Author Response to Comments

We thank Drs Buckley, Atanasova, Saenz, Rosembaum, and Spinazzi for their comments and value their perspectives and experience.Our motivation was to help pediatricians with clinical decision-making, in particular, with developmental screening and connecting children with services and supports. Most pediatricians see only a few children with Down syndrome, yet they are responsible for evaluating development, screening for autism spectrum disorder, and facilitating appropriate referrals.1 Without population-based descriptions of development, these clinicians may rely on gestalt, outdated views, or limited experience.A key message from our study2 is that there is great variability in the ages at which certain skills are observed, and we believe this message is consistent with the principle that every child’s journey is unique. Rather than normalizing delays, our efforts aim to provide more context for pediatricians that may help them prioritize competing concerns and develop tailored recommendations for children in their care. We agree that development is related to many factors and that better understanding of the social, educational, environmental, and medical influences on development is needed.We also agree that the data in our report do not represent the experiences of all individuals with Down syndrome. Our clinic-based population may display more medical complexity and have more individuals with greater developmental delays than what is seen elsewhere. Conversely, community-based studies, especially those that involve educational interventions, may underrepresent the neurodevelopmental complexity experienced by some individuals with Down syndrome. Work by Maatta et al indicates that up to 30% of children with Down syndrome demonstrate severe or profound levels of intellectual disability, and rates are higher among adults.3,4 This group of individuals might not readily volunteer for research studies, or they might be excluded because of hearing loss, vision issues, illness, or inability to complete standardized assessments. For example, the enrollment criteria in the studies by Galeote et al included “absence of neurosensory deficits and psychopathological disorders.”5,6 Future studies should aggregate observations from many populations to present a more complete understanding of the experiences of all individuals with Down syndrome.There may be other factors that account for differences between our study findings and those of others. Our study used caregiver report to characterize developmental skills (eg, vocabulary size or use of 2-word phrases), whereas other studies used standardized assessments conducted by trained staff. Caregiver report is subject to variation in interpretation of certain questions, and we acknowledge this limitation. However, caregiver report also provides insight into how acquired skills are being used, and this may be important information for providers.Finally, in practice, there are statistical methods available for analyzing longitudinal developmental data. We extended the logistic regression model previously used for the Denver Developmental Screening Test (Denver II)7 and applied logistic random-effects models to analyze our data, accounting for repeated measures. Motivated by the comments we have received here and elsewhere, we plan to also examine our data using alternative methods, such as those in a recently published study of developmental milestones.8 As with the Denver II, which was itself a revision prompted by concerns about the instrument and applicability to wider populations, our work will improve with feedback and collaboration.We hope efforts like ours will help pediatricians and families identify the needs for each individual child at a given time—not to impose rigid expectations, but instead to identify opportunities for intervention. We believe it is possible to work toward this goal while also believing that each child has the capacity to learn, grow, and achieve in their own way.