The Cleveland Family Speech and Reading Study: A Review of Long-Term Outcomes Linking Phenotypes and Genotypes for Speech Sound Disorders.

PURPOSE: This article reviews findings from the Cleveland Family Speech and Reading Study, a 25-year longitudinal study of speech sound disorders (SSDs) of unknown etiology. The study sought to describe the long-term outcomes for individuals with early SSD, including those diagnosed with childhood apraxia of speech (CAS), and to identify genetic findings for endophenotypes and phenotypes associated with SSD.

METHOD: The data included in this article were collected from families (N = 296) with a child diagnosed with SSD. Probands and available siblings were assessed on a battery of speech, language, and literacy measures at preschool (4;0-6;11 [years;months]), school age (7;0-11;11), and adolescence/young adulthood (12-25 years). Families (N = 272) provided DNA samples, including 73 probands with CAS. Genome-wide association studies (N = 435) and whole genome sequencing (N = 101) analyses were conducted on a subset of the sample.

RESULTS

Poorer outcomes for adolescents/adults are associated with oral motor skills, an early history of motor difficulties, comorbid language impairment, and persistent speech sound errors. Children with SSD had both rare genetic and common variants that were correlative and may be causal. Several of these variants occurred de novo in the CAS proband with or without a family history of SSD, suggesting that de novo variants play a larger role in CAS and SSD than anticipated.

CONCLUSIONS

Some children with early SSD demonstrate persistent speech, language, and literacy difficulties in adolescence and adulthood, while others show partial or full resolution. Family health history questionnaires do not capture long-term outcomes; thus, finer long-term assessments are needed to identify phenotypes in older children. Genetic data suggest considerable locus heterogeneity. Having a compendium of variants for SSD, including CAS, will help practitioners move toward precision medicine with deep phenotyping supporting accurate diagnoses and personalized interventions.