• INCLUSION CRITERIA:

The sample at study endpoint will contain 50 children diagnosed with idiopathic autism and regression (AUT-R), 50 children diagnosed with idiopathic autism (and no history of regression; AUT-NR), 25 children with Rett's Disorder (RTT) and 50 typically developing children (TYP), matched on ethnicity, sex, chronological age and daycare enrollment. Matching for daycare setting (home versus setting with other children) will be attempted due to the potentially greater immunologic challenge experienced by children in daycare settings. The age range of all groups will be between 12 and 48 months at first visit (with the exception of the RTT group, which will include children up to age 6). We will over-recruit for children in the 12-36 month age range, in order to maximize participants of the age when regression associated with the autism diagnosis is most likely.

The Phenome Project Pilot will also enroll an additional 40 children with autism and 25 age-/sex-matched healthy controls, aged 2-6. In addition, as many as 25 children (ages 2 - 6 years) with developmental delays (without autism) will be recruited as contrast subjects.

Regression will be defined as:

Language loss: Loss of at least 3 spontaneously meaningful words (excluding mama or dada) used for at least a month, and lost for at least a month.

AND/OR

Nonverbal communication/social loss: Loss of more than one nonverbal communicative behavior (e.g. gestures, joint attention, eye contact, imagination, pretend play, sharing, showing, watching children, orienting to name, social smiling, social games, spontaneous imitation of actions, response to social overtures).

Autism groups (AUT-R & AUT-NR): Children with a diagnosis of autism or referral from professional with concerns of a diagnosis of autism will be evaluated with the ADI-R and ADOS. Those meeting research criteria for autism will be included.

Although there is overlap in the age period for regression specified in this protocol (regression between 15-30 months) and that described for childhood disintegrative disorder (CDD) (the DSM-IV criteria for CDD indicate apparently normal development for the first 2 years after birth), the criteria for CDD also indicate a diagnosis can only be made if symptoms are not better accounted for by another pervasive developmental disorder such as autism. Symptoms of CDD that separate it from autism include loss of acquired skills in areas such as motor skills and bowel or bladder control, while the focus of the current study is on regression in core symptoms of autism (i.e. socio-communicative skills). Thus, the current protocol will include children with regression over 2 who meet criteria for autism, but not those who only meet criteria for CDD.

Rett's Disorder group (RTT): Positive genetic screen for MeCP2 genetic mutation.

Typically Developing control group (TYP): No diagnosis of developmental delay and no first-degree relatives with history of developmental problems.

Developmental Delay group (DD): Developmental scores (Performance Quotient and Verbal Quotient) greater than 1.5 standard deviations below mean on Mullen Scales of Early Learning

EXCLUSION CRITERIA:

1. Significant prematurity at birth (less than 32 weeks gestation); birthweight significantly below normal for gestational age (SGA- small for gestational age); or diagnosis of cerebral palsy.
2. If behavioral management issues (e.g. self-injury, aggressiveness) are severe to the extent that the screening protocol was aborted.