Myoclonic occipital photosensitive epilepsy with dystonia (MOPED): A familial epilepsy syndrome

Abstract

Purpose: To describe clinical and EEG phenotypes of a family with an unusual familial epilepsy syndrome characterized by myoclonus and dystonia.

Methods: Family members underwent electroclinical phenotyping including review of EEGs and MRI. DNA from family members was genotyped using Illumina OmniExpress genotyping arrays. Parametric and nonparametric linkage analyses were performed using MERLIN.

Results: The disorder followed autosomal dominant (AD) inheritance and affected seven individuals over two generations. Seizures began at a mean of 14.5 years. Six individuals had spontaneous myoclonic seizures, of which five also had photic-induced myoclonus and four had photic-induced occipital seizures. Six individuals had convulsive seizures; generalized in two and focal in four. Photosensitivity was prominent with generalized spike wave and polyspike wave in four individuals of which two also had occipital spikes. MRI scans were normal in the four individuals tested. Extensive metabolic investigation was normal. Juvenile myoclonic epilepsy (JME) occurred in two; and JME overlapping with idiopathic photosensitive epilepsy (IPOE) in four individuals. All three affected males had a more severe disorder than the four affected females. Two males had a progressive neurological disorder with progressive myoclonus epilepsy and deterioration in their early 30s. They developed episodes of paroxysmal cervical dystonia with cognitive decline during periods of poor seizure control. One plateaued after years of poor seizure control but remained intractable with periods of deterioration. The other deteriorated with episodes of status dystonicus and status epilepticus, ataxia and a progressive ophthalmoplegia before succumbing at 38 years. Parametric linkage analysis identified three peaks achieving a maximum LOD score of 1.21. Nonparametric analysis identified eight peaks achieving LOD scores above 0.80. These were not statistically significant.

Conclusions: This is a novel autosomal dominant familial epilepsy syndrome. "Myoclonic occipital photosensitive epilepsy with dystonia" (MOPED) involves a spectrum of phenotypes from JME, sometimes with an IPOE overlap, to progressive myoclonus epilepsy with paroxysmal dystonia.

Keywords: Genetic; Idiopathic photosensitive occipital epilepsy; Juvenile myoclonic epilepsy; Progressive myoclonus epilepsy.