“Tapping-evoked spikes” in a patient with Angelman syndrome

A 14-year-old boy, affected by Angelman syndrome and epilepsy, was seizure-free for five years. The repetitive tactile stimulation of the four limbs induced tapping-evoked spikes contralaterally to the stimulation side (figure 1). Somatosensory or tapping-evoked spikes were originally described in normal children and in children suffering from idiopathic epilepsy with rolandic spikes as "extreme somatosensory evoked potentials” (De Marco and Tassinari, 1981). They have also been observed in conditions characterized by cortical hyper-excitability, such as epilepsy associated with Fragile X syndrome and in Rettsyndrome (Musumeci et al., 1994; Guerrini et al., 1998). This phenomenon has never been described in Angelman syndrome. Our observation supports the hypothesis that a GABAergic dysfunction underlies this syndrome, leading to a cortico-thalamic hypersynchronismwith subsequent alteration in processing of sensory inputs (Handforth et al., 2005).