3q29 microdeletion syndrome is a rare genetic disorder which results from interstitial microdeletion of a segment on the long arm of chromosome 3. The syndrome is characterized by neurodevelopmental and psychiatric manifestations including intellectual disability, autism spectrum disorder, anxiety, executive function deficits, and psychosis/schizophrenia. Systemic manifestations include ocular issues, gastrointestinal disorders, dental anomalies, and congenital heart defects.

We present a 7-year-old boy with a history of intellectual disability including delayed speech and fine motor abilities, and autism spectrum disorder, who presented with frequent and new onset of complete behavioral arrest, staring, grunting and pulling movements lasting several minutes that were described by his teachers. Spells did not progress to tonic-clonic activity and were not associated with urine loss. His physical examination revealed down slanted eyes, epicanthal folds, wide mouth, long and thin philtrum, thin upper lip and axial and appendulicar tone were decreased. EEG while off ASM revealed excessive beta activity of the background, frontally dominant generalized spike/polyspike and wave discharges, and focal spike/polyspike and wave activity seen independently over the left and right frontocentral regions. MRI showed reduced cerebral white matter hemispheric volume involving the frontoparietal lobes with no obvious seizure focus. He was subsequently started on levetiracetam,which resulted in a cessation of staring spells.

Seizures have been reported in 13% of patients with 3q29 microdeletion syndrome and are generally mild and responsive to ASM. Previously reported EEG abnormalities in patients with 3q29 microdeletion syndrome include focal epileptiform discharges in the left occipital region and slow waves in the frontotemporal regions. To our knowledge, generalized spike/polyspike wave activity has not previously been reported in this syndrome. Whether the independent focal frontocentral epileptiform discharges represent a forme fruste of the generalized discharges, or the latter represent a rapid secondary bisynchrony phenomenon, remains to be determined.