Infant muscle tone and childhood autistic traits: A longitudinal study in the general population

In a longitudinal population-based study of 2,905 children, we investigated if infants' neuromotor development was associated with autistic traits in childhood. Overall motor development and muscle tone were examined by trained research assistants with an adapted version of Touwen's Neurodevelopmental Examination between ages 2 and 5 months. Tone was assessed in several positions and items were scored as normal, low, or high tone. Parents rated their children's autistic traits with the Social Responsiveness Scale (SRS) and the Pervasive Developmental Problems (PDP) subscale of the Child Behavior Checklist at 6 years. We defined clinical PDP if scores were >98th percentile of the norm population. Diagnosis of autism spectrum disorder (ASD) was clinically confirmed in 30 children. We observed a modest association between overall neuromotor development in infants and autistic traits. Low muscle tone in infancy predicted autistic traits measured by SRS (adjusted beta = 0.05, 95% CI for B: 0.00-0.02, P = 0.01), and PDP (adjusted beta = 0.08, 95% CI for B: 0.04-0.10, P