Genetics of specific reading disability

Genetic influences on early word recognition abilities and disabilities: a study of 7‐year‐old twins

“…Shared environmental factors, in contrast, accounted for 21–50% of group deficits. These findings corroborate, with a younger and larger sample, similar results from the CLDRC study (DeFries & Alarcón, 1996; Gayán & Olson, 2001). The convergence of findings indicates that the group deficits in word recognition in the early school years are at least as heritable as group deficits in later childhood and adolescence.…”

A meta-analytic review of cognition and reading difficulties: Individual differences, moderation, and language mediation mechanisms.

“…After controlling for moderators and covariates, we found that the RD comorbid groups, in comparison with RD only, showed more severe deficits only on working memory. Thus, our findings generally align with the multiple deficits hypothesis: RD only and comorbid RD may share similar cognitive deficit profiles, attributable perhaps to common etiological influences that increase susceptibility to each individual disorder (DeFries & Alarcón, 1996; Faraone et al, 2001; Plomin & Kovas, 2005). That said, in the present study, the limited number of effect sizes did not permit the systematic investigation of heterogeneity within the RD comorbid group, which includes comorbidity with mathematics difficulties, autism, language problems, writing problems, behavioral problems, ADHD, and the like.…”

The etiological relationship between reading disability and phonological disorder

“…In the case of DZ twins, out of 311 cases where a proband with RD was selected, there were 174 cases (55.9%) where the cotwin also had RD. These concordance rates were significantly different (X2(1) = 95.84, p<.001), supporting the heritability of RD and consistent with other results from this sample (e.g., DeFries & Alarc6n, 1996).…”