The heritability of general cognitive ability increases linearly from childhood to young adulthood.

Although common sense suggests that environmental influences increasingly account for individual differences in behavior as experiences accumulate during the course of life, this hypothesis has not previously been tested, in part because of the large sample sizes needed for an adequately powered analysis. Here we show for general cognitive ability that, to the contrary, genetic influence increases with age. The heritability of general cognitive ability increases significantly and linearly from 41% in childhood (9 years) to 55% in adolescence (12 years) and to 66% in young adulthood (17 years) in a sample of 11 000 pairs of twins from four countries, a larger sample than all previous studies combined. In addition to its far-reaching implications for neuroscience and molecular genetics, this finding suggests new ways of thinking about the interface between nature and nurture during the school years. Why, despite life's 'slings and arrows of outrageous fortune', do genetically driven differences increasingly account for differences in general cognitive ability? We suggest that the answer lies with genotype-environment correlation: as children grow up, they increasingly select, modify and even create their own experiences in part based on their genetic propensities.

Differential genetic etiology of reading difficulties as a function of IQ: an update.

In order to test the hypothesis that the genetic etiology of reading disability differs as a function of IQ, composite reading performance data from 308 pairs of identical (monozygotic, MZ) twins and 440 pairs of fraternal (dizygotic, DZ) twins (254 same-sex and 186 opposite-sex) in which at least one member of each pair was classified as reading-disabled were subjected to multiple regression analysis (DeFries and Fulker, Behav Genet 15:467-473, 1985; Acta Genet Med Gemellol 37:205-216, 1988). In the total sample, heritability of the group deficit in reading performance (h(g)(2)) was .61 (±.06). However, results of fitting an extended regression model to reading performance and IQ data suggested that the genetic etiology of reading disability differs as a linear function of IQ (p ≤ .04). When the basic regression model was fitted separately to data from twin pairs with Wechsler (Examiner's manual: Wechsler intelligence scale for children-revised, 1974; Examiner's manual: Wechsler adult intelligence scale-revised, 1981) Full Scale IQ scores in the upper and lower 25% of the sample, resulting estimates of h(g)(2) were .75 (±.12) and .50 (±.10), respectively (p ≤ .045). These results suggest that reading difficulties in children with a higher IQ are due substantially to genetic influences and may require intensive remediation efforts.

Cloud droplet deposition in subalpine balsam fir forests: hydrological and chemical inputs.

Subalpine forests of the northern Appalachians are subject to significant deposition of water and chemicals via cloud droplet impaction. This deposition has been estimated by a method linking micrometeorological measures of turbulent transfer, a detailed representation of canopy structure, and experimentally derived capture efficiencies. Water inputs from clouds are about 46 percent, and chemical inputs range from 150 to 430 percent of the bulk precipitation.

A comparison of the cognitive deficits in reading disability and attention-deficit/hyperactivity disorder.

This study used a nonreferred sample of twins to contrast the performance of individuals with reading disability (RD; n = 93), attention-deficit/hyperactivity disorder (ADHD; n = 52), RD and ADHD (n = 48), and neither RD nor ADHD (n = 121) on measures of phoneme awareness (PA) and executive functioning (EF). Exploratory factor analysis of the EF measures yielded underlying factors of working memory, inhibition, and set shifting. Results revealed that ADHD was associated with inhibition deficits, whereas RD was associated with significant deficits on measures of PA and verbal working memory. The RD + ADHD group was most impaired on virtually all measures, providing evidence against the phenocopy hypothesis as an explanation for comorbidity between RD and ADHD.

Dyslexic and normal readers' eye movements.

Dyslexic and normal readers' eye movements were compared while tracking a moving fixation point and in reading. Contrary to previous reports, the dyslexic and normal readers did not differ in their number of saccades, percentage of regressions, or stability of fixations in the tracking task. Thus, defective oculomotor control was not associated with or a causal factor in dyslexia, and the dyslexics' abnormal eye movements in reading must be related to differences in higher cognitive processes. However, individual differences in oculmotor efficiency, independent of reading ability, were found within both the dyslexic and normal groups, and these differences were correlated in reading and tracking tasks.

Genetic and environmental influences on orthographic and phonological skills in children with reading disabilities.

Data from identical and fraternal twins were analyzed to estimate the proportions of genetic and environmental influences on group deficits in accuracy and, when available, speed for printed word recognition and for related skills in phonological decoding (PD), orthographic coding (OC), and phoneme awareness (PA). In addition, bivariate genetic analyses were employed to estimate the degree of common genetic influence on group deficits across these different reading and language skills. About half of the group deficits in each of the skills were due to genetic influences, and the genetic origins were largely shared among the measures (r(g) = .53 - .99), except for those between OC and PA (r(g) = .28 - .39). Implications of the results are discussed for models of reading disability and remediation.

Eye fixation patterns among dyslexic and normal readers: effects of word length and word frequency.

Eye fixation patterns of 21 dyslexic and 21 younger, nondyslexic readers were compared when they read aloud 2 texts. The study examined whether word-frequency and word-length effects previously found for skilled adult readers would generalize equally to younger dyslexic and nondyslexic readers. Significantly longer gaze durations and reinspection times were found for low-frequency and long words than for high-frequency and short words. The effects also showed up in the number of fixations on the target words. The effects did not differ significantly for the 2 experimental groups. The results run counter to the oculomotor dysfunction hypothesis of dyslexia. Instead, they support the view that both dyslexic and nondyslexic readers' eye fixation patterns reflect their difficulties in successfully identifying words in a text.

Computer-based phonological awareness and reading instruction.

Reading with Orthographic and Segmented Speech (ROSS) programs use talking computers to deal with deficits in word recognition and phonological awareness. With ROSS, children read stories on a computer screen. Whenever they encounter a word they find difficult, they can request assistance by targeting the word with a mouse. The program highlights the word in segments and then pronounces the segments in order. In previous studies, children improved in reading, but children with relatively lower initial phonological awareness (PA) gained less than the others. In order to maximize the benefits from ROSS for all children, the current study aimed to improve PA before and while reading with ROSS, by using some programs based on theAuditory Discrimination in Depth method (Lindamood and Lindamood 1975), and others focusing on phoneme manipulation with speech feedback for all responses. The study compared the effects of this training with training in Comprehension Strategies (CS) based on Reciprocal Teaching techniques (Palincsar and Brown 1984), among second- to fifth-grade students with problems in word recognition. While both groups received equal instructional time in small-groups and with the computer, the groups differed in how much time they spent reading words in context. Whereas PA children spent half their computer time on PA exercises involving individual words and half reading words in context with ROSS, the CS group spent all their computer time reading words in context with ROSS. Both groups made significant gains in decoding, word recognition, and comprehension; however the PA groups gained significantly more than the CS group on all untimed tests of phoneme awareness, word recognition, and nonsense word reading. The CS children performed better on a test of time-limited word recognition; they also achieved higher comprehension scores, although only while reading with a trainer. The PA children's improved decoding skill led to greater accuracy, but slower responses with difficult words, after one semester's training.

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.

Differential genetic etiology of reading disability as a function of IQ.

To test the hypothesis that the genetic etiology of reading disability differs as a function of IQ, composite reading performance data from 223 pairs of identical twins and 169 pairs of same-gender fraternal twins in which at least one member of each pair was classified with reading disability were subjected to multiple regression analysis (DeFries & Fulker, 1985, 1988). In the total sample, heritability of the group deficit in reading performance (h(g)2) was .58 (+/- .08). However, when the basic regression model was fitted separately to data from twin pairs with average Wechsler (1974, 1981) full scale IQ scores below 100 or 100 and above, resulting estimates of h(g)2 were .43 and .72, respectively, a significant difference (p < or = .03, one-tailed). The results of fitting extended regression models to reading performance and continuous IQ data provide evidence that the genetic etiology of reading disability differs as a linear function of IQ (p < or = .007, one-tailed). These results suggest that IQ is relevant for the diagnosis of reading disability and that environmental influences may be more salient as a cause of reading difficulties in children with lower IQ scores.

Reading disability and chromosome 6p21.3: evaluation of MOG as a candidate gene.

Linkage analysis has localized a gene influencing specific reading disability (dyslexia) to 6p21.3. The myelin oligodendrocyte glycoprotein (MOG) gene, which maps to this region, was selected as a candidate. Myelin oligodendrocyte glycoprotein is a membrane protein, a member of the immunoglobin superfamily, that is found on the outermost lamellae of mature myelin. Although the exact function of this protein is unknown, its presence in the central nervous system and the hypothesized relationship between dyslexia and temporal processing rate as well as a suggested relationship with intelligence made this gene a candidate for dyslexia. Analysis of the coding exons and adjacent splice sites in a subset of 22 children with dyslexia from 10 sibships found a missense mutation in exon 4 in 2 of the sibships. This change from the published sequence also occurred in 86 of 96 random controls, making it considerably less frequent in this small sample of individuals with dyslexia. Subsequent typing of this single nucleotide polymorphism (SNP) in 74 nuclear families in which at least one child had reading disability showed no significant difference in frequency from the controls, however. Sib-pair linkage analysis with these families did not show significant linkage with the SNP nor with a separate polymorphic dinucleotide repeat marker in the MOG gene (MOG31/32), but association analysis identified two alleles of MOG31/32 that were associated with reading disability phenotypes with a low level of significance. Thus, although alleles in the MOG gene may be in linkage disequilibrium with a locus that contributes to reading disability, it is unlikely that the MOG gene itself is involved.

The effects of an undergraduate clinical internship on the self-concept and professional role mastery of baccalaureate nursing students.

PURPOSE: The Purpose of this investigation was to determine whether an eight-week undergraduate clinical courses would enhance students' self-concepts and increase their perception of competence in critical care, teaching/collaboration, planning/evaluation, professional development, leadership and interpersonal skills, and communication. RESEARCH QUESTIONS: Is there a need for an undergraduate clinical internship? Will there be a difference in self-concept and perception of role mastery between the group of students who participated in the internship and those who did not participate? METHODOLOGY: Nursing students at the University who were between their junior and senior years were offered the opportunity to enroll in the course (didactic and clinical). Eight interns enrolled in the course; five non-interns enrolled in the didactic portion only; and the remaining 36 classmates were designated as the control group. DESIGN: A pretest-post test designed was utilized. Two instruments were used: 1) The Tennessee Self-Concept Scale and 2) The Six-Dimensional Scale of Nursing Performance. RESULTS: One way ANOVA with .05 level of significance was used as the statistical test. There were no significant differences noted.

Mentoring through predoctoral fellowships to enhance research productivity.

This article reports a study of the mentoring relationships that developed during predoctoral fellowships awarded to five nursing students who worked with faculty mentors at the University of Kansas, School of Nursing. Data were gathered through interviews and a written questionnaire from each of eight study participants (four of the five pairs). The analysis of interview and questionnaire data supported the existence of a mentoring relationship according to Yoder's (1990) model of mentoring, with the addition of two variables, socialization as a researcher and mutual sharing, that are unique to doctoral education. Themes that represented the experience of the mentor-protégé pairs were identified: (1) productivity, (2) work organization, (3) mutual learning, (4) problems encountered, (5) beneficial research application skills, and (6) innovative communication. All participants were enthusiastic about the experience, and students indicated increased confidence in application of the research process.

Genome-wide screening for DNA variants associated with reading and language traits.

Reading and language abilities are heritable traits that are likely to share some genetic influences with each other. To identify pleiotropic genetic variants affecting these traits, we first performed a genome-wide association scan (GWAS) meta-analysis using three richly characterized datasets comprising individuals with histories of reading or language problems, and their siblings. GWAS was performed in a total of 1862 participants using the first principal component computed from several quantitative measures of reading- and language-related abilities, both before and after adjustment for performance IQ. We identified novel suggestive associations at the SNPs rs59197085 and rs5995177 (uncorrected P ≈ 10(-7) for each SNP), located respectively at the CCDC136/FLNC and RBFOX2 genes. Each of these SNPs then showed evidence for effects across multiple reading and language traits in univariate association testing against the individual traits. FLNC encodes a structural protein involved in cytoskeleton remodelling, while RBFOX2 is an important regulator of alternative splicing in neurons. The CCDC136/FLNC locus showed association with a comparable reading/language measure in an independent sample of 6434 participants from the general population, although involving distinct alleles of the associated SNP. Our datasets will form an important part of on-going international efforts to identify genes contributing to reading and language skills.