Early generalized overgrowth in boys with autism

Abstract

Context: Multiple studies have reported an overgrowth in head circumference (HC) in the first year of life in autism. However, it is unclear whether this phenomenon is independent of overall body growth and whether it is associated with specific social or cognitive features.

Objectives: To examine the trajectory of early HC growth in autism compared with control groups; to assess whether HC growth in autism is independent of height and weight growth during infancy; and to examine HC growth from birth to 24 months in relationship to social, verbal, cognitive, and adaptive functioning levels.

Design: Retrospective study.

Setting: A specialized university-based clinic.

Participants: Boys diagnosed as having autistic disorder (n = 64), pervasive developmental disorder-not otherwise specified (n = 34), global developmental delay (n = 13), and other developmental problems (n = 18) and typically developing boys (n = 55).

Main outcome measures: Age-related changes in HC, height, and weight between birth and age 24 months; measures of social, verbal, and cognitive functioning at age 2 years.

Results: Compared with typically developing controls, boys with autism were significantly longer by age 4.8 months, had a larger HC by age 9.5 months, and weighed more by age 11.4 months (P = .05 for all). None of the other clinical groups showed a similar overgrowth pattern. Boys with autism who were in the top 10% of overall physical size in infancy exhibited greater severity of social deficits (P = .009) and lower adaptive functioning (P = .03).

Conclusions: Boys with autism experienced accelerated HC growth in the first year of life. However, this phenomenon reflected a generalized process affecting other morphologic features, including height and weight. The study highlights the importance of studying factors that influence not only neuronal development but also skeletal growth in autism.

Figure 1

Spline-based Bayesian multilevel growth curves showing group means for head circumference (HC) (A), height (B), and weight (C) for the autism (AUT), pervasive developmental disorder–not otherwise specified (PDD-NOS), global developmental delay (GDD), Other (OTH), and typically developing (TD) groups from birth to 24 months (left) and zoomed in from 6 to 15 months (right). (For explanation of “Other” see “Participants” subsection of the “Methods” section).

Figure 2

Head circumference (HC) data for the autism (AUT) and typically developing (TD) groups (A), pervasive developmental disorder–not otherwise specified (PDD-NOS) and TD groups (B), global developmental delay (GDD) and TD groups (C), and Other (OTH) and TD groups (D). For each pair, graphs on the left illustrate spline-based Bayesian multilevel growth curves for each of the clinical groups and TD controls. The boundaries represent 95% credible bands. Graphs on the right describe differences between means of a given clinical group and TD controls from birth to 24 months. Divergence of the credible band from 0 represents a significant difference between the means at P≤.05 (2-sided). (For explanation of “Other” see “Participants” subsection of the “Methods” section.)

Figure 3

Differences between means of a given clinical group and typically developing controls for height (left) and weight (right) for autism (A), pervasive developmental disorder–not otherwise specified (B), global developmental delay (C), and other delays (D) from birth to 24 months. Divergence of the credible band from 0 represents a statistically significant difference between the means at the P≤.05 level (2-sided).

Figure 4

Comparison between the autism (AUT) (A) and pervasive developmental disorder–not otherwise specified (PDD-NOS) (B) groups and typically developing (TD) controls on overall body size principal component scores (PC₁). Graphs on the left illustrate spline-based Bayesian multilevel growth curves of the first PC for each comparison group. The boundaries represent 95% credible bands. Graphs on the right show a difference between means for 2 groups from birth to 24 months. Divergence of the 95% credible band from 0 represents a significant difference between the means at P≤.05 (2-sided).

Figure 5

Comparisons between the autism (AUT) (A) and pervasive developmental disorder–not otherwise specified (PDD-NOS) groups and typically developing (TD) controls on the relative head size principal component scores (PC₂). Graphs on the left illustrate spline-based Bayesian multilevel growth curves of the second PC derived by principal component analysis for each comparison group. The boundaries represent 95% credible bands. Graphs on the right show a difference between means for 2 groups from birth to 24 months. Divergence of the 95% credible band from 0 represents a significant difference between the means at the P≤.05 level (2-sided).