Age of walking and intellectual ability in autism spectrum disorder and other neurodevelopmental disorders: a population-based study

Alexandra Havdahl^{1

2

3

4}, Cristan Farmer⁵, Synnve Schjølberg², Anne-Siri Øyen^{1

2}, Pål Surén², Ted Reichborn-Kjennerud², Per Magnus², Michaeline Bresnahan^{6

7}, Mady Hornig⁷, Ezra Susser^{6

7}, W Ian Lipkin^{7

8}, Catherine Lord⁹, Camilla Stoltenberg^{2

10}, Audrey Thurm⁵, Somer Bishop¹¹

Affiliations

¹ Nic Waals Institute, Lovisenberg Diaconal Hospital, Oslo, Norway.
² Norwegian Institute of Public Health, Oslo, Norway.
³ MRC Integrative Epidemiology Unit, Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK.
⁴ PROMENTA Research Center, Department of Psychology, University of Oslo, Oslo, Norway.
⁵ Pediatrics & Developmental Neuroscience Branch, National Institute of Mental Health, Bethesda, MD, USA.
⁶ New York State Psychiatric Institute, Columbia University Medical Center, New York, NY, USA.
⁷ Department of Epidemiology, Mailman School of Public Health, New York, NY, USA.
⁸ Center for Infection and Immunity, Mailman School of Public Health and Departments of Neurology and Pathology, Vagelos College of Physicians and Surgeons of Columbia University, New York, NY, USA.
⁹ David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA.
¹⁰ Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.
¹¹ UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA.

PMID: 33369747
PMCID: PMC8236490
DOI: 10.1111/jcpp.13369

Age of walking and intellectual ability in autism spectrum disorder and other neurodevelopmental disorders: a population-based study

Alexandra Havdahl et al. J Child Psychol Psychiatry. 2021 Sep.

. 2021 Sep;62(9):1070-1078.

doi: 10.1111/jcpp.13369. Epub 2020 Dec 28.

Authors

Affiliations

¹ Nic Waals Institute, Lovisenberg Diaconal Hospital, Oslo, Norway.
² Norwegian Institute of Public Health, Oslo, Norway.
³ MRC Integrative Epidemiology Unit, Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK.
⁴ PROMENTA Research Center, Department of Psychology, University of Oslo, Oslo, Norway.
⁵ Pediatrics & Developmental Neuroscience Branch, National Institute of Mental Health, Bethesda, MD, USA.
⁶ New York State Psychiatric Institute, Columbia University Medical Center, New York, NY, USA.
⁷ Department of Epidemiology, Mailman School of Public Health, New York, NY, USA.
⁸ Center for Infection and Immunity, Mailman School of Public Health and Departments of Neurology and Pathology, Vagelos College of Physicians and Surgeons of Columbia University, New York, NY, USA.
⁹ David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA.
¹⁰ Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.
¹¹ UCSF Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA, USA.

PMID: 33369747
PMCID: PMC8236490
DOI: 10.1111/jcpp.13369

Abstract

Background: Delayed walking is common in intellectual disability (ID) but may be less common when ID occurs with autism spectrum disorder (ASD). Previous studies examining this were limited by reliance on clinical samples and exclusion of children with severe motor deficits.

Objective: To examine in a population-based sample if age of walking is differentially related to intellectual ability in children with ASD versus other neurodevelopmental disorders (NDD).

Methods: Participants were from the nested Autism Birth Cohort Study of the Norwegian Mother, Father and Child Cohort Study (MoBa). Cox proportional hazards regression assessed if diagnosis (ASD n = 212 vs. NDD n = 354), continuous nonverbal IQ, and their interaction, were associated with continuous age of walking.

Results: The relationship between nonverbal IQ and age of walking was stronger for NDD than for ASD (Group × nonverbal IQ interaction, χ² = 13.93, p = .0002). This interaction was characterized by a 21% decrease in the likelihood of walking onset at any given time during the observation period per 10-point decrease in nonverbal IQ (hazard ratio = 0.79, 95% CI: 0.78-0.85) in the NDD group compared to 8% (hazard ratio = 0.92, 95% CI: 0.86-0.98) in the ASD group.

Conclusions: The finding that age of walking is less strongly related to low intellectual ability in children with ASD than in children without other NDDs supports the hypothesis that ID in ASD may result from heterogeneous developmental pathways. Late walking may be a useful stratification variable in etiological research focused on ASD and other NDDs.

Keywords: Intellectual disability; MoBa; epidemiology; gross motor milestones; late walking.

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Conflict of interest statement

Conflicts of Interest:

Drs. Bishop and Lord have received royalties from the ADOS-2. All profits from their research are donated to charity. The other authors report no conflicts of interest.

Figures

**Figure 1.. Participant flow**
**Note:** Of the children invited to participate in the ABC study based on selection criteria, one child did not complete the assessment and one child had Rett syndrome. Both were therefore excluded. ASD=autism spectrum disorder. NDD=neurodevelopmental disorders without ASD. IQ=intelligence quotient. MoBa=the Norwegian Mother, Father and Child Cohort Study. Of the children without any clinical diagnosis (n=454), 444 children had data on walking and IQ. ASD included ABC Protocol ASD diagnosis as of 19 Oct 2014 (Autistic Disorder, Asperger Disorder and Pervasive Developmental Disorder Not Otherwise Specified), childhood disintegrative disorder and profound disability with autism.*Rett syndrome was excluded (n=2) because of insufficient information on whether ASD diagnostic criteria were met (i.e., for either Autistic Disorder or PDD-NOS).

**Figure 2.. Illustration of differential relationship between nonverbal IQ and age of walking for NDD and ASD groups**
**Note:** Plotted values are model-estimated probabilities of walking at a given age (X-axis) and given value for nonverbal IQ (line color). IQ was not categorized for analysis or for plotting; instead, the model was used to generate the estimated probability of walking at the given IQ values.

See this image and copyright information in PMC

References

1. Amaral DG, Anderson GM, Bailey A, Bernier R, Bishop S, Blatt G, … Whitehouse A (2019). Gaps in Current Autism Research: The Thoughts of the Autism Research Editorial Board and Associate Editors. Autism Res, 12(5), 700–714. doi: 10.1002/aur.2101 - DOI - PubMed
1. American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC.
1. American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed., text rev.). Washington, DC.
1. American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). Arlington, VA: American Psychiatric Publishing.
1. Anderson DK, Lord C, Risi S, DiLavore PS, Shulman C, Thurm A, … Pickles A (2007). Patterns of growth in verbal abilities among children with autism spectrum disorder. J Consult Clin Psychol, 75(4), 594–604. doi: 10.1037/0022-006X.75.4.594 - DOI - PubMed

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Age of walking and intellectual ability in autism spectrum disorder and other neurodevelopmental disorders: a population-based study

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Age of walking and intellectual ability in autism spectrum disorder and other neurodevelopmental disorders: a population-based study

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Conflict of interest statement

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