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J C DeFries

Publications and source records attributed to J C DeFries.

At least 19 recordsLinked to original sources
PubMed1992

Attention deficit disorder in reading-disabled twins: evidence for a genetic etiology.

In order to assess the genetic etiology of attention deficit hyperactivity disorder (ADHD), the basic regression model for the analysis of selected twin data (DeFries & Fulker, 1985, 1988) was fitted to questionnaire data (DICA: Diagnostic Interview for Children and Adolescents; Herjanic, Campbell, & Reich, 1982) for 37 identical and 37 fraternal twin pairs tested in the Colorado Reading Project. Results of this analysis suggest that ADHD is highly heritable. Moreover, adjusting DICA scores for either IQ or reading performance differences did not substantially change parameter estimates. In future analyses of larger data sets, distinguishing between possible subtypes of attentional problems (e.g., ADD with or without hyperactivity) may facilitate tests of more searching etiological questions.

Achievement↗
PubMed1992

Multiple regression analysis of twin data: a model-fitting approach.

The multiple regression methodology proposed by DeFries and Fulker (DF; 1985, 1988) for the analysis of twin data is compared with maximum-likelihood estimation of genetic and environmental parameters from covariance structure. Expectations for the regression coefficients from submodels omitting the h2 and c2 terms are derived. Model comparisons similar to those conducted using maximum-likelihood estimation procedures are illustrated using multiple regression. Submodels of the augmented DF model are shown to yield parameter estimates highly similar to those obtained from the traditional latent variable model. While maximum-likelihood estimation of covariance structure may be the optimal statistical method of estimating genetic and environmental parameters, the model-fitting approach we propose is a useful extension to the highly flexible and conceptually simple DF methodology.

Aptitude↗
PubMed1992

Mapping quantitative trait loci for behavioral traits in the mouse.

After many years of studying various behavioral characters in the mouse, it is clear that most are heritable and are specified by complexes of genes or quantitative trait loci (QTLs). In order to attain a more complete understanding of the genetic causes of individual differences in behavior, the mechanism of action of these QTLs must be elucidated. The most straightforward approach to determining the mechanism of action of a particular QTL is to identify and molecularly clone the gene; this can be done by positional cloning, which depends on precise knowledge of the genetic map position. As the genetic data base for the mouse genome continues to develop, such strategies will become increasingly easy to perform. Here we suggest a multistage strategy for QTL mapping using recombinant-inbred strains of mice: (1) characterize genomic DNA from parental strains originally used to generate the RI strains; (2) characterize the RI strains for a quantitative character and for DNA markers that differ in the parental strains; and (3) assess the quantitative character in F2 mice derived from crosses between the parental strains, then determine the genotypes of extreme F2 mice for markers that account for at least 5% of the additive genetic variance. Data from these F2 crosses can be used to test hypotheses from the analysis of RI strains, i.e., that a QTL maps to a particular region. Using data from the mouse genome data base, this strategy should allow the molecular identification of the gene based on a candidate-gene approach. We illustrate the approach with examples from our work in mapping QTLs specifying neural sensitivity to the anesthetic effects of ethanol.

Alcoholism↗
PubMed1992

Differential heritability across levels of cognitive ability.

Differences in heritability and shared environmentality across levels of cognitive ability were assessed in a sample of 264 twin pairs tested at 1 year of age and in subsets tested at 2 and 3 years. Using an extension of the DF multiple regression methodology for analyzing twin data, no evidence was found for a linear or quadratic effect of level of cognitive ability on estimates of heritability or shared environmentality.

Aptitude↗
PubMed1992

Quantitative genetic analysis of IQ development in young children: multivariate multiple regression with orthogonal polynomials.

The study of psychological development has recently benefited from innovative analytic methods for estimating and examining the correlates of individual growth curves. These methods are more consistent with a conceptualization of development as an ongoing, continuous process, rather than as increases or decreases in a trait between two discrete time points. Recent developmental behavior genetic models have focused on continuity and change in the genetic and environmental influences underlying phenotypes. In contrast, we present a model for genetic and environmental influences on phenotypic development per se. In this model, we adapted multiple regression methods developed for twin designs (DeFries and Fulker, 1985) to a parent-offspring adoption design and to a multivariate framework in which repeated measurements are decomposed into orthogonal polynomial trends. We applied these analyses to the development of IQ during infancy and early childhood using parent-offspring data from adoptive and nonadoptive families in the Colorado Adoption Project. The results suggested familial environmental influences on children's mean IQ for ages 1-4 but environmental influences specific to fathers' cognitive ability on children's IQ development. We also discuss advantages and disadvantages of the multivariate multiple regression method for studying genetic and environmental influences on development.

Adoption↗
PubMed1992

Confirmatory factor analysis of reading and mathematics performance: a twin study.

Reading and mathematics performance data from a sample of 264 reading-disabled twin pairs and 182 matched control twin pairs were subjected to multivariate behavior genetic analysis. The factor structure of reading and math performance measures was found to be highly similar for both groups. Consistent with previous findings obtained using alternative methods, a significant heritable component to individual differences in reading performance was found both within the reading-disabled (h2 = 0.78) and control (h2 = 0.74) twin samples. In addition, a substantial genetic influence on mathematics performance was found (h2 = 0.51 and 0.60 in the reading-disabled and control samples, respectively), although shared environmental influences common to both members of a twin pair also contribute significantly to the variance in math scores of both groups (c2 = 0.44 and 0.37). Moreover, genetic influences accounted for 98% of the observed correlation between reading and math performance within the sample of reading-disabled twin pairs, and for 55% of the observed correlation in the control sample. Thus, individual differences in both reading and mathematics performance are highly heritable and appear to be caused by many of the same genetic influences.

Adolescent↗
PubMed1992

A twin study of the etiology of comorbidity: attention-deficit hyperactivity disorder and dyslexia.

Monozygotic and dizygotic twin pairs, in which at least one member of each pair is reading disabled (RD), were assessed for attention-deficit hyperactivity disorder (ADHD). Within pair cross-concordances of the RD and ADHD qualitative diagnoses for monozygotic twins were larger than for dizygotic twins, although not significantly so (p less than 0.10). Thus, the data suggest that RD and ADHD may be primarily genetically independent. However, trends in the data and subtype analyses suggest that in some cases RD and ADHD may occur together because of a shared genetic etiology and that a genetically mediated comorbid subtype may exist.

Achievement↗
PubMed1992

Gender ratios among reading-disabled children and their siblings as a function of parental impairment.

Gender ratios are reported for 374 reading-disabled probands and their 530 siblings included in five independent studies of reading disability. Ratios were tabulated for each study as a function of parental impairment (neither parent affected, mother only affected, father only affected, and both parents affected). Results reveal a small excess of male probands in referred and clinic samples of reading-disabled children, but not in research-identified samples. Gender ratios among siblings of reading-disabled probands are approximately 1:1. In addition, combined results indicate that gender ratios of neither probands nor their siblings vary substantially as a function of parental impairment.

Adult↗
PubMed1992

The external validity of age- versus IQ-discrepancy definitions of reading disability: lessons from a twin study.

Recent research has raised the question of whether age- and IQ-discrepancy forms of reading disability (RD) are distinguishable in terms of either their underlying linguistic deficit or their response to treatment, thus threatening the external validity of the traditional distinction between specific reading retardation and reading backwardness. The present study pursued the external validity of this distinction in three domains: (a) genetic etiology, (b) sex ratio and clinical correlates, and (c) neuropsychological profiles. Each of these domains was explored in the RD (n = 640) and control (n = 436) twins participating in the Colorado Reading Project (514 males, 562 females, with an overall mean age of 12.42 years). Little evidence for external validity was found in terms of the clinical correlates of attention deficit-hyperactivity disorder (ADHD), immune disorders, or handedness. Most importantly, there was no evidence of differential genetic etiology of the two phenotypes in this sample, in that deficits in both phenotypes were similarly heritable (h2g = .40 and .46 for age and IQ phenotypes, respectively) and the genetic correlation between them was high (rG = .88 to .96). However, the genetic and neuropsychological profile analyses did suggest that age- and IQ-discrepancy definitions of RD may relate differentially to component reading processes, such as phonological awareness and orthographic coding.

Attention Deficit Disorder with Hyperactivity↗
PubMed1991

Evidence for major gene transmission of developmental dyslexia.

OBJECTIVE: --There is strong evidence that developmental dyslexia is both familial and heritable, but the mode of genetic transmission has remained unclear. In this article, we examine specific genetic hypotheses about the mode of transmission of developmental dyslexia by performing complex segregation analyses. DESIGN: --A family study method was applied, whereby the relatives of dyslexic probands were examined for dyslexia. The families studied represent four independently ascertained samples. SETTING: --The four samples of families were primarily from rural and suburban communities of Colorado, Washington State, and Iowa. PARTICIPANTS: --A total of 204 families and 1698 individuals in the four samples combined. MAIN OUTCOME MEASURES: --The complex segregation program, POINTER, was used to test competing genetic hypotheses of how a categorical trait (dyslexia) is transmitted in families. RESULTS: --The results were consistent with major locus transmission in three of four samples and with polygenic transmission in the fourth. In these three samples, the estimates of penetrance for the AA, Aa, and aa genotypes (where A is the abnormal allele) were, respectively, 1.000, 1.000, and 0.001 to 0.039 in males, and 0.560 to 1.000, 0.550 to 0.897, and 0.000 in females. The estimated gene frequency of the major locus was between 3% and 5%. CONCLUSIONS: --Sex-influenced, additive, or dominant transmission occurs in a significant proportion of dyslexic families. Other evidence indicates, however, that dyslexia is etiologically heterogeneous and that there is genetic heterogeneity even among families selected for apparent dominant transmission. Thus, while no single major locus may account for all of dyslexia, it is important to pursue potential major loci for dyslexia using linkage techniques.

Adult↗
PubMed1991

Parent-offspring and sibling adoption analyses of parental ratings of temperament in infancy and childhood.

A first step toward understanding the etiology of personality is to investigate the relative impact of genetic and environmental factors using twin and adoption designs. Twin studies of infants and young children indicate substantial genetic influence for parental ratings of temperament in the preschool years. Adoption studies, however, have not previously been reported during the early years of life. We present parent-offspring comparisons for temperament (emotionality, activity, sociability, and impulsivity) for adopted and nonadopted children yearly from 1 to 7 years of age and their biological, adoptive, and nonadoptive parents. Also presented are correlations for adoptive and nonadoptive siblings when each child was 1, 2, 3, and 4 years of age. In contrast with twin results, little evidence is found for genetic influence. The average correlation between biological parents and their adopted-away children for data averaged over the 7 years is only .03. Similarly, the average parent-offspring correlation in nonadoptive families (.08) is no greater than in adoptive families (.12). Results for nonadoptive and adoptive siblings also indicate little genetic influence. The difference between the twin and adoption results may be due to environmental effects or to nonadditive genetic variance.

Adoption↗
PubMed1989

Multivariate path analysis of specific cognitive abilities in the Colorado Adoption Project: conditional path model of assortative mating.

A multivariate path model of genetic and environmental transmission employing a conditional path representation of assortative mating was fitted to specific cognitive abilities data from the Colorado Adoption Project and evaluated using a maximum-likelihood estimation procedure. In agreement with results obtained from a previous analysis of a smaller data set, significant genetic covariation among the cognitive variables was indicated and evidence for a general genetic factor was found. However, cultural transmission parameters are nonsignificant and environmental correlations among the measures are relatively small.

Adoption↗
PubMed1989

LS X SS recombinant inbred strains of mice: initial characterization.

In order to assess the genetic correlates of differences in ethanol-induced anesthesia, a set of 27 recombinant inbred (RI) strains was derived from an initial cross of the "long-sleep" (LS) and "short-sleep" (SS) selected lines of mice. In generations F24 and F25, samples of 534 and 580 mice from the LSXSS RI strains were tested for fall time, sleep time, and blood ethanol at awakening subsequent to intraperitoneal injection of a 4.1-g/kg body weight dose of ethanol. Approximately 2 weeks later, mice from F24 were also tested for body temperature lowering and blood-ethanol elimination rate (beta 60). Differences among the average ethanol-induced sleep-time scores of the RI strains are large (ranging from 36 to 171 min) and account for over 50% of the observed variance. Effects due to generation, sex, litters within strains, and the interaction between strain and generation are also significant, but account for relatively small proportions of the total variance. Quantitative genetic analyses of these data suggest that differences in sleep-time scores are polygenic; however, allelic differences at the albino (c) locus may have a pleiotropic effect. Genetic correlations between sleep time and blood ethanol at awakening (-0.79) and between body temperature 60 min after injection and beta 60 (+0.48) are significant. Because differences among the LSXSS RI strains are large and highly reliable, they should be valuable animal models for testing more searching hypotheses about the etiology of individual differences in ethanol-induced anesthesia.

Animals↗
PubMed1979

Multivariate behavioral genetic analysis of twin data on scholastic abilities.

Multivariate behavioral genetic analyses may employ either genetic and environmental correlations or phenotypically standardized covariances to assess the structure of genetic and environmental influences. Correlations and phenotypically standardized covariances answer different questions--correlations are appropriate for understanding the nature of genetic and environmental influences, whereas covariances are appropriate for determining the etiology of phenotypic correlations. The ratio of the genetic and environmental covariances to the phenotypic correlation yields estimates of bivariate heritability and environmentality, measures of the extent to which observed phenotypic covariance is due to genetic and environmental influences. Multivariate analyses of genetic and environmental correlations and covariances are illustrated with twin data on scholastic abilities. Factor analyses of correlations suggest that the same set of genes affects the major areas of academic achievement and that the environmental influences are similarly structured. Analyses of phenotypically standardized covariances indicate that the structures of genetic and environmental influences as they contribute to phenotypic resemblance among scholastic abilities are both similar and simple: there are one general genetic factor and one general environmental factor. Bivariate heritabilities and environmentalities are similar in magnitude, indicating that the strong phenotypic relationship among scholastic abilities is due roughly equally o genetic and environmental influences.

Analysis of Variance↗