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AAP Grand Rounds 18:64 (2007)
© 2007 American Academy of Pediatrics
The relationship between infant developmental milestones and later intellectual function was determined in a representative sample of 5,362 children born in the United Kingdom in 1946 and followed into adulthood by researchers at the Behavioral and Clinical Neuroscience Institute, University of Cambridge, and University College London.
When study participants reached two years of age, mothers were asked about the ages at which their child was first able to stand unassisted, walk, and say words. Nonverbal reasoning, reading comprehension, word pronunciation, and vocabulary were examined at age eight. As adults, the study participants were tested on reading comprehension at age 26 and verbal fluency and general intellectual function at age 53. The highest educational or training qualification achieved by age 26 was categorized using the British system of ordinary or advanced secondary education levels.
Information on at least one cognitive score (IQ at age eight, reading comprehension at age 26, or verbal fluency at age 53) and at least one developmental variable was available in 3,969 subjects. Linear modeling demonstrated that earlier motor and speech development were significantly associated with greater IQ at age eight, higher reading comprehension at age 26, and better verbal fluency at age 57.
On average, for every month earlier that a child learned to stand, the individual gained one half of one IQ point as measured at age eight. The effect on reading was not solely driven by late developers. Speech development was related to reading comprehension at age 26 even when late developers were excluded. Later speech developers were less likely to progress beyond basic education. The authors conclude that the age at which infant developmental milestones are attained is associated with subsequent general intellectual function.
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Commentary by
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| Neurology, Children’s Memorial Hospital, Northwestern University Medical School, Chicago, IL |
Later development of motor milestones and speech is associated with a small but statistically significant impairment of intellectual function and educational attainment. The authors postulate a connection between delayed development of cortical-subcortical circuits in infancy and later cognitive dysfunction. A correlation between severe delay in developmental milestones and subsequent learning disability or mental retardation is well documented.1
In contrast, in the normal population it has been assumed that mild to moderate modifications of motor and speech developmental milestones are not related to later intellectual function. In a recent longitudinal birth cohort study by the Cambridge group of a Finnish population-based sample, it was found that more rapid infant motor development is linked to better school performance and higher adult IQ scores.2
Frontal cortex, basal ganglia, and cerebellum volume is linearly related to the speed of infant motor development, according to one recent report.3 This importance of developmental milestone attainment in the prediction of later educational attainment is also suggested by earlier but smaller nonepidemiological samples cited by the authors. In one report of a primary care cohort of 213 children, the age of learning to walk (a milestone most frequently remembered by a parent) was significantly associated with IQ at age three.4 Since delayed milestones of development may predict later intellectual impairment and poor school performance, a careful early history of age of walking and talking may suggest the need for preventive intervention with academic accommodations.
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