disorder to experience a marked deterioratio n in motor symptoms an d display a full cata-
tonic episode with symptoms such as mutism, posturing, grimacing and waxy flexibility.
The risk period for comorbid catatonia appears to be greate st in the adolescent years.
Prevalence 
In recent years, reported frequencies for au tism spectrum disorder  across U.S. and non-
U.S. countries have approached 1% of the po pulation, with similar estimates in child and
adult samples. It remains unclear whether high er rates reflect an expansion of the diag-
nostic criteria of DSM-IV to include subthreshold cases, increased awareness, differences
in study methodology, or a true increase in  the frequency of autism spectrum disorder.
Development and Course
The age and pattern of onset also should be noted for autism spectr um disorder. Symptoms
are typically recognized during th e second year of life (12–24 months of age) but may be seen
earlier than 12 months if developmental delays  are severe, or noted later than 24 months if
symptoms are more subtle. The pattern of onset description might include information
about early developmental delays or any losses of social or language skills. In cases where
skills have been lost, parents or caregivers may give a history of a gradual or relatively
rapid deterioration in social behaviors or lang uage skills. Typically, this would occur be-
tween 12 and 24 months of age and is distinguished from the rare instances of developmen-
tal regression occurring after at least 2 years of normal development (previously described
as childhood disintegrative disorder).
The behavioral features of autism spectrum  disorder first become evident in early
childhood, with some cases presenting a lack of  interest in social interaction in the first
year of life. Some children with autism spectrum disorder experience developmental pla-