and 19.5 (6.3) ng/ml in summer. A multivariate model that included gender, age, season, physical activity, and student status demonstrated that male gender, summer season, and high physical activity significantly increased 25(OH)D levels. Summer season and male gender also significantly decreased the risk of being in the lowest 25(OH)D tertile. Overall, 68.9% of the variability in 25(OH)D level was attributable to additive genetic influence. Stratification by gender found that in males, 85.9% of the variability in 25(OH)D level was attributable to such influence, but in females, it was only 17%.

CONCLUSION

In this sample of rural Chinese adolescents, 25(OH)D level was influenced by gender, season, and physical activity level. There was a strong genetic influence on 25(OH)D level in males only.

The effect of genetic variation in the type 1 deiodinase gene on the interindividual variation in serum thyroid hormone levels: an investigation in healthy Danish twins

INTRODUCTION

Genetic factors have a considerable influence on serum thyroid hormone levels. The C785T and A1814G polymorphisms, located in the 3' untranslated region of the type 1 deiodinase (D1) gene have been associated with serum FT4 and rT3 levels.

OBJECTIVE

In healthy Danish twins, we examined the association of these polymorphisms with serum thyroid hormone levels and determined the proportion of genetic influence explained by these variants. We analysed the underlying functional mechanism by performing mRNA stability measurements and analysed the effect of these variants on D1 activity.

METHODS

Serum thyroid measurements and genotypes of the D1-C785T and D1-A1814G polymorphisms were determined in 1192 twins. Structural equation modelling was used to determine heritability estimates. Functional analyses were carried out in D1-transfected JEG3 cells.

RESULTS

Carriers of the D1-785T allele had 3.8% higher FT4 and 14.3% higher rT3 levels, resulting in a lower T3/T4 and T3/rT3 ratio and a higher rT3/T4 ratio. This polymorphism explained 0.87% and 1.79%, respectively, of the variation in serum FT4 and rT3. The D1-A1814G polymorphism was not associated with serum thyroid hormone levels. No differences in D1 mRNA decay rate or D1 activity were observed between wild-type D1 and the two variants.

CONCLUSION

The D1-C785T polymorphism is consistently and significantly associated with serum thyroid hormone levels. However, the proportion of genetic influence explained by this particular polymorphism is small. No effect of the polymorphism on D1 mRNA decay rate or D1 activity was observed. The underlying functional mechanism needs to be elucidated.

[Study on the activity of serum bone alkaline phosphatase and its relations to the heritability among pre-puberty twins]

OBJECTIVE

To evaluate calcium deficiency and demand in pre-puberty twins and to analyze the heritability of serum bone alkaline phosphatase (BALP).

METHODS

A total of 73 pairs of twins aged 9-16 years were examined by BALP test. Microsatellite polymorphism was used to diagnose the zygosity of twins, while both intraclass correlation coefficient method and Christian formula were performed to investigate heritability of serum BALP.

RESULTS

The results of zygosity diagnosis displayed that 34 pairs of twins were monozygotic (MZ) twins and 39 pairs were dizygotic (DZ) twins. 97.9% of the subjects appeared unusual in the activity of BALP, with activity of BALP > 250 U/L in 43.1% of subjects and 200-250 U/L in 54.8% of the subjects. The intake of calcium was unsatisfied in 48.4% of the boys and 39.0% in girls. Less than 10.0% of the subjects were satisfied with the intake of calcium in each age group while over 45.0% of the subjects in 10-13 age group were deficient in calcium. Differences between the means of BALP in different sex groups (t = 1.633, P = 0.105) and different age groups (F = 0.323, P = 0.924) were not statistically significant. Heritability analysis displayed that intra-class variation, inter-class variation, intra-class correlation coefficient were 191.54, 1462.22, 0.77 in MZ twins, and those were 491.03, 1475.57, 0.50 in DZ twins respectively with the heritability of BALP activity as 0.54.

CONCLUSION

Calcium deficiency is commonplace in pre-puberty twins. Our data showed that the BALP activity was influenced both by genetic (54%) and environmental (46%) factors.

Cerebral white matter in early puberty is associated with luteinizing hormone concentrations

Puberty is a period in which cerebral white matter grows considerably, whereas gray matter decreases. The first endocrinological marker of puberty in both boys and girls is an increased secretion of luteinizing hormone (LH). Here we investigated the phenotypic association between LH, global and focal gray and white matter in 104 healthy nine-year-old monozygotic and dizygotic twins. Volumetric MRI and voxel-based morphometry were applied to measure global gray and white matter and to estimate relative concentrations of regional cerebral gray and white matter, respectively. A possible common genetic origin of this association (genetic correlation) was examined. Results showed that higher LH levels are associated with a larger global white matter proportion and with higher regional white matter density. Areas of increased white matter density included the cingulum, middle temporal gyrus and splenium of the corpus callosum. No association between LH and global gray matter proportion or regional gray matter density was found. Our data indicate that a common genetic factor underlies the association between LH level and regional white matter density. We suggest that the increase of white matter growth during puberty reported earlier might be directly or indirectly mediated by LH production. In addition, genes involved in LH production may be promising candidate genes in neuropsychiatric illnesses with an onset in early adolescence.

Evidence of genetic effects on blood lead concentration

BACKGROUND

Lead is an environmental pollutant that causes acute and chronic toxicity. Surveys have related mean blood lead concentrations to exogenous sources, including industrial activity, use of lead-based paints, or traffic density. However, there has been little investigation of individual differences in lead absorption, distribution, or toxicity, or of genetic causes of such variation.

OBJECTIVES

We assessed the genetic contribution to variation in blood lead concentration in adults and conducted a preliminary search for genes producing such variation.

METHODS

Erythrocyte lead concentration was measured by inductively coupled plasma mass spectrometry in venous blood samples from 2,926 Australian adult male and female twins. Mean lead concentrations were compared by place of residence, social class and education, and by the subjects' age, sex, alcohol intake, smoking habits, iron status, and HFE genotype.

RESULTS

After adjustment for these covariates, there was strong evidence of genetic effects but not for shared environmental effects persisting into adult life. Linkage analysis showed suggestive evidence (logarithm of odds = 2.63, genome-wide p = 0.170) for a quantitative trait locus affecting blood lead values on chromosome 3 with the linkage peak close to SLC4A7, a gene whose product affects lead transport.

CONCLUSIONS

We conclude that genetic variation plays a significant role in determining lead absorption, lead distribution within the body, or both.

[Analysis on the association between two polymorphism haplotypes of lipoprotein lipase gene and serum lipids in twins of China]

OBJECTIVE

To investigate the association between haplotypes of S447X and Hind III polymorphisms of lipoprotein lipase (LPL) gene and serum lipids in a population-based twin cohort study in China.

METHODS

Twin subjects were collected based on the twin registry system of China. All twins were investigated by a standard questionnaire and physical examinations. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was used to detect the genotypes of S447X and Hind III polymorphisms. Linkage disequilibrium test and haplotypes were estimated between two polymorphisms.

RESULTS

Nine hundred and eighty-seven pairs of twins were eligible for analysis. The two polymorphisms of LPL gene were significantly linkage disequilibrium. In female twins, the H- allele of Hind III polymorphism was significantly related to lower levels of triglycerides(TG) and lower risk of high TG dislipidemia, but those associations disappeared after adjusting the polymorphism of S447X. The H- X haplotype of those two polymorphisms was significantly related to lower TG and TG/HDL (decreasing 12.9% and 14.9% respectively), as well as significantly to lower risk of high TG dislipidemia (OR = 0.40).

CONCLUSION

The haplotypes of S447X and Hind III polymorphisms were significantly related to the favorable effect of lipids,but this effect was mostly determined by the polymorphism of S447X, while the effect of Hind III polymorphism was indirectly influenced by the linkage disequilibrium with S447X polymorphism.

Serum total testosterone levels in a patient with late onset 21-hydroxylase deficiency and a twin gestation

OBJECTIVE

To present serum androgen levels during pregnancy in a twin gestation complicated by maternal late onset 21-hydroxylase deficiency.

DESIGN

Case report.

SETTING

University teaching hospital reproductive endocrinology and infertility practice.

PATIENT(S)

A 27-year-old with nonclassic 21-hydroxylase deficiency and infertility, twin female fetuses, and elevated androgens.

INTERVENTION(S)

Steroid replacement.

MAIN OUTCOME MEASURE(S)

Serum T and 17-hydroxyprogesterone (17-OHP) levels.

RESULT(S)

Elevated androgen levels persisted throughout pregnancy in spite of aggressive steroid replacement. However, twin girls were born without any evidence of virilization.

CONCLUSION(S)

The changes associated with a twin gestation may result in excessive stimulation of androgens in mothers with nonclassic 21-hydroxylase deficiency. However, the increased placental aromatase provides protection.

Relationship between twin-to-twin delivery interval and umbilical artery acid-base status in the second twin

The purpose of this study was to determine the effect of twin-to-twin delivery interval on umbilical artery acid-base status of the second twin at birth. This was a retrospective cohort study of all live-born twins with measured acid-base status in umbilical arterial blood who were delivered after 34 weeks' gestation from June 2003 to February 2006. Twins with any maternal or fetal complications were excluded. Subjects were divided into two groups based on the mode of delivery of the first twin: normal cephalic vaginal deliveries (n=40) or cesarean deliveries (n=67). The inter-twin differences in umbilical arterial blood pH, PCO(2), PO(2), and base excess in twin newborns born vaginally were significantly greater than the corresponding differences in those born by cesarean section. A significant positive correlation was found between twin-to-twin delivery interval and inter-twin difference in umbilical arterial blood pH in twin newborns born vaginally. The umbilical arterial blood pH of the second twin was less than 7.0 in 14% (2/14) in cases delivered more than 20 min after the first twin. The umbilical arterial blood gas status of the second twin worsened with increasing twin-to-twin delivery interval, and pathologic fetal acidemia (pH<7.0) might develop in the second twin when the twin-to-twin delivery interval was greater than 20 min.

The influence of birth weight and genetic factors on lipid levels: a study in adult twins

Twins can be used to investigate the biological basis for observed associations between birth weight and later disease risk, as they experiencein uterogrowth restriction compared with singletons, which can differ in magnitude within twin pairs despite partial or total genetic identity. In the present study, sixty monozygotic and seventy-one dizygotic same-sex twin pairs aged 19–50 years and eighty-nine singleton controls matched for age, gestational age, sex, maternal age and parity were recruited from an obstetric database. Associations between fasting lipid levels and birth weight were assessed by linear regression with adjustment for possible confounding factors. Twins were significantly lighter at birth but were not significantly different in adult height, weight or lipid levels from the singleton controls. There was a significant inverse association between birth weight and both total and LDL-cholesterol levels among singleton controls (−0·53mmol/l per kg (95% CI −0·97, −0·09),P=0·02 and −0·39mmol/l per kg (95% CI −0·76, −0·02),P=0·04, respectively), but there was no significant association between birth weight and lipid levels in either unpaired or within-pair analysis of twins. The results suggest that thein uterogrowth restriction and early catch-up growth experienced by twins does not increase the risk of an atherogenic lipid profile in adult life.

[Change of dehydroepiandrosterone in serum of 6 - 18 year-old twin girls in Qingdao City]

OBJECTIVE

To explore the change of serum dehydroepiandrosterone (DHEAS) concentrations throughout the puberty of girls and estimate the effects of genetic and environmental factors on serum DHEAS.

METHODS

The study population consists of 360 girls aged 6 to 18 years:132 pairs monozygotic twins and 48 pairs dizygotic twins, who were all from Qingdao city, Shan-dong province. Anthropometric measurement and pubertal development stage were determined by Tanner standard, fasting serum DHEAS contents were assayed by RIA.

RESULTS

Serum DHEAS concentrations increased from Tanner I to IV and decreased later, heritability of pubertal girl's serum DHEAS was 0.65. The heritability of 3 different pubertal stages (pre-thelarche, post-thelarche and pre-menarche, and post-menarche) were 0.92, 0.73 and 0.67 respectively.

CONCLUSION

Serum DHEAS concentrations of pubertal girls could be mainly influenced by the genetic factors, especially in the period of adrenarche. Therefore, genetic influence might be important in adrenarche-related metabolic disorders.

Mutagen sensitivity has high heritability: evidence from a twin study

Despite numerous studies showing that mutagen sensitivity is a cancer predisposition factor, the heritability of mutagen sensitivity has not been clearly established. In this report, we used a classic twin study design to examine the role of genetic and environmental factors on the mutagen sensitivity phenotype. Mutagen sensitivity was measured in peripheral blood lymphocytes from 460 individuals [148 pairs of monozygotic (MZ) twins, 57 pairs of dizygotic (DZ) twins, and 50 siblings]. The intraclass correlation coefficients were all significantly higher in MZ twins than in dizygotes (DZ pairs and MZ-sibling pairs combined) for sensitivity to four different mutagen challenges. Applying biometric genetic modeling, we calculated a genetic heritability of 40.7%, 48.0%, 62.5%, and 58.8% for bleomycin, benzo[a]pyrene diol epoxide, gamma-radiation, and 4-nitroquinoline-1-oxide sensitivity, respectively. This study provides the strongest and most direct evidence that mutagen sensitivity is highly heritable, thereby validating the use of mutagen sensitivity as a cancer susceptibility factor.

Evidence of age-dependent genetic influences on plasma total cholesterol

BACKGROUND

Causes of variation in cardiovascular risk factors include biological variation within individuals, and more permanent differences between individuals, which are at least partly genetic in origin. We have compared the magnitude of genetic and non-genetic factors within and across occasions through repeated measures of plasma cholesterol in twin subjects, and have also determined how far the same genes affect cholesterol levels at different ages.

METHODS

Data on plasma total cholesterol were extracted for 208 twin pairs who had provided blood on up to six occasions across a period of 17 years. They were aged 18-30 years at the time of first study and 30-47 at the time of the last. Multivariate models of variation due to genetic, shared environmental and unique environmental factors were fitted to the multi-occasion data and the proportions of variation due to these factors were estimated.

RESULTS

One genetic factor influenced plasma cholesterol on all occasions and a second genetic factor only influenced cholesterol results on the fifth and sixth occasions 10-17 years after the first. Environmental factors did not have significant long-term effects.

CONCLUSIONS

We conclude that individuals' long-term mean plasma cholesterol values are strongly genetically determined, but that some of these genes are age-specific in their effects.

Levetiracetam Pharmacokinetics in Neonates at Birth

Based on blood sampling in a formula-fed pair of twins, the estimated serum half-life of levetiracetam (LEV) at birth is 16-18 h.

Elevated IGFBP-1 cause high bone turnover in growth-restricted monochorionic twins with discordant birth weight

OBJECTIVE

To test the hypothesis that low birth weight twins have a higher risk of osteoportotic fracture in later life, we investigated the association between fetal IGF axis and type-1 collagen markers of bone turnover in monochorionic (MC) twins with or without discordant birth weight of >or=20%.

METHODS

Maternal and cord bloods were collected from gestational age matched MC twins of discordant (n = 16) and concordant birth weights (n = 16). The samples were assayed for cross linked carboxyl terminal telopeptide (ICTP, a marker of bone resorption) and pro-peptide (PICP, a marker of bone formation) of type I collagen, IGF-1, and IGFBP-1 by radio-immunoassay.

RESULTS

The growth-restricted twins (IUGR) of discordant group had higher fetal IGFBP-1 and ICTP (P < 0.001) levels, while PICP (P < 0.001) was lower than the co-twins with normal weight (AGA). In contrast, cord blood levels of IGF-1, IGFBP-1, ICTP, and PICP in concordant twin pairs were comparable to AGA twins. The concordant and AGA twins had a positive correlation between ICTP and PICP levels (y = 23x - 711; r = 0.84; P < 0.001; n = 48) but no such association was found in IUGR twins. Instead, IGFBP-1 levels in IUGR twins had a negative association with PICP (r = 0.81; P < 0.001; n = 16) and a positive correlation with ICTP (r- = 0.51; P < 0.05; n = 16). No such association was found in concordant and AGA twins.

CONCLUSION

These data suggest that growth-restricted twins had high bone turnover, due to elevated IGFBP-1. This association seems to be independent of maternal and genetic factors.

Genetic dissection of gene expression observed in whole blood samples of elderly Danish twins

The microarray technique is an important tool in gene expression analysis to study the activities of thousands of genes measured by their transcript levels under disease or laboratory controlled experimental conditions. Recent studies have suggested a genetic component in the variations of gene expression thus indicating the important role of genetic control over gene activities. In this study, we analyze and report the twin correlation on gene expression in whole blood samples of six female Danish twin pairs aged from 81 to 85 years. We studied the expression phenotype by treating the measured gene expression as a quantitative trait and introducing analytical approaches including the traditional twin methods in population genetics and the multivariate statistical methods. Using this combinatory approach, we were able to estimate and compare the twin correlation on the expression phenotype while accounting for systematic influence in microarray experiments. Analyses on our twin data detected a significant correlation on the expression levels of the actively regulated genes in both monozygotic and dizygotic twins, which is more pronounced in monozygotic twins. Gene ontology analysis has shown that these actively regulated genes are predominantly involved in defense and immune responses against antigenic stimulus. In conclusion, the correlation patterns revealed in our twin data provide evidence of the existence of a heritable mechanism in gene expression regulation persistently functioning even in aged subjects.

Genetic analysis of indicators of cholesterol synthesis and absorption: lathosterol and phytosterols in Dutch twins and their parents

Significant familial aggregation was observed for plasma levels of lathosterol (an indicator of whole-body cholesterol synthesis) and plant sterols campesterol and beta-sitosterol (indicators of cholesterol absorption) in 160 Dutch families consisting of adolescent mono- and dizygotic twin pairs and their parents. For lathosterol a moderate genetic heritability in parents and offspring (29%) was found. In addition, shared environment also contributed significantly (37%) to variation in plasma lathosterol concentrations in twin siblings. However, a model with different genetic heritabilities in the two generations (10% in parents and 68% in offspring) fitted the data almost as well. For plasma plant sterol concentrations high heritabilities were found. For campesterol heritability was 80% and for beta-sitosterol it was 73%, without evidence for differences in heritability between sexes or generations. No influence of common environmental influences shared by family members was seen for either campesterol or beta-sitosterol. Taken together, these results confirm and expand the hypothesis that individual differences in plasma levels of noncholesterol sterols are moderately (lathosterol) to highly (plant sterols) heritable.

[Haemolytic disease of the newborn--from a mother with anti-Kell, anti-E and anti-Vel anti-erythrocyte alloantibodies]

A grave form of HDN (haemolytic disease of the new-born) is described in female twins, caused by Kell, E and Vel isoimmunisation. The weakly vital and anaemic new-born babies were hospitalised with signs of respiratory distress on the first day of their life after the delivery by Caesarean section in the 38 (th) week of pregnancy in the General Hospital Dubrovnik. Already during the first hours of their life jaundice developed with a high bilirubin level for their age. The direct Coombs' test on the twins and the indirect Coombs' test on the mother were positive. Immuno-haematological analysis proved the presence of anti-Kell, anti-E and the very rare anti-Vel antibodies in the mother's serum and in the plasma of both twins. We had no possibility to obtain appropriate blood for the indicated exsanguine transfusion because cross-probes with the accessible blood samples were positive. Up to the fourteenth day of life the anaemia deepened and was aggravated in one twin, the Kell positive one (phenotype CcDEe,Kk) in relation to the other, the Kell negative (phenotype CcDEe,kk) twin. The recovery of the female twins started on the 15 (th) day of life, after the transfusion of blood (phenotype: 0,ccddee, Vel negative, Kel negative), received from the bank of rare blood groups in London. This is the first described case of haemolytic disease of the new-born caused by antibodies on the antigen Kell, E and Vel. The low frequency of immunisation with rare antigens such as Kell, E and Vel, does not exclude the possibility of the occurrence of grave forms of haemolytic disease. All pregnant women with a positive indirect Coombs' test should be further immuno-haematologically tested in order to identify the antibodies type so that the treatment of the new-borns could be commenced in time.

Genetics of Dizygotic Twinning: A Feasibility Study for a Biobank

To locate the genes that make a substantial contribution to variation in natural dizygotic twinning in humans, large-scale studies are needed. New studies should not stop at DNA genotyping, but collect material that allow gene-expression analysis, transcriptomics, proteomics and endocrinology. In this article we describe a pilot study to examine the feasibility, effectiveness and logistics of large-scale nationwide sample collection in Dutch families in which two or more sisters have given birth to spontaneous dizygotic twins. Pedigree data and addresses from family members of proband mothers were collected by telephone. Blood and urine samples were collected during a home visit, and handled in the afternoon. All participants were bled between 7 a.m. and 10 a.m. after overnight fasting. Blood samples of fertile women with a natural cycle were collected on the second, third or fourth day of their menstrual cycle. The effects of transportation and storage on blood quality, lipids, RNA with and without challenge, lymphocytes and other parameters were examined. Genomic DNA was isolated from blood and cells were immortalized using Epstein-Barr virus. In 78.6% of the women with a natural cycle blood samples were collected on the second, third or fourth day of the menstrual cycle. This percentage is likely to increase with the more dense geographical distribution of participants in the larger population. We conclude that the pilot study demonstrated the feasibility of this protocol to collect good quality of plasma, DNA, RNA and lymphocyte samples by home visits.

Nucleated red blood cells in concordant, appropriate-for-gestational age twins

OBJECTIVES

The purpose of this study was to test the hypothesis that neonatal nucleated red blood cell (RBC) counts are elevated in nondiscordant twins compared with singletons.

STUDY DESIGN

We compared absolute nucleated RBC counts taken after birth in 2 groups of term, appropriate-for-gestational age infants; 74 concordant twins, and 29 singleton control infants. We excluded infants with factors associated with a potential increase in absolute nucleated RBC counts.

RESULTS

Birth weight and gestational age were significantly lower in twins than in singletons (P < .01). Hematocrit, absolute nucleated RBC count, and corrected lymphocyte counts were significantly higher in twins (P < .01). In multiple regression, the significantly higher absolute nucleated RBC count in twins remained significantly higher even after taking into account gestational age and Apgar scores.

CONCLUSION

Concordant, appropriate-for-gestational age twins have increased nucleated RBCs at birth compared with singleton control infants.

Neonatal nucleated red blood cells in discordant twins

The objective of this study was to test the hypothesis that in discordant twins, the smaller infant has higher absolute nucleated red blood cell (RBC) count than the larger sibling. We compared absolute nucleated RBC counts, hematocrits, absolute leukocyte counts, absolute granulocyte counts, absolute lymphocyte counts, RBC counts and platelet counts obtained in the first 12 hours of life in 30 discordant twin sets. The smaller infant had a higher absolute nucleated red blood cell count and lower platelet counts than its larger sibling. Platelet counts correlated inversely with absolute nucleated RBC counts ( R(2) = 24.5%; p < 0.001) and absolute nucleated RBCs correlated directly with percent intertwin weight differences ( R(2) = 17.8%; p = 0.02). In discordant twins, the smaller infant has higher absolute nucleated RBC count and lower platelet counts than the larger sibling. We speculate that the hematologic alterations in the smaller fetus are linked to relative fetal hypoxia.

Size at Birth, Fasting Glucose and Insulin Levels and Insulin Resistance in Adult Twins

Studies in singletons have found an association between birthweight and Type 2 diabetes in adult life. The aim of this study was to investigate whether this association could also be seen in twins. 59 monozygotic (MZ) and 69 dizygotic (DZ) same-sex twin pairs aged 19-50 years and 89 singleton controls matched for age, gestational age, gender, maternal age and parity were recruited from a local obstetric database. Associations between adult glucose, HbA(1)C and insulin levels and insulin resistance and birthweight were assessed by linear regression with adjustment for confounding variables. Twins were significantly lighter at birth than singleton controls, but there were no significant differences in adult weight, glucose, HbA(1)C and insulin levels or insulin resistance between twins and controls. The relationship between birthweight and fasting glucose and insulin levels, and insulin resistance was not significantly different from zero in either twins or controls, but birthweight was significantly negatively associated with HbA(1)C only in controls. There was no evidence of a difference between MZ and DZ twins in unpaired or within-pair analysis. These results provide little evidence that low birthweight in twins increases the risk of impaired glucose-insulin metabolism in young adults or that genetic factors can account for the association observed in singletons.

Quantitative studies on the haptoglobin of apparently healthy adult male twins

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Blood groups in twin studies. Calculation of the probability of monozygosis

When calculating the chance of monozygosis from the results of a blood group study in a twin-family, it is desirable to use the complete information that is presented by these results and not only part of it.

A calculation-method in which the complete genetic-information is used is presented.

The use of the formulas is demonstrated by calculating the probability of monozygosis in two examples.