Introduction: Familial cortical myoclonic tremor with epilepsy (FCMTE) is defined by an autosomal-dominant inheritance, adult onset of myoclonus of the extremities, infrequent epileptic seizures, a non-progressive course, polyspikes on electroencephalography (EEG), photosensitivity, giant somatosensory-evoked potentials (SEP), enhancement of C-reflex and a premyoclonus spike detected by jerk-locked EEG back-averaging. Two genes yet to be identified are mapped to 8q23.3-q24.1 and 2p11.1-q12.2.
Methods: The present study involved five generations of a French family presenting with FCMTE, including 76 family members. Clinical analyses were performed in 39 living subjects and electrophysiological studies in five patients. Altogether, 27 relatives (21 living and six deceased) had the clinical characteristics of FCMTE, 17 of whom were analyzed. Linkage analyses were performed with microsatellites encompassing the two known loci (8q 23.3-q24.1 and 2p11.1-q12.2).
Results: Mean age at onset in the 17 living patients was 28.8 years (range 24-41). All had myoclonus/cortical tremor, and 11/17 had generalized tonic-clonic seizures. Other clinical symptoms were photosensitivity (16 cases), partial seizures (five cases), sensitivity to starvation/exercise (six cases) and vibration (four cases), ophthalmic migraine (six cases) and gait disorders (10 cases). Electrophysiological studies confirmed the FCMTE diagnosis in the five studied patients. Of the remaining relatives, 14 were considered healthy (asymptomatic subjects aged more than 40years) and eight were of unknown status (asymptomatic aged lesser than 40years). The pattern of inheritance was consistent with autosomal-dominant inheritance, although the two loci responsible for FCMTE were excluded.
Conclusion: This large family highlights some unusual clinical characteristics and suggests the presence of a third gene. Genetic research is ongoing to identify the mutated gene.