Poor data produce poor models: children with developmental disabilities deserve better
Authors: Diane Damiano, Hans Forssberg
Journal: The Lancet Global Health (2019)

Although we concur with the crucial need for baseline data for the global prevalence of developmental disabilities, we believe it is imperative that these data are accurate. The majority of children with disabilities live in low-income and middle-income countries (LMICs), but data for many regions are unavailable or inaccurate and no amount of sophisticated modelling can compensate for poor primary data sources. Therefore, we contend that the calculation of the Global Burden of Disease (GBD) for developmental disabilities (October, 2018)1Global Research on Developmental Disabilities CollaboratorsDevelopmental disabilities among children younger than 5 years in 195 countries and territories, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016.Lancet Glob Health. 2018; 6: e1100-e1121Summary Full Text Full Text PDF PubMed Scopus (263) Google Scholar does not reflect the true global burden or its distribution. Evolving research on neurodevelopmental disorders from high-income countries (HICs) has deepened our understanding of their cause and epidemiology, which can be extrapolated to LMICs. Many neurodevelopmental disorders result from complex gene–environment interactions during early brain development, including attention deficit hyperactivity disorder (ADHD), which is present in about 5% of children and has little geographic or ethnic variation in prevalence.2Faraone SV Larsson H Genetics of attention deficit hyperactivity disorder.Mol Psychiatry. 2018; 14: R275-R282Google Scholar Genome-wide association studies have identified multiple risk genes with an estimated heritability of 74%. ADHD is considered the extreme end of the normal population distribution with increasing prevalence partly explained by decreased threshold for diagnosis. Global prevalence reported in the GBD study was 0·14%, but it was 5% in HICs. This discrepancy is probably due to large differences in sampling and diagnostic thresholds. Other neurodevelopmental disorders also have a strong polygenic influence. Autism spectrum disorder, which has a heritability of 50%, would be expected to have a similar prevalence range between LMICs and HICs. Its prevalence is 1·68% in 8-year-old children in the USA,3Baio J Wiggins L Christensen DL et al.Prevalence of autism spectrum disorder among children aged 8 years—Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2014.MMWR Surveill Summ. 2018; 67: 1-23Crossref PubMed Scopus (2311) Google Scholar similar to GBD data from Sweden. The far lower 0·72% global estimate in the GBD study does not appear plausible given similar or more abundant risk factors in LMICs. The inclusion of cerebral palsy within the category of intellectual disabilities rather than as a unique category is a major shortcoming in the GBD study. Cerebral palsy is primarily a motor disorder with a prevalence of 0·2% in HICs. For most children with cerebral palsy, the burden of disease is large and therefore warrants inclusion as a separate health condition in the GBD study. Accumulating evidence suggests that this disorder is also a polygenic complex disorder, with hereditability around 30%, indicating that environmental risk factors can play a major causative role. In a recent population-based study from rural Uganda,4Kakooza-Mwesige A Andrews C Peterson S Wabwire Mangen F Eliasson AC Forssberg H Prevalence of cerebral palsy in Uganda: a population-based study.Lancet Glob Health. 2017; 5: e1275-e1282Summary Full Text Full Text PDF PubMed Scopus (80) Google Scholar prevalence of cerebral palsy in children aged 2–6 years was twice as high in Uganda (0·4%) as in HICs, reflecting a different panorama of increased risk factors LMICs.4Kakooza-Mwesige A Andrews C Peterson S Wabwire Mangen F Eliasson AC Forssberg H Prevalence of cerebral palsy in Uganda: a population-based study.Lancet Glob Health. 2017; 5: e1275-e1282Summary Full Text Full Text PDF PubMed Scopus (80) Google Scholar By contrast, the prevalences of hearing (3·99%) and visual impairments (2·45%) reported in LMICs in the GBD study are astonishingly high compared with those in HICs. A study from the US Centers for Disease Control and Prevention5Boyle CA Boulet S Schieve LA et al.Trends in the prevalence of developmental disabilities in US children, 1997–2008.Pediatrics. 2011; 127: 1034-1042Crossref PubMed Scopus (1166) Google Scholar reported prevalences of 0·38% for hearing and 0·13% for vision in the USA.5Boyle CA Boulet S Schieve LA et al.Trends in the prevalence of developmental disabilities in US children, 1997–2008.Pediatrics. 2011; 127: 1034-1042Crossref PubMed Scopus (1166) Google Scholar Although more infectious causes of hearing and vision loss are present in LMICs than in HICs, criteria for reporting probably differ across settings and might include causes routinely treated in HICs such as otitis, wax plugs, or refractory abnormalities. Increased survival in children younger than 5 years is a major global accomplishment, but also a challenge since many surviving children will experience lifelong disabilities limiting their full participation in society. They must be identified and accurately accounted for so that true progress achieved in ameliorating the burden of these conditions is verifiable. More population-based studies in LMICs are imperative. In their absence, reliance on such studies in similar regions might provide more reliable estimates than data from less rigorous methodologies. We declare no competing interests. Developmental disabilities among children younger than 5 years in 195 countries and territories, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016The global burden of developmental disabilities has not significantly improved since 1990, suggesting inadequate global attention on the developmental potential of children who survived childhood as a result of child survival programmes, particularly in sub-Saharan Africa and south Asia. The SDGs provide a framework for policy and action to address the needs of children with or at risk of developmental disabilities, particularly in resource-poor countries. Full-Text PDF Open AccessPoor data produce poor models: children with developmental disabilities deserve better – Authors' replyIn commenting on our study,1 Diane Damiano and Hans Forssberg aptly acknowledge the lifelong disabilities faced by many beneficiaries of under-5-survival programmes and the need for baseline data to monitor interventions under the Sustainable Development Goal (SDG) era. Our Global Burden of Disease (GBD) study1 aimed to provide, for the first time ever, essential baseline data for six prominent developmental disabilities across 195 countries from 1990 to 2016, bridging a critical gap in the global developmental epidemiology. Full-Text PDF Open Access