The name is absent

Autism prodrome 28 of 89

trajectory of a prodrome has been identified. To date, most of these high risk sibling
studies have examined the extent to which isolated behavioral abnormalities map onto
an ASD ‘outcome'. In future work groups will likely begin to examine whether
combinations of abnormalities, for example those at risk siblings showing
impairments on both social (eye gaze; orienting to name) and non-social (motor,
attentional control) measures, might be better predictors of developing an ASD, and
thus constitute a kind of ‘cumulative risk’ ASD prodrome or marker.

-------------------Table 3 about here-------------------

Brain development and the prodrome of ASD

There is also considerable interest in identifying structural neuroanatomical
associations of ASD, in particular those that might characterize individuals at risk of
development ASD before the onset of frank diagnostic symptoms. One candidate has
emerged over the past 5 years that of enlarged brain size; in particular a number of
lines of evidence that brain growth trajectory might be abnormal in early
development.

There had been long recognition that increased brain size (often assumed on
the basis of head circumference measurements; an assumption that has empirical
validity (Hazlett et al., 2005)) was more common than expected in clinical samples of
children and adults with ASD; with rates of macrocephaly (head size greater than 2
standard deviations above the norm) in the range of 15%-30% (Bailey et al., 1995;
Bolton et al., 1994; Davidovitch, Patterson, & Gartside, 1996; Woodhouse et al.,
1996; see Lainhart, 2006, for a review). However, head circumference and magnetic
resonance imaging studies find stronger associations in children than in adults and
macrocephaly has not been found in all samples (Redcay & Courchesne, 2005). A
notable study by Courshene et al. (2003) found that head circumference was smaller

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