Abstract
Previous research has indicated that children with autism exhibit accelerated head growth (HG) in infancy, although the timing of acceleration varies between studies. We examined infant HG trajectory as a candidate autism endophenotype by studying sibling pairs. We retrospectively obtained serial head orbitofrontal circumference measurements of: a) 48 sibling pairs in which one (n = 28) or both (n = 20) sibs were affected by an autism spectrum disorder (ASD); and b) 85 control male sibling pairs. Rate of HG of ASD subjects was slightly accelerated compared to controls, but the magnitude of difference was below the limit of reliability of standard measurement methods. Sibling intra class correlation for rate of HG was highly statistically significant; the magnitude was significantly stronger among autism-affected families (ICC = .63) than among controls (ICC = .26), p < .01. Infant HG trajectory appears familial—possibly endophenotypic—but was not a reliable marker of autism risk among siblings of ASD probands in this sample.
Highlights
The specific neural mechanisms that underlie autism spectrum disorders (ASD) are not yet known, it is likely that subtle neuroanatomical abnormalities precede the development of observable behavioral symptoms in infants with ASD, and a suggested candidate marker for those abnormalities is the trajectory of brain growth during the first 2 years of life
As would be predicted from the mean rates of change for affected and unaffected siblings of ASD probands, there was no significant correlation between head growth rate and autistic severity as measured by the Social Responsiveness Scale (SRS) in the sibling groups nor was there a significant correlation among probands
An omnibus test of significance of overall difference in growth trajectories just reached statistical significance (p=.04). In this quasi-longitudinal study involving retrospectivelyacquired serial measurements of infant head growth in children with autism spectrum disorders (ASD), their male siblings, and unaffected male sibling pairs, head growth trajectories did not predict which male siblings of index autism cases went on to develop ASD, nor did they predict severity among those affected with clinical-level or subclinical symptomatology
Summary
The specific neural mechanisms that underlie autism spectrum disorders (ASD) are not yet known, it is likely that subtle neuroanatomical abnormalities precede the development of observable behavioral symptoms in infants with ASD, and a suggested candidate marker for those abnormalities is the trajectory of brain growth during the first 2 years of life. Their study suggested that head growth acceleration in autism might begin somewhat later They compared 18–35 month old children diagnosed with autism (n=113) to a normal control group using measurements of a) brain volume (structural MRI), b) retrospectively-obtained head circumference measurements from the time of birth, or c) both. The analyses from both measurement methods supported an increase in the rate of head growth in children with autism beginning at around 12 months of age and persisting through the second year of life. The current study builds on the existing scientific literature on head growth in autism in three specific ways It examined sibling pairs, from 48 ASD-affected families and 85 non-ASD families ascertained in the same geographic region across completely overlapping birth years.
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