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ObjectivesAutism spectrum disorder (ASD) is estimated to be ∼10 times higher in children with versus without an autistic sibling in population-based studies. Prospective studies of infant siblings have revealed even higher familial recurrence rates. In the current prospective longitudinal study, we provide updated estimates of familial ASD recurrence using a multinational database of infants with older autistic siblings.MethodsData were collated across 18 sites of the Baby Siblings Research Consortium, an international network studying the earliest manifestations of ASD. A total of 1605 infants with an older autistic sibling were followed from early in life to 3 years, when they were classified as ASD or non-ASD. Hierarchical generalized linear modeling, with site as a random effect, was used to examine predictors of recurrence in families and calculate likelihood ratios.ResultsA total of 20.2% of siblings developed ASD, which is not significantly higher than the previously reported rate of 18.7%. Male infant sex and >1 older affected sibling were significant predictors of familial recurrence. Proband sex also influenced recurrence rates, with siblings of female probands significantly more likely to develop ASD than siblings of male probands. Race and maternal education were also associated with recurrence in families.ConclusionsThe familial recurrence rate of ASD, as measured in infant sibling studies, has not changed appreciably since previous estimates were made in 2011. Younger siblings of autistic children, particularly those who are male, have an affected female sibling, multiple affected siblings, or are impacted by social inequities, should be closely monitored and promptly referred for diagnostic evaluation.

This study examined the construct validity of the Autism Classification System of Functioning: Social Communication (ACSF). Participants included 145 parents of children with autism (2-19 years). The degree of convergent and discriminant validity between parent reported ACSF and subscales from Social Responsiveness Scale 2nd edition and Behavior Assessment System for Children, 3rd Edition were examined against a priori hypotheses. We examined construct validity in the entire sample as well as in specific age cohorts. Our findings suggest that ACSF can provide a valid classification system of social communication ability in children with autism 2-19 years of age, and its two subscales may be used to examine different aspects of social communication ability.

The Autism Voices study draws on novel inclusive methods to obtain the first-person experiences of autistic youth with a range of cognitive and verbal abilities. Thirty-one autistic youth were interviewed with a strength-based protocol, enabling them to provide responses in the modality of their choice. Dynamics between youth and their environments such as home, school, and community were explored. Youth were questioned about their interests, plans for the future, experiences with various emotions, and experience of autism. Based on a thematic analysis, six themes emerged: (1) autistic identities, (2) thinking about the future, (3) seeking social connection on their own terms, (4) seeking autonomy, (5) school as both a stressor and social facilitator, and (6) experiences of stress and anxiety. The experiences described by autistic youth parallel many of the aspirations and challenges of typically developing adolescents, while being uniquely shaped by their autism. We discuss how these insights shared by autistic youth can facilitate active involvement in their communities, promote well-being, and promote optimal transition into adulthood. Autism Voices demonstrates that partnering with multiple stakeholders and the use of inclusive methodologies are pivotal steps toward capturing the voices of all autistic youth.

Fully understanding autism spectrum disorder (ASD) genetics requires whole-genome sequencing (WGS). We present the latest release of the Autism Speaks MSSNG resource, which includes WGS data from 5,100 individuals with ASD and 6,212 non-ASD parents and siblings (total n = 11,312). Examining a wide variety of genetic variants in MSSNG and the Simons Simplex Collection (SSC; n = 9,205), we identified ASD-associated rare variants in 718/5,100 individuals with ASD from MSSNG (14.1%) and 350/2,419 from SSC (14.5%). Considering genomic architecture, 52% were nuclear sequence-level variants, 46% were nuclear structural variants (including copy-number variants, inversions, large insertions, uniparental isodisomies, and tandem repeat expansions), and 2% were mitochondrial variants. Our study provides a guidebook for exploring genotype-phenotype correlations in families who carry ASD-associated rare variants and serves as an entry point to the expanded studies required to dissect the etiology in the ∼85% of the ASD population that remain idiopathic.

Research regarding autistic children's sibling relationship quality is mixed, although some literature suggests poorer quality compared to children with other disabilities or who are neurotypical. Little is known about how the clinical characteristics of autistic children relate to parent perceptions of sibling relationship quality. We drew data from a subsample of 119 children on the autism spectrum, ages 10-11 years, from an ongoing longitudinal study. Hierarchical multiple regressions tested the extent to which children's autism symptoms, behavioral difficulties, and communication abilities related to four domains of parent-rated sibling relationship quality. We also examined communication ability as a moderator of the effect of behavioral difficulties on parent-rated sibling relationship quality. More severe autism symptoms were associated with lower levels of conflict and rivalry, whereas higher communication ability was related to more relative status/power, but also conflict. Communication ability moderated the effect of behavioral difficulties such that behavioral difficulties were more closely associated with less warmth/closeness when children had weaker communication skills; behavioral difficulties were not significantly associated with other domains of sibling relationship quality. Findings underscore the importance of considering clinical characteristics and multiple domains of relationship quality to better understand how parents view the relationships between autistic children and their siblings.

We examined the narrative abilities of bilingual and monolingual children on the autism spectrum (AS), whether bilinguals presented stronger social and pragmatic language abilities compared to monolinguals, and the link between narrative, social, and pragmatic language abilities. The narrative, social, and pragmatic language skills of school-aged bilinguals (n = 54) and monolinguals (n = 80) on the AS were assessed using normed measures. Language exposure was estimated through a parent questionnaire. Bilinguals performed similarly to monolinguals on measures of narrative, social, and pragmatic language skills. However, balanced bilinguals performed better on a nonliteral language task. Overall, results indicate that bilingual children on the AS can become as proficient in using language as monolinguals and may enjoy a bilingual advantage.

We examined the relationship between weight status, appetite regulating hormones, and mealtime behaviors among children, (5-12 years old), diagnosed with Autism Spectrum Disorder (ASD) in a cross-sectional study. All (N = 21) completed anthropometry measurements and (n = 18) provided blood samples for hormone analysis. Mealtime behavior, dietary, physical activity, puberty stage, and social impairment data were collected. Under fasting conditions, overweight/obese (OWOB) participants, (n = 6), had higher leptin concentrations (p < 0.02) and more feeding challenges (p < 0.05) than normal weight (n = 15). Higher leptin levels and disruptions in mealtime behaviors may exist among OWOB children in this study. Future longitudinal studies that examine appetite regulating hormones and mealtime behaviors may inform our understanding of the role of these markers in the development of obesity in ASD.

Participation in daily activities is often linked to functional independence and well-being, yet individual variability in participation and factors associated with that variation have rarely been examined among autistic youth. We applied latent profile analysis to identify subgroups of youth based on parent-reported activity participation frequency at home, school and community, as well as associations with youth characteristics, family demographics and environmental supportiveness among 158 autistic youth (aged 11-14 years at baseline). Three-, three- and two-profile solutions were selected for home, school and community settings, respectively; the most prevalent profiles were characterized by frequent home participation (73%), low participation in non-classroom activities at school (65%) and low community participation, particularly in social gatherings (80%), indicating participation imbalance across settings. More active participation profiles were generally associated with greater environmental support, higher cognitive and adaptive functioning and less externalizing behaviour. Latent transition analysis revealed overall 75% stability in profile membership over approximately 1 year, with a different home participation profile emerging at the second time-point. Our findings highlighted the variable participation patterns among autistic youth as associated with individual, family and environmental factors, thus stressing the need for optimizing person-environment fit through tailored supports to promote autistic youth's participation across settings.

This study examined the construct validity of the Autism Classification System of Functioning: Social Communication (ACSF). Participants included 145 parents of children with autism (2-19 years). The degree of convergent and discriminant validity between parent reported ACSF and subscales from Social Responsiveness Scale 2nd edition and Behavior Assessment System for Children, 3rd Edition were examined against a priori hypotheses. We examined construct validity in the entire sample as well as in specific age cohorts. Our findings suggest that ACSF can provide a valid classification system of social communication ability in children with autism 2-19 years of age, and its two subscales may be used to examine different aspects of social communication ability., Author(s): Diana Tajik-Parvinchi [sup.1] [sup.9] , Peter Rosenbaum [sup.2] , Mary Jo Cooley Hidecker [sup.3] , Eric Duku [sup.4] , Lonnie Zwaigenbaum [sup.5] , Caroline Roncadin [sup.6] , Stelios Georgiades [...]

The Autism Classification System of Functioning: Social Communication (ACSF) describes social communication functioning levels. First developed for preschoolers with ASD, this study tests an expanded age range (2-to-18 years). The ACFS rates the child's typical and best (i.e., capacity) performance. Qualitative methods tested parent and clinician perspectives of the ACSF age expansion using content analysis. The ACSF was used twice by parents and professionals for the same child/youth. Reliabilities were assessed using weighted kappa. Content validity supported the ACSF's applicability, clarity, and usability. The ACSF adaptations did not change its original construct. Reliability were calculated from 90 parent and professional Time-1 and Time-2 ratings for children/youth (2.1-15.6 years). Results showed good-to-very good intra-rater agreement (typical) and good inter-rater agreement (capacity).

Evidence supports early intervention for toddlers with ASD, but barriers to access remain, including system costs, workforce constraints, and a range of family socio-demographic factors. An urgent need exists for innovative models that maximize resource efficiency and promote widespread timely access. We examined uptake and outcomes from 82 families participating in a parent-mediated intervention comprising group-based learning and individual coaching, delivered either in-person (n = 45) or virtually (n = 37). Parents from diverse linguistic, ethnic, and educational backgrounds gained intervention skills and toddlers evidenced significant social-communication gains. Few differences emerged across socio-demographic factors or delivery conditions. Findings highlight the feasibility, acceptability, and promise of group-based learning when combined with individual coaching, with added potential to increase program reach via virtual delivery.

Recent efforts have focused on developing and evaluating early intervention for toddlers with probable or emerging autism spectrum disorder. Parent-mediated approaches have gained traction, with mounting evidence of efficacy, but a research-to-practice gap exists, and community effectiveness remains to be firmly established. We report outcomes of a parent-mediated toddler intervention delivered through a research-community partnership, using a community-partnered participatory framework. Data were available for 179 of 183 toddler-parent dyads receiving Social ABCs parent coaching (mean toddler age: 25.18 months; range, 14-34 months). Of these, 89.4% completed the 12-week program and 70.6% returned for 3-month follow-up assessment. Parents attained implementation fidelity exceeding 75%, and toddlers made gains on proximal and distal measures of social communication. Parent fidelity was associated with toddlers' responsivity at week 12, and responsivity predicted later language gains and reduced autism spectrum disorder symptoms. The roles of child, family, and system factors are discussed. Community delivery of an evidence-based parent-mediated intervention for toddlers with autism spectrum disorder is feasible and effective. Given resource efficiencies associated with parent-mediated approaches, findings bolster current efforts to promote earlier and more widespread access to intervention at the first signs of developmental concern.

Mental health problems are prevalent in autistic youth, but the underpinning mechanisms are not well explored. In neurotypical youth, stressful life events are an established risk factor for mental health problems. This study tested longitudinal bidirectional associations between family-level stressful life events and mental health problems and whether these were moderated by cognitive flexibility, in a cohort of autistic children (N = 247). Family-stressful life events, assessed using the parent-reported Family Inventory of Life Events and Changes, and mental health problems, assessed using the teacher-reported Child Behavior Checklist Internalizing and Externalizing Symptoms subscales, were measured at multiple points between 7 and 11 years. Analyses showed no significant pathways from internalizing or externalizing symptoms to family-stressful life events or from family-stressful life events to internalizing or externalizing symptoms. There was some evidence of moderation by cognitive flexibility; the family-stressful life events to internalizing symptoms pathway was non-significant in the group with typical shifting ability but significant in the group with clinically significant shifting problems. Information about family-level stressful life event exposure and cognitive flexibility may be helpful in identifying autistic youth who may be at higher risk of developing mental health problems. Established risk factors for mental health problems in neurotypical populations are relevant for understanding mental health in autistic youth. [This article was written with the Pathways in ASD Study Team.]

Research concerning temperament in children and adults with autism spectrum disorder (ASD) has suggested a consistent profile of low positive affect, high negative affect, and low regulation (Visser et al., 2016). One area receiving less attention is individual differences among children diagnosed with ASD. The primary objective of this study was to use a person-centered approach to explore heterogeneity of early temperament precursors of regulation in a large sample of infants with elevated familial likelihood of ASD. Early precursors of regulation included temperament assessed at 6, 12, and 24 months whereas outcome measures were diagnosis of ASD, cognitive ability and adaptive behavior at 36 months. Participants included 176 low-likelihood and 473 elevated-likelihood infants, 129 of whom were diagnosed with ASD at 3 years. Results supported a three-profile solution: a well-regulated profile (high positive affect and high attentional focus and shifting), a low attention focus profile (higher attentional shifting compared to attentional focus), and a low attention shifting profile (higher attentional focus compared to attentional shifting). A higher proportion of children diagnosed with ASD were classified into the low attention shifting profile. Furthermore, children with the well-regulated profile were differentiated from the other profiles by a pattern of higher social competence and lower dysregulation whereas children with the low attention focus profile were distinguished from the other profiles by higher cognitive ability at 3 years. The findings indicate that the combination of early positive affect with attention measures may provide an enhanced tool for prediction of self-regulation and later outcomes.

Opportunities to communicate first-person perspectives are essential for self-determination. However, many autistic youth are excluded from sharing their perspectives, specifically those who are minimally verbal or with lower intellectual functioning. Current challenges to capturing their voices include a lack of appropriate inclusive methodologies. Propose an inclusive strength-oriented method to capture first-person perspectives of autistic adolescents. Our protocol ("Autism Voices") includes a pre-interview survey and semi-structured interview using universal design strategies. It was piloted with 33 participants who were representative of diverse language and cognitive abilities. A coding scheme was developed to identify communicative acts used by participants and mitigation strategies used by interviewers to enhance communication. Interviewer strategies that enhanced communication included question formulation, use of pictures, offering various output modalities, and flexible implementation of the protocol. Non-verbal and alternative communication responses (e.g. choosing to not respond) were informative to youth's lived experience, especially for minimally verbal participants. Overall, our results highlight that communication goes beyond verbally answering questions and that participants' unconventional communication conveyed rich information. Autism Voices provides a promising method to promote the inclusion of autistic youth in research.

Autism spectrum disorder (ASD) impacts an individual's ability to socialize, communicate, and interact with, and adapt to, the environment. Over the last two decades, research has focused on early identification of ASD with significant progress being made in understanding the early behavioral and biological markers that precede a diagnosis, providing a catalyst for pre-symptomatic identification and intervention. Evidence from preclinical trials suggest that intervention prior to the onset of ASD symptoms may yield more improved developmental outcomes, and clinical studies suggest that the earlier intervention is administered, the better the outcomes. This article brings together a multidisciplinary group of experts to develop a conceptual framework for behavioral intervention, during the pre-symptomatic period prior to the consolidation of symptoms into diagnosis, in infants at very-high-likelihood for developing ASD (VHL-ASD). The overarching goals of this paper are to promote the development of new intervention approaches, empirical research, and policy efforts aimed at VHL-ASD infants during the pre-symptomatic period (i.e., prior to the consolidation of the defining features of ASD).

The COVID-19 pandemic has posed unique challenges for families and caregivers, as well as for autism-focused clinicians, who are faced with providing a thorough and accurate evaluation of children's specific needs and diagnoses in the absence of in-person assessment tools. The shift to telehealth assessments has challenged clinicians to reconsider approaches and assumptions that underlie the diagnostic assessment process, and to adopt new ways of individualizing standard assessments according to family and child needs. Mandates for physical distancing have uncovered deficiencies in diagnostic practices for suspected autism and have illuminated biases that have posed obstacles preventing children and families from receiving the services that they truly need. This Commentary outlines several considerations for improving diagnostic practices as we move forward from the current pandemic and continue to strive to build an adaptable, sustainable, equitable, and family-centered system of care. LAY SUMMARY: Physical distancing and the abrupt end to in-person services for many children on the autism spectrum has forced clinicians to examine the existing challenges with autism spectrum disorder (ASD) diagnostic assessment and consider things they want to keep and things that should be changed in the years ahead. New approaches such as telehealth both alleviated and exacerbated existing disparities, and brought into stark focus the importance of equitable and timely access to family-centered care. This commentary suggests ways of improving clinical practices related to ASD assessment to continue along this path.

We examined the relations of restricted and repetitive behaviors (RRB; insistence on sameness, repetitive sensory-motor, self-injurious behavior) to social skills overall and aspects that comprise social skills as measured by the VABS-II (coping skills, play/leisure time, interpersonal relationships) in 24- (n = 63) and 36-month old (n = 35), high-familial-risk toddlers with ASD. Hierarchical linear regression results indicated that repetitive sensory-motor was the best predictor of social skills overall. Secondary results indicated that all three RRB subtypes were associated with each subdomain of social skills; however, repetitive sensory-motor was the strongest and most consistent among these effects. While our results suggests a general negative relation of subtypes of RRB to aspects of adaptive social function, repetitive sensory-motor behaviors may be of particular relevance to the development of social skills during toddlerhood. [This article was written with the IBIS Network.]

Using the Infant Behavior Questionnaire--Revised in a longitudinal sample of infant siblings of autistic children (HR; n = 427, 171 female, 83.4% White) and a comparison group of low-risk controls (LR, n = 200, 86 female, 81.5% White), collected between 2007 and 2017, this study identified an invariant factor structure of temperament traits across groups at 6 and 12 months. Second, after partitioning the groups by familial risk and diagnostic outcome at 24 months, results reveal an endophenotypic pattern of Positive Emotionality at both 6 and 12 months, (HR-autism spectrum disorder [ASD] < HR-no-ASD < LR). Third, increased 'Duration of Orienting' at 12 months was associated with lower scores on the 24-month developmental outcomes in HR infants. These findings may augment efforts for early identification of ASD.

This study examined the trajectories of autistic symptom severity in an inception cohort of 187 children with ASD assessed across four time points from diagnosis to age 10. Trajectory groups were derived using multivariate cluster analysis. A two trajectory/cluster solution was selected. Change in trajectory slopes revealed a "turning point" marked by plateauing in symptom reduction during the period of transition to school (age 6) for one of the two trajectories. Trajectories were labelled: "Continuously Improving" (27%) and "Improving then Plateauing" (73% of sample). Children in the two trajectories differed in levels of symptom severity, language, cognitive, and adaptive functioning skills. Study findings can inform the development of more personalized services for children with ASD transitioning into the school system.

Infant vocalizations are early-emerging communicative markers shown to be atypical in autism spectrum disorder (ASD), but few longitudinal, prospective studies exist. In this study, 23,850 infant vocalizations from infants at low (LR)- and high (HR)-risk for ASD (HR-ASD = 23, female = 3; HR-Neg = 35, female = 13; LR = 32, female = 10; 80% White; collected from 2007 to 2017 near Philadelphia) were analyzed at 6, 12, and 24 months. At 12 months, HR-ASD infants produced fewer vocalizations than HR-Neg infants. From 6 to 24 months, HR-Neg infants demonstrated steeper vocalization growth compared to HR-ASD and LR infants. Finally, among HR infants, vocalizing at 12 months was associated with language, social phenotype, and diagnosis at age 2. Infant vocalizing is an objective behavioral marker that could facilitate earlier detection of ASD. [This article was co-authored with IBIS Network.]

The Autism Classification System of Functioning: Social Communication (ACSF) describes social communication functioning levels. First developed for preschoolers with ASD, this study tests an expanded age range (2-to-18 years). The ACFS rates the child's typical and best (i.e., capacity) performance. Qualitative methods tested parent and clinician perspectives of the ACSF age expansion using content analysis. The ACSF was used twice by parents and professionals for the same child/youth. Reliabilities were assessed using weighted kappa. Content validity supported the ACSF's applicability, clarity, and usability. The ACSF adaptations did not change its original construct. Reliability were calculated from 90 parent and professional Time-1 and Time-2 ratings for children/youth (2.1-15.6 years). Results showed good-to-very good intra-rater agreement (typical) and good inter-rater agreement (capacity)., Author(s): Briano Di Rezze [sup.1] , Stephen James Gentles [sup.2] , Mary Jo Cooley Hidecker [sup.3] , Lonnie Zwaigenbaum [sup.4] , Peter Rosenbaum [sup.5] , Eric Duku [sup.6] , Stelios [...]

This study examined parental perceptions of the character traits of children with autism from early childhood to age 11. Parents (n = 153) provided descriptions of the "best things" about their children on the Child Behavior Checklist (CBCL) at ages 3-4, 7-8, and 10-11 years. Descriptions were coded using the framework of the Values in Action Classification of Strengths, with additional traits added as needed. Parent-endorsed traits included love, kindness, happiness, and humor in children across all ages and traits such as perseverance as children entered school. Higher CBCL scores were associated with a lower likelihood of endorsement for Humanity traits. Results are congruent with a contemporary neurodiversity perspective that emphasizes strengths and resilience.

Families with early concerns about infant symptoms of ASD have limited access to experienced professionals for screening and guidance. Telehealth has been used to reduce access disparities in other pediatric populations and has shown promise in parent-implemented interventions for ASD. We investigated the feasibility of a novel level-2 telehealth assessment of infants' early social communication and ASD symptoms, the Telehealth Evaluation of Development for Infants (TEDI). Parents of eleven infants aged 6-12 months were coached to administer specific semi-structured behavioral probes. Initial feasibility, reliability, and acceptability benchmarks were met. These findings suggest the feasibility of screening infants via telehealth, and are supportive of further large-scale efforts to validate this method for longitudinal monitoring of symptomatic infants in community settings.

Despite considerable progress in characterizing the early signs of autism spectrum disorder (ASD), more remains to be learned about how symptoms emerge in the first year of life. Parents with a new baby who already had at least one biological child diagnosed with ASD (high-risk) or no family history of ASD (low-risk) completed two measures when their baby was 9 months of age, the Autism Parent Screen for Infants (APSI) questionnaire and the interview-based Parent Concerns Form. Children underwent a blinded independent diagnostic assessment for ASD at age 3 years. Total scores on the APSI and the Parent Concerns Form were both able to independently differentiate high-risk children who were later diagnosed with ASD from other high-risk and low-risk children who were not. Using logistic regression, we found that the total score on the APSI predicted ASD outcomes at age 3 with 70% accuracy, but the Parent Concerns Form did not contribute any unique variance when the APSI was already in the model. The results suggest that the APSI identifies early features predictive of ASD in high-risk infants and can be used to flag them for targeted follow-up and screening.

The objectives were to characterize behavioral signs of autism spectrum disorder (ASD) in younger siblings of diagnosed children (high-risk; HR) and examine classification features of the Autism Observation Scale for Infants (AOSI). Participants (501 HR and 180 low-risk [LR]) were assessed between 6 and 18 months using the AOSI and at age 3 for ASD diagnoses. Total AOSI scores differentiated HR infants later diagnosed with ASD starting at 12 months. ROC analyses identified 12- and 18-month cutoff scores associated with 0.52 sensitivity and 0.74 specificity and 0.73 sensitivity and 0.65 specificity, respectively. Although classification accuracy does not support use as a standalone screen, the AOSI identifies features associated with ASD starting at 6 months and differentiates HR infants with ASD by 12 months.

This study examines the construct validity of the First-Year Inventory 2.0 with respect to other established instruments in a sample of high-risk infant siblings of children with Autism Spectrum Disorder. The First-Year Inventory 2.0 is a parent-report screening instrument designed to identify 12-month-old infants at risk for an eventual diagnosis of Autism Spectrum Disorder and consists of two domains: Social-Communication and Sensory-Regulatory. Although the FirstYear Inventory 2.0's screening psychometrics have been examined, its construct validity has not been investigated. In a sample of 112 high-risk 12-month-olds, we examined the First-Year Inventory 2.0's associations with the Autism Observation Scale for Infants, an observer-based Autism Spectrum Disorder screener, and with other developmental instruments measuring similar areas in social communication and regulatory functioning in young children. Findings generally supported the First-Year Inventory 2.0 associations with other instruments in expected ways. The First-Year Inventory 2.0 Social-Communication domain was notably associated with the Autism Observation Scale for Infant's total score and with language and communication domains of the Vineland and the Mullen. The Sensory-Regulatory domain showed minimal associations with other instruments that only had a few sensory items. Considering different objectives and strengths of assessments, researchers and clinicians are encouraged to utilize a variety of instruments in a comprehensive evaluation of a child.

ObjectiveThe diagnosis of autism spectrum disorder (ASD) has been found to be remarkably stable but few studies have followed children not initially diagnosed with ASD beyond 3 years of age to examine late or delayed diagnoses. The present study used a prospective familial-risk design to identify children who had undergone multiple comprehensive assessments in preschool and were determined to be negative for ASD only to meet criteria for ASD when tested in middle childhood.MethodData were pooled across 3 research teams studying later-born siblings of children with ASD. Fourteen children met inclusion criteria for the late-diagnosed group and were compared with a large sample of high- and low-risk siblings from the same sites who had ASD or typical development (TD) outcomes at 3 years of age.ResultsAs a group, the late-diagnosed children scored between the TD and ASD groups on most measures administered at 3 years and differed significantly from the ASD group on most measures. However, there was significant heterogeneity among the late-diagnosed cases. Seven showed very little evidence of ASD in preschool, whereas 7 demonstrated subtle, subthreshold symptomatology.ConclusionSome children with ASD might present with a subtle phenotype early in life or show a prolonged time course of symptom development. This emphasizes the need for screening and surveillance schedules that extend past 36 months and continued evaluation of any child who presents with atypical early development and/or high-risk status. The findings also shed light on reasons why the mean age of ASD diagnosis remains older than 4 years.