Initial studies of the phenotype and persistence of speech motor delay (SMD).

Speech Motor Delay (SMD) is a recently proposed childhood motor speech disorder characterized by imprecise and unstable speech, prosody, and voice that does not meet criteria for either Childhood Dysarthria or Childhood Apraxia of Speech. The goals of the present research were to obtain information on the phenotype of SMD and initial information on the persistence of SMD in children receiving treatment for idiopathic Speech Delay (SD). Five questions about the phenotype and persistence of SMD were posed using a database of audio-recordings and participant records and longitudinal data from audio-recordings of children with early SMD treated for SD. Three phenotype questions examined associations between participant risk factors and prevalence of SMD, and described the most frequent speech, prosody, and voice signs of early SMD. To provide initial estimates of the persistence of SMD, two questions examined associations between the persistence of SMD and participant risk factors using the audio-recordings of 14 participants with SMD treated for idiopathic SD. Phenotype findings indicated that SMD is characterized by across-the-board delays in the spatiotemporal precision and stability of speech, prosody, and voice production. Persistence findings indicated that although most participants normalized early SMD by 6 years of age, SMD persisted until at least late adolescence in 21.4% of participants. Findings are interpreted to support the construct validity of SMD and the potential for research using additional assessment modalities to explicate its genomic and neuromotor causal pathways. Abbreviations: CAS: Childhood Apraxia of Speech; CD: Childhood Dysarthria; MSD: Motor Speech Disorder; No MSD: No Motor Speech Disorder; PSI: Precision-Stability Index; SD: Speech Delay; SMD: Speech Motor Delay; SSD: Speech Sound Disorders.