Head circumference and height in autism: a study by the Collaborative Program of Excellence in Autism

Abstract

Data from 10 sites of the NICHD/NIDCD Collaborative Programs of Excellence in Autism were combined to study the distribution of head circumference and relationship to demographic and clinical variables. Three hundred thirty-eight probands with autism-spectrum disorder (ASD) including 208 probands with autism were studied along with 147 parents, 149 siblings, and typically developing controls. ASDs were diagnosed, and head circumference and clinical variables measured in a standardized manner across all sites. All subjects with autism met ADI-R, ADOS-G, DSM-IV, and ICD-10 criteria. The results show the distribution of standardized head circumference in autism is normal in shape, and the mean, variance, and rate of macrocephaly but not microcephaly are increased. Head circumference tends to be large relative to height in autism. No site, gender, age, SES, verbal, or non-verbal IQ effects were present in the autism sample. In addition to autism itself, standardized height and average parental head circumference were the most important factors predicting head circumference in individuals with autism. Mean standardized head circumference and rates of macrocephaly were similar in probands with autism and their parents. Increased head circumference was associated with a higher (more severe) ADI-R social algorithm score. Macrocephaly is associated with delayed onset of language. Although mean head circumference and rates of macrocephaly are increased in autism, a high degree of variability is present, underscoring the complex clinical heterogeneity of the disorder. The wide distribution of head circumference in autism has major implications for genetic, neuroimaging, and other neurobiological research.

Fig. 1

The distribution of standardized head circumference in autism probands.

Fig. 2

The distribution of standardized heights in autism probands.

Fig. 3

The relationship of standardized head circumference and height in autism probands.

Fig. 4

The distribution of the difference between standardized head circumference and height (zHC–zHgt) in autism probands.

Fig. 5

Relationship of standardized head circumference and age in autism probands during childhood and adolescence.

Fig. 6

Scatterplot of autism proband zHC and average parental zHC.

Fig. 7

Mean zHC of all ASD probands, cognitively high-functioning and low-functioning autism probands, PDD-NOS probands, and typically developing controls. ASD, all autism-spectrum disorder probands; HFA, cognitively higher-functioning autism probands (pIQ > 70); LFA: cognitively lower-functioning autism probands (pIQ < 70); PDD, probands with pervasive developmental disorder, not otherwise specified (PDD-NOS); Controls: typically developing individuals.

Fig. 8

Rate of macrocephaly (percent) in all ASD probands, cognitively high-functioning and low-functioning autism probands, PDD-NOS probands, and typically developing controls.

Fig. 9

Mean zHC in Autism Families: High- and low-functioning Autism probands, mothers, fathers, affected, and unaffected siblings.

Fig. 10

Rate of macrocephaly (percent) in Autism families: high- and low-functioning autism probands, mothers, fathers, affected, and unaffected siblings.