Diagnostic stability in young children at risk for autism spectrum disorder: a baby siblings research consortium study

BackgroundThe diagnosis of autism spectrum disorder (ASD) made before age 3 has been found to be remarkably stable in clinic- and community-ascertained samples. The stability of an ASD diagnosis in prospectively ascertained samples of infants at risk for ASD due to familial factors has not yet been studied, however. The American Academy of Pediatrics recommends intensive surveillance and screening for this high-risk group, which may afford earlier identification. Therefore, it is critical to understand the stability of an ASD diagnosis made before age 3 in young children at familial risk. MethodsData were pooled across seven sites of the Baby Siblings Research Consortium. Evaluations of 418 later-born siblings of children with ASD were conducted at 18, 24, and 36months of age and a clinical diagnosis of ASD or Not ASD was made at each age. ResultsThe stability of an ASD diagnosis at 18months was 93% and at 24months was 82%. There were relatively few children diagnosed with ASD at 18 or 24months whose diagnosis was not confirmed at 36months. There were, however, many children with ASD outcomes at 36months who had not yet been diagnosed at 18months (63%) or 24months (41%). ConclusionsThe stability of an ASD diagnosis in this familial-risk sample was high at both 18 and 24months of age and comparable with previous data from clinic- and community-ascertained samples. However, almost half of the children with ASD outcomes were not identified as being on the spectrum at 24months and did not receive an ASD diagnosis until 36months. Thus, longitudinal follow-up is critical for children with early signs of social-communication difficulties, even if they do not meet diagnostic criteria at initial assessment. A public health implication of these data is that screening for ASD may need to be repeated multiple times in the first years of life. These data also suggest that there is a period of early development in which ASD features unfold and emerge but have not yet reached levels supportive of a diagnosis.