Autism spectrum disorder in the second year: stability and change in syndrome expression.

Objectives: Increasing numbers of young children referred for a differential diagnosis of autism spectrum disorders (ASD) necessitates better understanding of the early syndrome expression and the utility of the existing state-of-the art diagnostic methods in this population. Method: Out of 31 infants under the age of 2 years referred for a differential diagnosis, 19 were diagnosed with autism, and 9 with pervasive developmental disorder – not otherwise specified (PDD-NOS) when reassessed at 3 years. We examined 1) the symptoms of ASD in the second year and changes in the syndrome expression by the age of three; 2) relationship between expert-assigned clinical diagnosis and diagnostic classification based on Autism Diagnostic Observation Schedule-Generic (ADOS-G) and Autism Diagnostic InterviewRevised (ADI-R) in the second year; 3) the relationship between direct observation and parental report of ASD symptoms. Results: Symptoms of autism and PDD-NOS in the second year were pronounced and stability of the clinical diagnosis was high. The agreement between clinician-assigned autism but not PDD-NOS diagnosis and the ADOS-G was high. However, sensitivity of the ADI-R diagnostic classification of autism was poor. Comparison of concurrent parental report and direct observation revealed discrepancies in severity ratings of key dyadic social behaviors. Changes in communication reflected acquisition of language accompanied by the emergence of unusual language characteristics. Symptoms of social dysfunction were relatively stable over time, and so was the severity of stereotyped behaviors. Conclusions: The study provides support for stability of clinical diagnosis and syndrome expression in the second year and highlights advantages and limitations of the ADI-R and ADOS-G for diagnosing and documenting symptoms of ASD in infants. Keywords: Autism, ASD, PDD-NOS, early diagnosis, ADOS-G, ADI-R, infants, toddlers, assessment, longitudinal studies. Growing awareness of symptoms of autism spectrum disorders (ASD) in young children among parents and professionals, as well as close monitoring of infants at familial risk for developing ASD, result in a rapidly increasing number of infants and toddlers being referred to specialized clinics for a differential diagnosis. Therefore, better understanding of the syndrome’s expression in the first years of life and the utility of the existing state-of-the art diagnostic methods in this population is essential (Klin, Chawarska, Rubin, & Volkmar, 2003; Volkmar, Lord, Bailey, Schultz, & Klin, 2004). While autism has not usually been diagnosed until the age of 3 to 4 years (Chakrabarti & Fombonne, 2005, 2001; Charman & Baird, 2002; Filipek et al., 1999), a majority of parents voice their concerns before their child’s second birthday, and about 50% notice some abnormalities in the first year (Volkmar, Stier, & Cohen, 1985). Nonetheless, evidence regarding early developmental course of ASD is still limited due to scarcity of prospective follow-up studies. The first study to report on developmental course of a very small group of infant siblings at high risk for ASD suggest that symptoms of autism might be noticeable at six months and that by 12 months, they might include abnormalities in visual attention and eye contact,impairedorientingtoname,delaysinspeechand