The clinical characteristics of 177 children (82% male and 18% female) with language regression were identified and studied prospectively at four medical centers: Montefiore and Albert Einstein, New York, NY; St Louis Children’s, MO; Miami Children’s, FL; and Yale University, CT. Mean age at language regression was 22.8 months (range 12-78 months). Triggers, including family stress, birth of a sibling, moving, seizures, and infection, were identified in 29%. Time to referral to a specialist was 40 months (range 1 month to 14 years). Autistic spectrum disorder, definite (127) or suspect (28), was diagnosed in a total of 88%. Language regression at a younger age (<36 months) in 158 children correlated with a higher probability of autistic regression (91%) than in the 19 with language regression after 36 months (58%). Males with language regression developed autism more commonly than affected females (90% and 75%, respectively).
Seizures occurred in 18%, and EEG abnormalities in 37%. Seizures were more common in children who showed language regression at an older age (53% cf 14%, respectively). Autistic regression was more common in children without seizures, especially after age 36 months. At the time of the last visit, language was impaired in 88%, but some improvement had occurred in 57%. Cognition was definitely abnormal in 28%, and autism was present in 72%. 
COMMENT. The loss of previously acquired language in young children is the most prominent feature of autistic regression and Landau Kleffner syndrome and requires early specialized evaluation and intervention. The most common age for regression to occur is in the second year, but referral to a pediatric neurologist or child psychiatrist is often delayed for 3 or 4 years, when regression has become more global and associated with cognitive and behavioral disorders, seizures, and autism. An EEG to rule out ESES and Landau Kleffner syndrome could lead to early steroid trials and possible surgical treatment. The occurrence of seizures and EEG abnormalities, often associated with autistic regression, might require treatment with antiepileptic drugs.