Amy J. Hansen

Pleiotropic Effects of a Chromosome 3 Locus on Speech-Sound Disorder and Reading

Speech-sound disorder (SSD) is a complex behavioral disorder characterized by speech-sound production errors associated with deficits in articulation, phonological processes, and cognitive linguistic processes. SSD is prevalent in childhood and is comorbid with disorders of language, spelling, and reading disability, or dyslexia. Previous research suggests that developmental problems in domains associated with speech and language acquisition place a child at risk for dyslexia. Recent genetic studies have identified several candidate regions for dyslexia, including one on chromosome 3 segregating in a large Finnish pedigree. To explore common genetic influences on SSD and reading, we examined linkage for several quantitative traits to markers in the pericentrometric region of chromosome 3 in 77 families ascertained through a child with SSD. The quantitative scores measured several processes underlying speech-sound production, including phonological memory, phonological representation, articulation, receptive and expressive vocabulary, and reading decoding and comprehension skills. Model-free linkage analysis was followed by identification of sib pairs with linkage and construction of core shared haplotypes. In our multipoint analyses, measures of phonological memory demonstrated the strongest linkage (marker D3S2465, P=5.6 x 10(-5), and marker D3S3716, P=6.8 x 10(-4)). Tests for single-word decoding also demonstrated linkage (real word reading: marker D3S2465, P=.004; nonsense word reading: marker D3S1595, P=.005). The minimum shared haplotype in sib pairs with similar trait values spans 4.9 cM and is bounded by markers D3S3049 and D3S3045. Our results suggest that domains common to SSD and dyslexia are pleiotropically influenced by a putative quantitative trait locus on chromosome 3.

Relationship Between Speech-Sound Disorders and Early Literacy Skills in Preschool-Age Children: Impact of Comorbid Language Impairment

Objective: Disorders of articulation or speech-sound disorders (SSD) are common in early childhood. Children with these disorders may be at risk for reading difficulties because they may have poor auditory, phonologic, and verbal memory skills. Methods: We sought to characterize the reading and writing readiness of preschool children with SSD and identify factors associated with preliteracy skills. Subjects were 125 children aged 3 to 6 years with moderate to severe SSD; 53% had comorbid language impairment (LI). Reading readiness was measured with the Test of Early Reading Ability-2 (TERA) and writing skills with the Test of Early Written Language-2 (TEWL), which assessed print concept knowledge. Linear regression was used to examine the association between SSD severity and TERA and TEWL scores and analysis of variance to examine the effect of comorbid LI. Performance on a battery of speech and language tests was reduced by way of factor analysis to composites for articulation, narrative, grammar, and word knowledge skills. Results: Early reading and writing scores were significantly lower for children with comorbid LI but were not related to SSD severity once language status was taken into account. Composites for grammar and word knowledge were related to performance on the TERA and TEWL, even after adjusting for Performance IQ. Below average language skills in preschool place a child at risk for deficits in preliteracy skills, which may have implications for the later development of reading disability. Conclusion: Preschool children with SSD and LI may benefit from instruction in preliteracy skills in addition to language therapy.

Heritability Estimation for Speech-Sound Traits with Developmental Trajectories

Numerous studies have examined genetic influences on developmental problems such as speech sound disorders (SSD), language impairment (LI), and reading disability. Disorders such as SSD are often analyzed using their component endophenotypes. Most studies, however, have involved comparisons of twin pairs or siblings of similar age, or have adjusted for age ignoring effects that are peculiar to age-related trajectories for phenotypic change. Such developmental changes in these skills have limited the usefulness of data from parents or siblings who differ substantially in age from the probands. Employing parent–offspring correlation in heritability estimation permits a more precise estimate of the additive component of genetic variance, but different generations have to be measured for the same trait. We report on a smoothing procedure which fits a series of lines that approximate a curve matching the developmental trajectory. This procedure adjusts for changes in measures with age, so that the adjusted values are on a similar scale for children, adolescents, and adults. We apply this method to four measures of phonological memory and articulation in order to estimate their heritability. Repetition of multisyllabic real words (MSW) showed the best heritability estimate of 45% in this sample. We conclude that differences in measurement scales across the age span can be reconciled through non-linear modeling of the developmental process.