Language comprehension developmental milestones in typically developing children assessed by the new Language Phenotype Assessment (LPA)

We recently identified three distinct phenotypes of language comprehension in 31,000 autistic individuals ¹ : 1) individuals with the Command Phenotype were limited to comprehension of simple commands; 2) individuals with the Modifier Phenotype demonstrated additional comprehension of color, size, and number modifiers; and 3) individuals with the Syntactic Phenotype added comprehension of spatial prepositions, verb tenses, flexible syntax, possessive pronouns, complex explanations, and fairytales. We hypothesized that typically developing children progress through the same three language comprehension phenotypes and aimed to investigate the typical age at which each phenotype emerged. To evaluate comprehension in young children, we developed a new assessment, the 15-item Language Phenotype Assessment (LPA), which utilizes toy-animal manipulatives to avoid reliance on picture interpretation and includes short instructions to reduce auditory memory load. The LPA was administered to 116 typically-developing children aged 1.5 to 7 years. Results revealed a developmental pattern in line with the three previously described phenotypes: 50% of typically developing children attained the Command Phenotype by 1.5-years, the Modifier Phenotype by 3.0-years, and the Syntactic Phenotype by 3.7-years-of-age. Future research should focus on establishing normative data for the LPA to enable earlier identification of language comprehension challenges, facilitating timely initiation of language interventions.