Abstract
Language development, a core pillar of social communication, has variable trajectories in autism that include a regression or loss of skills in roughly 20% of autistic individuals. Language regression is most frequently identified through parent report but can also be observed as a decrease in raw scores on a repeated language assessment (measure-defined). Later language outcomes after regression have been observed to be highly variable, but not lower than children without a language regression. The current study explores rates of parent-reported and measure-defined language regression in a large sample of infants at high familial likelihood of autism due to having an older autistic sibling. Among all participants at high familial likelihood for autism ( n =428), parent-reported regression was observed in 2.8% ( n =12) and was associated with 2.77 times higher odds of receiving an autism diagnosis. Measure-defined regression was observed in 8% ( n =36) and was associated with 1.21 times higher odds of autism diagnosis. These rates of regression are expectedly lower than estimates collected in autistic samples. Neither of these elevated odds was statistically significant and there was low concordance between these groups with only one participant present in both. Nearest-neighbor comparison samples of non-autistic infants at high and low likelihood for autism without language regression were selected to assess differences in language growth trajectories associated with regression. Infants with parent-reported language regression showed comparable language development to a matched high-likelihood sample while infants with measure-defined language regression showed slower overall language development than matched peers. Taken together, our results show that parent-report and direct measurement of regression capture unique aspects of child language development that may not be predictive of an autism diagnosis but may indicate delayed language growth in early toddlerhood. These language outcomes support previous findings of wide heterogeneity among those with regression and continued language growth after loss of skills. KEY POINTS: Language regression can be captured through parent-report or decrease in raw scores on repeated language assessment and is reported in approximately 20% of autistic toddlers.Most research on language regression uses retrospective report of regression in autistic children, but this study prospectively examines regression in toddlers at high familial likelihood for autism who do and do not receive later diagnoses.Parent-reported and measure-defined regression in this high-likelihood sample have low concordance indicating that these may be different events in language development.The presence of language regression was not associated with significantly higher odds of receiving an autism diagnosis.Children who exhibit language regression continue growing and developing language and those with parent-reported regression display comparable language skills to children without language regression at three years of age.