Abstract
Despite earlier claims that language abilities are intact in individuals with Williams syndrome (WS), many studies have shown that language development is often delayed and atypical, that is, it develops in line with different cognitive abilities compared to typically developing populations. It is unclear, however, whether general cognitive development predicts language comprehension in WS. The current study is the first to examine the development of grammatical comprehension in a large group (N = 58) of individuals with WS aged 5 to 21 years old. Grammatical comprehension is key to a person's ability to understand what is being said and engage in successful social interaction. Using cross-sectional developmental trajectories, performance on the Test for the Reception of Grammar was shown to increase with chronological age and performance was predicted by vocabulary scores, but not non-verbal ability. In addition, there was no meaningful difference between items that contained spatial language and similar grammatical constructions that did not contain spatial language and performance on both types of expressions was similarly predicted by vocabulary scores. Overall, these results show that grammatical development in WS is delayed but not atypical in its relationship to vocabulary.