Which neurodevelopmental disorders get researched and why?

Abstract

Aim: There are substantial differences in the amount of research concerned with different disorders. This paper considers why.

Methods: Bibliographic searches were conducted to identify publications (1985-2009) concerned with 35 neurodevelopmental disorders: Developmental dyslexia, Developmental dyscalculia, Developmental coordination disorder, Speech sound disorder, Specific language impairment, Attention deficit hyperactivity disorder, Autistic spectrum disorder, Tourette syndrome, Intellectual disability, Angelman syndrome, Cerebral palsy, Cornelia de Lange syndrome, Cri du chat syndrome, Down syndrome, Duchenne muscular dystrophy, Fetal alcohol syndrome, Fragile X syndrome, Galactosaemia, Klinefelter syndrome, Lesch-Nyhan syndrome, Lowe syndrome, Marfan syndrome, Neurofibromatosis type 1, Noonan syndrome, Phenylketonuria, Prader-Willi syndrome, Rett syndrome, Rubinstein-Taybi syndrome, Trisomy 18, Tuberous sclerosis, Turner syndrome, Velocardiofacial syndrome, Williams syndrome, XXX and XYY. A publication index reflecting N publications relative to prevalence was derived.

Results: The publication index was higher for rare than common conditions. However, this was partly explained by the tendency for rare disorders to be more severe.

Interpretation: Although research activity is predictable from severity and prevalence, there are exceptions. Low rates of research, and relatively low levels of NIH funding, characterise conditions that are the domain of a single discipline with limited research resources. Growth in research is not explained by severity, and was exceptionally steep for autism and ADHD.

Figure 1. Regression of log publication index on log severity, with 95% confidence interval shown with dotted lines.

A constant of 4 is added to log publication index to avoid negative numbers. Abbreviations: ADHD: attention deficit hyperactivity disorder; ASD: autism spectrum disorder; CP: cerebral palsy; DCD: developmental co-ordination disorder; de Lange: Cornelia de Lange syndrome; FraX: fragile X; ID: intellectual disability (shown in brackets to indicate that the publication index is overestimated); NF1: neurofibromatosis type 1; PKU: phenylketonuria; SLI: specific language impairment; T. sclerosis: tuberous sclerosis; VCF: velocardiofacial syndrome.

Figure 2. Proportion of grant income from different NIH institutes for the most common neurodevelopmental disorders.

Abbreviations: NIMH: National Institute of Mental Health; NINDS: National Institute of Neurological Disorders and Stroke; NIDCD: National Institute on Deafness and Other Communication DIsorders; NICHD: Eunice Kennedy Shriver National Institute of Child Health and Human Development.