Familial dyslexia: genetic and medical findings in eleven three-generation families

Abstract

In addition to providing information on the inheritance of dyslexia, the present study of eleven three-generation families has provided a unique opportunity to compare affected and unaffected family members at all ages. The data presented here are based on pedigree information, a questionnaire administered to all participating family members in relation to sex ratio, handedness, the severity of dyslexia by sex, pre- and perinatal complications, medical complications, years of education and earning ability, and a battery of standardized tests to define the presence or absence of dyslexia. The pattern of inheritance was consistent with the postulated autosomal dominant mode of inheritance and penetrance was found to be > 90 percent. Of 73 individuals determined to have a gene leading to dyslexia, seven were classified as obligate carriers and six as compensated adults who had no current symptoms or diagnostic evidence of dyslexia. The sex ratio (1.06) was not different from the expected ratio of 1.04. Left-handedness, major pre- and perinatal complications, and autoimmune disorders and allergy were not more common in dyslexics than non-dyslexics. The number of years of education and average income were similar in affected and unaffected family members. Compensated adults and obligate carriers were similar to unaffected family members in each of these parameters.

Gender ratio in dyslexia

“…More recently, however, this imbalance has been called into question (Shaywitz et al 1990;Wadsworth et al 1992;Lubs et al 1993).…”

“…These included 223 boys and 46 girls, for a ratio of 4.51 to 1. Two possible difficulties in interpreting these data are discussed, and a defense is offered of the criteria used.Since some recent research papers report a gender ratio much nearer 1:1 (Shaywitz et al 1990;Wadsworth et al 1992;Lubs et al 1993), those papers were examined for possible differences in procedure; it was found that the definition of dyslexia they used was "poor reading in relation to intelligence." We carried out a further analysis on our own data using the same criterion.…”

A genome-wide search strategy for identifying quantitative trait loci involved in reading and spelling disability (developmental dyslexia)

“…This breakdown of simple phenotype-genotype correspondence is due to a number of factors. Segregation analyses of reading disability (17,18,20) suggest that the disorder is genetically heterogeneous, meaning that different genes may influence the trait in different families. In addition, there may be reduced penetrance, where some individuals who inherit a predisposing allele do not develop the disorder, and/or phenocopy, where individuals who do not inherit a predisposing allele do manifest the trait (as a consequence of environmental or random factors).…”

Familial Dyslexia in a Large Swedish Family: A Whole Genome Linkage Scan

“…The primary problem in dyslexia is a weakness in the rapid, fluent and accurate decoding of written words caused by a shortcoming in the phonological system (Høien and Lundberg 2001;Ramus and Szenkovits 2008;Stanovich and Siegel 1994). An abundance of research has demonstrated that it is highly inheritable (Barr and Couto 2007;DeFries and Gillis 1993;Gayán and Olson 2003;Hallgren 1950Hallgren , 2003Lubs et al 1993;Fisher and Smith 2001;Grigorenko 2005;Smith 2007). Grigorenko (2001) reviewed eight family studies, including in all 516 families, and found a median value of 37% of reading problems in parents of children with reading difficulties.…”