Catherine Derom

INCREASED MONOZYGOTIC TWINNING RATE AFTER OVULATION INDUCTION

Multiple births after artificial induction of ovulation (AIO) are usually considered to be due to fertilisation of multiple ova. In the East Flanders Prospective Twin Study between 1978 and 1985 the frequency of zygotic splitting after AIO (1.2%) was significantly higher than the expected frequency (0.45%) among spontaneous twins and triplets. Moreover, after AIO the frequency of zygotic division was significantly higher in triplets than in twins. AIO seems to be the first identified biological mechanism influencing the monozygotic twinning rate.

A momentary assessment study of the relationship between affective and adrenocortical stress responses in daily life

The tendency to experience negative emotions in the face of stress may lead to repeated overactivation of the hypothalamic-pituitary-adrenal axis. In a sample of 556 women, this study used the Experience Sampling Method to assess different daily stressors, current mood, and salivary cortisol, 10 times daily for 5 days. Multilevel analyses estimated the contributions of stressors and mood states as predictors of salivary cortisol secretion. Results showed that minor stressors were associated with decreased positive affect and increased negative affect, agitation, and cortisol. Of the mood states, only negative affect was independently associated with cortisol. Negative affect also mediated effects of daily stressors on cortisol. Although further research is needed to clarify: (i) the causal pathways between daily stress, mood, and cortisol and (ii) the importance of daily stress reactivity as a prospective risk factor, these findings confirm that minor daily stressors can influence emotional and biological processes involved in subjective well-being.

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.

Transition from stress sensitivity to a depressive state: longitudinal twin study

BACKGROUND Daily-life stress sensitivity is associated with depression, but prospective data are lacking. AIMS To examine associations between baseline ecological daily-life stress sensitivity and later depression, and to identify genetic and non-genetic factors moderating the transition from stress sensitivity to depression. METHOD Daily-life stress sensitivity was assessed at baseline in twins (n = 502). One baseline and four follow-up measurements of depressive symptoms and negative life events were collected, as well as interview-based diagnoses at baseline and last follow-up. Hypothesised genetic markers were determined. RESULTS Baseline stress sensitivity was associated with increased depressive symptoms at follow-up and risk of major depressive disorder. Both genetic liability and major life events moderated the probability of transition from stress sensitivity to depression. CONCLUSIONS Onset of depression is attributable to pre-onset ecological measurements of stress sensitivity, particularly where genetic liability is high and individuals have reached a stage where the influence of competing environmental causes is low.

A prospective twin study of birth weight discordance and child problem behavior

BACKGROUND We investigated whether low birth weight constitutes a causal risk factor for child problem behavior, using a variation of the co-twin control method. METHODS In a representative sample of 745 twin pairs (monozygotic: 324 pairs), birth weight was recorded at birth and child problem behavior at mean age 10 years was measured with the Child Behaviour Checklist (CBCL). RESULTS Lower birth weight was a continuous risk factor for later child problem behavior (adjusted regression coefficient over units of 500 g: beta = -.15, p =.046), and greater levels of within-pair CBCL discordance did not result in a reduced effect size. Greater within-pair birth weight discordance was associated with greater within-pair CBCL score discordance (beta =.35, p <.001). This latter effect was similar in monozygotic (beta =.34, p =.005) and dizygotic twins (beta =.37, p =.003). CONCLUSIONS The fact that (1) the effect size of the association between low birth weight and child problem behavior was not reduced in pairs with greater levels of CBCL discordance, and (2) similar effect sizes were found in monozygotic and dizygotic twins for the within-pair association between birth weight discordance and CBCL score discordance, suggests that the observed relationship between low birth weight and child problem behavior is not due to a shared environmental or genetic variable that influences both characteristics. Lower birth weight is a causal risk factor for child problem behavior, the effects of which may well extend into adulthood.

FKBP5 as a possible moderator of the psychosis-inducing effects of childhood trauma

BACKGROUND FK506 binding protein 5 (FKBP5) has repeatedly been shown to be a critical determinant of post-traumatic stress disorder (PTSD) and depression following childhood trauma. AIMS To examine the role of FKBP5-trauma interactions in the partly stress-related psychosis phenotype. METHOD In 401 general population twins, four functional polymorphisms were examined in models of psychosis and cortisol, and followed up in models of psychosis in three samples at different familial liability (175 controls, 200 unaffected siblings and 195 patients with a psychotic disorder). RESULTS The most consistent finding was an interaction between childhood trauma and rs9296158/rs4713916 on psychotic symptoms and cortisol in the twin sample, combined with a directionally similar interaction in siblings (rs4713916) and patients (rs9296158), A-allele carriers at both polymorphisms being most vulnerable to trauma. CONCLUSIONS Trauma may increase the risk of psychosis through enduring changes in the cortisol feedback loop, similar to that for PTSD, suggesting comparable biological mechanisms for psychosis across diagnostic boundaries.

Meeting risk with resilience: high daily life reward experience preserves mental health

Geschwind N, Peeters F, Jacobs N, Delespaul P, Derom C, Thiery E, van Os J, Wichers M. Meeting risk with resilience: high daily life reward experience preserves mental health.

Zygosity determination in newborn twins using DNA variants.

A prerequisite for the optimal use of the twin method in human genetics is an accurate determination of the zygosity at birth. This diagnosis is sometimes hampered by the lack of available specific markers. We report here the use of DNA variants (restriction fragment length polymorphisms) as genetic markers for zygosity determination. We have analysed the placental DNA of 22 twin pairs with known zygosity on Southern blots by hybridisation with polymorphic human DNA probes. We looked at six different polymorphic sites using four restriction enzymes and six DNA probes. Among 10 dizygotic (DZ) pairs, only one was not demonstrably different and seven had at least two discordances. Within each of the 12 monozygotic (MZ) pairs there was complete concordance. Thus, nine of 10 dizygotic and 12 of 12 monozygotic twins were assigned their correct zygosity solely by comparison of six DNA variants. The use of these highly polymorphic DNA probes may have practical importance for antenatal diagnosis and paternity testing.

Lack of evidence for the role of human adenovirus-36 in obesity in a European cohort.

Adenovirus infection has been shown to increase adiposity in chickens, mice, and nonhuman primates. Adenovirus type 36 (Ad‐36) DNA was detected in adipose tissues in these animal trials. In the United States, Ad‐36 significantly correlates with obesity as illustrated by an Ad‐36 seroprevalence of 30% in obese individuals and 11% in nonobese individuals. We investigated the possibility of a similar correlation of Ad‐36 in Dutch and Belgian persons. In total, 509 serum samples were analyzed for Ad‐36 antibodies using a serum neutralization assay. In addition, PCR was used to detect adenoviral DNA in visceral adipose tissue of 31 severely obese surgical patients. Our results indicated an overall Ad‐36 seroprevalence of 5.5% increasing with age. BMI of Ad‐36 seropositive humans was not significantly different from seronegative humans. No adenoviral DNA could be found using PCR on visceral adipose tissue. In conclusion, this first Ad‐36 study in the Netherlands and in Belgium indicates that Ad‐36 does not play a role as a direct cause of BMI increase and obesity in humans in Western Europe.

Birthweight in liveborn twins: the influence of the umbilical cord insertion and fusion of placentas

Objective To assess the relation of umbilical cord insertion and fusion of placentas with birthweight in monozygotic monochorionic, monozygotic dichorionic, and dizygotic twins.