Estimation of individual genetic and environmental factor scores

Implicit in the application of the common-factor model as a method for decomposing trait covariance into a genetic and environmental part is the use of factor scores. In multivariate analyses, it is possible to estimate these factor scores for the communal part of the model. Estimation of scores on latent factors in terms of individual observations within the context of a twin/family study amounts to estimation of individual genetic and environmental scores. Such estimates may be of both theoretical and practical interest and may be provided with confidence intervals around the individual estimates. The method is first illustrated with stimulated twin data and next is applied to blood pressure data obtained in a Dutch sample of 59 male adolescent twin pairs. Subjects with high blood pressure can be distinguished into groups with high genetic or high environmental scores.

Using factor scores to detect G X E interactive origin of "pure" genetic or environmental factors obtained in genetic covariance structure analysis

Moment expressions for individual factor scores can serve as simple tests for the presence of a particular class of interaction factors that are disguised as pure genetic and/or environmental factors. That is, individual genetic and environmental factor scores may be used to construct fourth-order moments of these factors in order to test whether a common genetic or environmental factor in the multivariate genetic factor model is in fact of the interactive origin concerned. Expected fourth-order moments are derived for cases with and without interaction. Application of fourth-order moments of factor scores to detect interactive origin of common factors is illustrated with simulated twin data.

Comparison of spot and band impedance cardiogram electrodes across different tasks

Impedance cardiography has become of widespread interest as a noninvasive cardiovascular monitoring technique. This study compared the use of spot electrodes and two different types of band electrodes in the determination of systolic time intervals and stroke volume. EKG, impedance cardiogram, and phonocardiogram were recorded on 12 volunteers during rest, during a reaction time task, and after a short exercise task. Systolic time intervals (pre-ejection period and left ventricular ejection time) were computed on a beat-to-beat basis and on the ensemble-averaged signals. The only differences between spot and band electrodes were for impedance base level and electrode conductance. For stroke volume and the systolic time interval measures there were no differences between electrode arrays, nor were there any interactions with tasks. Correlations for stroke volume and systolic time interval measures as determined under different electrode conditions were around .8.

Resemblances of parents and twins in sports participation and heart rate

A model to analyze resemblances of twins and parents using LISREL is outlined and applied to sports participation and heart-rate data. Sports participation and heart rate were measured in 44 monozygotic and 46 dizygotic adolescent twin pairs and in their parents. Genetic factors influence variation in both sports behavior and heart rate, while there is no evidence for transmission from parental environment to offspring environment. For sports participation the data support a model in which there is a high positive correlation between environments of spouses and between environments of female twins. This correlation is absent for male twins and negative for opposite sex twins. For heart rate, a positive correlation between environmental influences was observed for all twins; there is no evidence for assortative mating. The proposed model can also handle data sets where parents and twins have been measured on more than one variable. This is illustrated by an application to the observed association of sports participation and heart rate.

Willingness to drive when drunk and personality: a twin study

In a laboratory study of psychomotor sensitivity to alcohol, twins were asked "Would you drive a car now?" at 1, 2, and 3 h after drinking a standard dose of ethanol (0.75 g/kg). Correlations among these binary items, the Eysenck personality scales, and age were investigated using PRELIS and LISREL. Willingness to drive and Extraversion correlate at all three times in both males and females. In males, willingness to drive also correlates with Psychoticism, and in females it correlates negatively with the Lie (or Social Desirability) scale. Most correlations between cotwins in willingness to drive were significant in both monozygotic (MZ) and dizygotic (DZ) male twins but correlations were lower in female twins. Factor and Markovian models were fitted. In males there seem to be both genetic and cultural influences on willingness to drive when drunk. About half the genetic variance seems to be the pleiotropic effects of genes influencing Extraversion. The correlations with Psychoticism, on the other hand, seem to be largely environmental in origin. The small sample size and lack of proper significance tests mean that these results must be interpreted with caution.

LISREL analysis of twin data with structured means

A method is introduced to test the hypothesis that both the phenotypic means and the phenotypic covariances can be modeled with the same common genetic and environmental factors. LISREL can be used to implement the method. An illustration is given with simulated twin data.

Does the heart know what the eye sees? A cardiac/pupillometric analysis of motor preparation and response execution

Autonomic response measures are well suited for the study of preparation because they allow the analysis of covert aspects of performance. This is illustrated by an experiment in which task-evoked cardiac and pupillary responses were compared during a disjunctive (Go/No Go) reaction task. The motoric demands of the task were varied by manipulating foreperiod length (4 and 8 s) and probability of response (25%, 50%, and 75%). Reaction time increased with foreperiod length and decreased with probability of response. The depth of anticipatory heart rate deceleration was affected only by foreperiod length. Analysis of the beats during, and directly preceding and following the imperative stimulus revealed that interbeat intervals increased with probability of responding and foreperiod duration. The effect of stimulus timing relative to the R-wave of the ECG was also analyzed. Early occurring stimuli prolonged the cycle of their occurrence more than late occurring stimuli. The cycle time effect was somewhat more pronounced for No Go stimuli than for Go stimuli. The subsequent cycle was shorter for early occurring stimuli compared to late stimuli. This effect was stronger for Go compared to No Go trials. Both Go and No Go reactions elicited significant pupil dilations. The No Go dilation peaked earlier than the Go dilation and its amplitude was smaller. Probability of responding affected the latency of the No Go dilation but not that of the Go dilation. The current results justify an interpretation of preparation in terms of a timing mechanism (indexed by heart rate deceleration during the foreperiod) and a mechanism allocating processing resources to stimulus encoding (indexed by cardiac slowing just prior to stimulus occurrence) and response preparation (indexed by continued cardiac deceleration and pupillary dilation).

Factor and simplex models for repeated measures: application to two psychomotor measures of alcohol sensitivity in twins

As part of a larger study, data on arithmetic computation and motor coordination were obtained from 206 twin pairs. The twins were measured once before and three times after ingesting a standard dose of alcohol. Previous analyses ignored the time-series structure of these data. Here we illustrate the application of simplex models for the genetic analysis of covariance structures in a repeated-measures design and compare the results with factor models for the two psychomotor measures. We then present a bivariate analysis incorporating simplex processes common and specific to the two measures. Our analyses confirm the notion that there is genetic variation affecting psychomotor performance which is "switched on" in the presence of alcohol. We compare the merits of analysis of mean products versus covariance matrices and confront some practical problems that may arise in situations where the number of subjects is relatively small and where the causal structure among the latent variables places a heavy demand on the data.

Twin studies on urinary pepsinogen A phenotypes and serum pepsinogen A levels

Urinary pepsinogen A (PGA or PG I) phenotypes and serum PGA levels were studied in MZ and DZ twins and their parents. In 45 out of 48 MZ twin pairs PGA patterns were completely identical, while 3 MZ twin pairs showed minor differences in the relative intensity of the Pg5 isozymogen. This suggests that the intensity of this isozymogen may be influenced by nongenetic factors. There was little difference in the interclass correlations of serum PGA levels between MZ and DZ twins, indicating a large contribution of common environmental factors to serum PGA levels. This is in contrast with previous studies.

Constrained maximum likelihood analysis of familial resemblance of twins and their parents

When the univariate twin design is extended by including parents of twins, it is possible to assess additive genetic effects in the presence of assortative mating and genotype-environment correlation, the effects of parental influence, as well as the extent of residual shared environmental influences. The analysis of data obtained in such an extended twin design can be carried out by means of constrained maximum likelihood confirmatory factor analysis. Specifically, the structural model underlying this design can be represented as a LISREL model with nonlinear constraints. This representation offers the possibility to consider extended multivariate twin designs involving common genetic and environmental factors. The proposed method will be illustrated with applications to simulated and real data.

Spectral analysis of twin time series designs

The genetic analysis of physiological time series has to accommodate the presence of autocorrelation. This can be accomplished by means of orthogonal transformation of the series, thus enabling the use of standard genetic analysis techniques for the sequence of uncorrelated transforms. In view of the oscillatory character which typifies various physiological time series, it is customary to invoke spectral techniques for the analysis of these series. It can be shown that spectral analysis is an orthogonal transformation that asymptotically resembles principal component analysis. Consequently, standard genetic analysis methods for the uncorrelated spectral transforms may be used. This approach will be illustrated with simulated and real (heart rate) data for univariate twin time series. Furthermore, it will be indicated that the proposed analysis can be readily generalized to multivariate time series.

[Incidence of cheilognathopalatoschisis in the Netherlands]

Until now, data on the incidence of cleft lip and/or palate in the Netherlands are scarcely available. For this study data were used from the National Medical Registration (NMR) and the National Obstetric Registration (NOR) over the years 1982 and 1983. Only children born in a general hospital have been registered. In the years 1982 and 1983 the NMR registered 295 children with the malformation just mentioned. The incidence calculated from these figures is between 1,38 and 1,77. The age distribution of mothers with a child with a cleft lip and/or palate (CLP) was compared to the total group of mothers. No correlations were found between the age of the mother and the birth of a CLP-child. The necessity of an accurate registration of congenital malformations in general in the Netherlands is emphasized.