ABSTRACT
Abstract The very earliest description by Kanner indicated that large head size was associated with autism spectrum disorder. Yet, since then, opinion has ranged from those who argue that head and brain size is a general feature of autism spectrum disorder (ASD) to those who posit that this association is an artifact. We selectively review the literature on macrocephaly and megalencephaly in ASD and come to the conclusion that head and brain enlargement is characteristic of only a subset of approximately 15% of males with ASD. It appears that this is much less common in females. Moreover, the widespread notion that early macrocephaly
Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 10.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 10.2 Studies of macrocephaly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 10.3 Studies of megalencephaly . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 10.4 Brain enlargement in a subsample of individuals with ASD. . 175 10.5 Sex differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 10.6 Body size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 10.7 Normalization of brain size . . . . . . . . . . . . . . . . . . . . . . . . . . 178 10.8 Neurobiology of brain enlargement . . . . . . . . . . . . . . . . . . . . 178 10.9 Microcephaly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 10.10 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
and megalencephaly is followed by normalization of head/brain size is not supported by essential longitudinal studies. Given that an enlarged brain is a feature of one form of ASD, the critical remaining issues are what causes the abnormal brain enlargement and whether this has consequences on the clinical and cognitive outcomes of the affected individuals.
