Abstract
Given the importance of early detection, it is critical to understand the non-linearity in manifestation of ASD before age 24 months, when ASD symptoms are beginning to consolidate, through the age of 36 months when stability of ASD diagnosis is reportedly high into school-age when increased demands may challenge previously successful compensatory processes and permit first ASD detection. We employed a prospective, longitudinal design focused on children with an older sibling with ASD (n = 210) who received diagnostic evaluations at mean ages of 15.4 months (Time 1), 36.6 months (Time 2), and 5.7 years (Time 3) to examine: (1) diagnostic stability, (2) developmental trajectories associated with different patterns of ASD vs. non-ASD classifications, and (3) predictors of classification group over time. Clinical best estimate (CBE) diagnosis of ASD or non-ASD was made at each time point. Linear mixed-effects models were implemented to examine differences in developmental trajectories of stable and dynamic diagnostic groups. Multinomial logistic regression analyses were used to examine predictors of the likelihood of belonging to each CBE diagnostic classification group. Results revealed that sensitivity and stability of an ASD diagnosis significantly increased from Time 1 (sensitivity: 52%; stability: 63%) to Time 2 (sensitivity: 86%; stability: 68%). Different developmental trajectories of autism symptom severity and non-verbal and verbal IQ were observed across groups, with differences first observed at Time 1 and becoming more pronounced through Time 3. Presence of restricted and repetitive behaviors as well as limitations in initiation of joint attention and expressive language skills differentially predicted the likelihood of belonging to the different CBE diagnostic classification groups. Results suggest that ASD symptoms may emerge or attenuate over time, with some children meeting diagnosis at follow-up, and other children no longer meeting diagnostic criteria. From a systems perspective, diagnostic non-linearity may be viewed as a dynamic developmental process, where emergent properties arising from various biological, genetic, and experiential factors interact, culminating in phenotypic phenomena that change over time. Clinical implications include extending universal ASD and social communication screening into school-age, supporting families' understanding of diagnostic shifts, and ensuring unbiased diagnostic decision-making when following children with ASD.
Highlights
Autism spectrum disorder (ASD) affects multiple developmental systems, presents along a continuum of severity [1, 2] and often, co-occurs with other conditions [3, 4]
To examine the stability at early school-age of ASD Clinical best estimate (CBE) diagnostic classifications made at the mean ages of 15 (Time 1) and 36-months (Time 2), we examined sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV)
We examined ASD diagnostic stability beginning at the end of the ASD prodromal period, with follow-up assessments at the age of three years, and at early school-age, when contextual demands on social and language processing increase substantially and could exceed children’s compensatory abilities, thereby permitting first ASD detection
Summary
Autism spectrum disorder (ASD) affects multiple developmental systems, presents along a continuum of severity (i.e., in social communication, language, and cognitive functioning, as well as in restricted and repetitive behaviors) [1, 2] and often, co-occurs with other conditions [3, 4]. Advantages of this approach include sample ascertainment independently of a clinical diagnosis or screening status (at time of recruitment), careful phenotypic assessment by experts in very early ASD diagnosis, use of state-of-the-science diagnostic procedures at established ages, and the ability to follow children who demonstrate a continuum of developmental functioning and range of diagnostic classifications (e.g., neurotypical, language disorder, ASD) This approach affords the ability to examine dynamic developmental processes, elucidate stability of ASD diagnosis and its relation to age of diagnosis, identify trajectories of dimensional characteristics of development, and identify predictors of different ASD positive/negative classifications over time. Early expressive language and frequency of initiation of joint attention are predictive of pragmatic communication skills (a core feature of ASD) at adolescence [33, 39, 41]
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