Smith-Magenis syndrome is a multiple congenital anomalies/mental retardation syndrome associated with a heterozygous deletion of chromosome 17p11.2. Seizures have not been formally studied in this population. Our objectives were to estimate the prevalence of seizures and electroencephalographic (EEG) epileptiform abnormalities in patients with Smith-Magenis syndrome with defined chromosomal rearrangements and to describe the spectrum of abnormal EEG patterns. Prolonged video-EEGs were obtained in 60 patients. Eighteen percent of patients reported a seizure history; however, abnormal EEGs were identified in 31 of the 60 subjects and 27 of 31 were epileptiform. Generalized epileptiform patterns were the most common (73%). Most patients with either small or large deletions had an abnormal EEG (83%; 75%) in contrast to those with a common deletion (49%). Our results indicate that epileptiform EEG abnormalities are frequent in patients with Smith-Magenis syndrome. Considering that close to one third of individuals with Smith-Magenis syndrome with epileptiform abnormalities also had a history of clinical seizures, cortical hyperexcitability and epilepsy should be considered an important component of the Smith-Magenis syndrome clinical phenotype. ( J Child Neurol 2006;21:93—98; DOI 10.2310/7010.2006.00030).
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