Approximately 1 in 31 children and 1 in 45 adults are diagnosed as Autistic (1), a highly variable condition characterised by challenges in social skills and restricted, repetitive behaviours present from early childhood (2). At least one third of children later diagnosed as Autistic will have experienced developmental regression – referring to a loss of previously learned skills during childhood (3) with 11% more diagnosed when a broader definition for regression is used (4). Despite being common, regression of skills experienced by Autistic children remains poorly understood and inconsistently managed. World Autism Awareness Day offers an important opportunity to highlight why greater knowledge of developmental regression within Autism is needed to tailor child and family supports and progress our understanding of cause.
There is substantial variation in regression presentation in Autistic children. Some who regress had prior delayed development, whereas others met milestones or were advanced prior to skills loss. The age of onset of regression also varies, with a mean age reported around 18 months old (3), however later and earlier onset is increasingly recognised. Furthermore, motor and functional skills loss, not only social and language loss, are being reported.
Variation in presentation and lack of an agreed definition are two key factors in delay in identification, hindering consistent clinical prioritisation and identification (5). Regression is often only explored once a child is being assessed for Autism, not at the time of the skill loss, missing an opportunity to provide support for each child and family and to explore cause and potential interventions in a timely way.
Families say prognostic uncertainty increases their burden of care (6). Uncertainty is linked to a lack of evidence about cause and difficulties predicting outcomes for each different presentation. Importantly, the trajectories of developmental regain and progress amongst Autistic children who have lost skills is rarely deteriorating, unless a co-occurring condition is identified.
Decades of research into possible Autism subtypes and regression biomarkers have failed to yield conclusive results. Some theories to explain regression refer to a neurocomputational pruning hypothesis (7), others postulate mitochondrial dysfunction (8). Skill loss after expected development has also sparked concern about environmental exposures as the cause. Some possible causes are now disproven, and many have inconsistent, inconclusive research findings, at least in part, because one causal pathway is unlikely given presentation variations.
Research on developmental regression is evolving. Scientists, clinicians and people with lived experience are working together. For example, in the novel Developmental Regression clinic at Monash Children’s Hospital in Melbourne that provides child and family care and support with embedded research, and through emerging international collaborations.
World Autism Awareness Day provides an opportunity to highlight the importance of asking about developmental regression to pave the way for earlier child and family supports, to enable timely investigation and to advance opportunities to generate evidence through collaborative research initiatives to improve care and outcomes.
References
- Shaw KA, Williams S, Patrick ME, et al. Prevalence and Early Identification of Autism Spectrum Disorder Among Children Aged 4 and 8 Years — Autism and Developmental Disabilities Monitoring Network, 16 Sites, United States, 2022. MMWR Surveill Summ 2025;74(No. SS-2):1–22. http://dx.doi.org/10.15585/mmwr.ss7402a1
- American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders (5th ed., text rev.). https://doi.org/10.1176/appi.books.9780890425787
- Tan C, Frewer V, Cox G, Williams K, Ure A. Prevalence and Age of Onset of Regression in Children with Autism Spectrum Disorder: A Systematic Review and Meta-analytical Update. Autism Res. 2021;14(3):582-598. https://doi:10.1002/aur.2463
- Goin-Kochel RP, Esler AN, Kanne SM, Hus V. Developmental regression among children with autism spectrum disorder: Onset, duration, and effects on functional outcomes. Research in autism spectrum disorders. 2014;8(7):890-898. https://doi:10.1016/j.rasd.2014.04.002
- Furley K, Mehra C, Goin-Kochel RP, et al. Developmental regression in children: Current and future directions. Cortex. 2023;169:5-17. https://doi:10.1016/j.cortex.2023.09.001
- Ellis MJ, Larsen K, Havighurst SS. Childhood Disintegrative Disorder (CDD): Symptomatology of the Norwegian Patient Population and Parents’ Experiences of Patient Regression. J Autism Dev Disord. 2022;52(4):1495-1506. https://doi:10.1007/s10803-021-05023-7
- Thomas, M.S.C., Knowland, V.C.P., & Karmiloff-Smith, A. (2011a). Mechanisms of developmental regression in autism and the broader phenotype: a neural network modeling approach. Psychological Review, 118 (4), 637–654.https://doi:10.1037/a0025234
- Frye RE, Rincon N, McCarty PJ, Brister D, Scheck AC, Rossignol DA. Biomarkers of mitochondrial dysfunction in autism spectrum disorder: A systematic review and meta-analysis. Neurobiol Dis. 2024;197:106520. doi:10.1016/j.nbd.2024.106520
Paediatrician researcher currently working in a novel clinic established to assess children experiencing early signs of developmental regression at Monash Children’s Hospital, Melbourne (Australia). She is completing post doctoral research through Monash Health and Monash University to develop innovative ways to improve the earlier detection and diagnostic outcomes for children with developmental regression.
Head of the Department of Paediatrics, Professor Williams is a Paediatrician and Public Health Physician. Her expertise is in neurodevelopmental differences and disabilities, with a focus on autism. Professor Williams’ research uses clinical and population epidemiology to estimate prevalence, find causes, understand prognosis, make accurate diagnoses, and develop effective interventions. She is actively involved in embedding research in health care to create an immediate and sustainable improvement to child health.