DeFries-Fulker analysis of longitudinal reading performance data from twin pairs ascertained for reading difficulties and from their nontwin siblings

A sibling-comparison study of smoking during pregnancy and risk for reading-related problems

This research examines the relationship between smoking during pregnancy (SDP) and risk for reading related problems in siblings discordant for exposure to SDP. Data (N = 173 families) were drawn from the Missouri Mothers and Their Children study, a sample, identified using birth records (years 1998-2005), in which mothers changed her smoking behavior between two pregnancies (Child 1 [older sibling]: M = 12.99; Child 2 [younger sibling]: M = 10.19). A sibling comparison approach was used, providing a robust test for the association between SDP and reading related outcomes in school-aged children. Results suggested within-family (i.e., potentially causal) associations between SDP and reading and language/comprehension factor scores, as well as between SDP and specific reading-related skills, including reading accuracy and receptive language, with increased exposure to SDP associated with decreased performance. SDP was not associated with spelling, reading rate, or receptive vocabulary. Initial within-family associations between SDP and word-letter identification, phonetic/decoding skills, and reading comprehension were fully attenuated following partial control for genetic and environmental confounding of the associations. These findings indicate that exposure to SDP is associated with poorer performance on some, but not all skills assessed.

Predicting vocabulary growth in children with and without specific language impairment: a longitudinal study from 2;6 to 21 years of age

PURPOSE

Children with specific language impairment (SLI) often have vocabulary impairments. This study evaluates longitudinal growth in a latent trait of receptive vocabulary in affected and unaffected children ages 2;6 (years;months) to 21 years and evaluates as possible predictors maternal education, child gender, and nonverbal IQ.

METHOD

A sample of 519 participants (240 with SLI; 279 unaffected) received an average of 7 annual assessments for a total of 3,012 latent trait Peabody Picture Vocabulary Test (PPVT) observations. Unconditional and conditional multilevel growth models were estimated to evaluate growth trajectories and predictor relationships over time.

RESULTS

Children with SLI had lower levels of receptive vocabulary throughout the age range assessed. They did not close the gap with age peers. Children with higher nonverbal IQs had better PPVT performance, as did children of mothers with higher education. Child gender showed an advantage for young girls that leveled out with age and then became an advantage for boys from ages 10 to 21 years. All children's rate of vocabulary acquisition slowed around 12 years of age.

CONCLUSIONS

The outcomes of the study have implications for hypothesized causal pathways for individual differences; predictions differ for children under 5 years, 6-10 years, and later ages.

Word reading fluency: role of genome-wide single-nucleotide polymorphisms in developmental stability and correlations with print exposure

The genetic effects on individual differences in reading development were examined using genome-wide complex trait analysis (GCTA) in a twin sample. In unrelated individuals (one twin per pair, n = 2,942), the GCTA-based heritability of reading fluency was ~20%-29% at ages 7 and 12. GCTA bivariate results showed that the phenotypic stability of reading fluency from 7 to 12 years (r = 0.69) is largely driven by genetic stability (genetic r = 0.69). Genetic effects on print exposure at age 12 were moderate (~26%) and correlated with those influencing reading fluency at 12 (genetic r = 0.89), indicative of a gene-environment correlation. These findings were largely consistent with quantitative genetic twin analyses that used both twins in each pair (n = 1,066-1,409).

Intensive Reading Remediation in Grade 2 or 3: Are There Effects a Decade Later?

Despite data supporting the benefits of early reading interventions, there has been little evaluation of the long-term educational impact of these interventions, with most follow-up studies lasting less than two years (Suggate, 2010). This study evaluated reading outcomes more than a decade after the completion of an 8-month reading intervention using a randomized design with second and third graders selected on the basis of poor word-level skills (Blachman et al., 2004). Fifty-eight (84%) of the original 69 participants took part in the study. The treatment group demonstrated a moderate to small effect size advantage on reading and spelling measures over the comparison group. There were statistically significant differences with moderate effect sizes between treatment and comparison groups on standardized measures of word recognition (i.e., Woodcock Basic Skills Cluster, d = 0.53; Woodcock Word Identification, d = 0.62), the primary, but not exclusive, focus of the intervention. Statistical tests on other reading and spelling measures did not reach thresholds for statistical significance. Patterns in the data related to other educational outcomes, such as high school completion, favored the treatment participants, although differences were not significant.

Rethinking ADHD and LD in DSM-5: proposed changes in diagnostic criteria

The Diagnostic and Statistical Manual of Mental Disorders (DSM) is currently undergoing revision that will lead to a fifth edition (DSM-5) in 2013. This article first provides a brief synopsis of the DSM-5 administrative structure, procedures, and guiding principles to enhance understanding of how changes are made in the DSM. The next two sections (on attention-deficit/hyperactivity disorder and learning disorders, respectively) highlight the major concerns and controversies surrounding the DSM-IV diagnostic criteria for these two disorders and provide a rationale for the proposed changes to the criteria, along with a commentary on the empirical evidence on which the proposed changes were based.

Multiple regression analysis of reading performance data from twin pairs with reading difficulties and nontwin siblings: the augmented model

The augmented multiple regression model for the analysis of data from selected twin pairs was extended to facilitate analyses of data from twin pairs and nontwin siblings. Fitting this extended model to data from both selected twin pairs and siblings yields direct estimates of heritability (h2) and the difference between environmental influences shared by members of twin pairs and those of sib or twin-sib pairs (i.e., c2(t) - c2 (s)). When this model was fitted to reading performance data from 293 monozygotic and 436 dizygotic pairs selected for reading difficulties, and 291 of their nontwin siblings, h2 = .48 ± .22, p = .03, and c2 (t) - c2 (s) = .22 ± .12, p = .06. Although the test for differential shared environmental influences is only marginally significant, the results of this analysis suggest that environmental influences on reading performance that are shared by members of twin pairs (.36) may be substantially greater than those for less contemporaneous twin-sibling pairs (.14).

Genetic and environmental etiologies of reading difficulties: DeFries-Fulker analysis of reading performance data from twin pairs and their nontwin siblings

Reading performance data from 254 pairs of identical (MZ) and 420 pairs of fraternal (DZ) twins, 8.0 to 20.0 years of age, were subjected to multiple regression analyses. An extension of the DeFries-Fulker (DF) analysis (DeFries & Fulker, 1985, 1988) that facilitated inclusion of data from 303 of their nontwin siblings was employed. In addition to providing estimates of heritability, this analysis yields a test of the difference between shared environmental influences for twins versus siblings (Astrom et al., 2011). Results suggest that proband reading deficits are due substantially to genetic factors (.67 ± .07, p < .001), and that shared environmental influences are significantly higher for members of twin pairs than for those of twins and their nontwin siblings (viz., .25 versus .17, p = .02).

Mutation of the dyslexia-associated gene Dcdc2 impairs LTM and visuo-spatial performance in mice

Developmental reading disorder (RD) affects 5-10% of school aged children, with a heritability of approximately 60%. Genetic association studies have identified several candidate RD susceptibility genes, including DCDC2; however, a direct connection between the function of these genes and cognitive or learning impairments remains unclear. Variants in DCDC2, a member of the doublecortin family of genes, have been associated in humans with RD and ADHD and Dcdc2 may play a role in neuronal migration in rats. In this study, we examined the effect of Dcdc2 mutation on cognitive abilities in mice using a visual attention and visuo-spatial learning and memory task. We show that both heterozygous and homozygous mutations of Dcdc2 result in persistent visuo-spatial memory deficits, as well as visual discrimination and long-term memory deficits. These behavioral deficits occur in the absence of neuronal migration disruption in the mutant mice, and may be comorbid with an anxiety phenotype. These are the first results to suggest a direct relationship between induced mutation in Dcdc2 and changes in behavioral measures. Dcdc2 mutant mice should prove useful in future studies designed to further dissect the underlying neural mechanisms that are impaired following Dcdc2 mutation.