Familial myoclonus-1 is an autosomal dominant neurologic condition characterized by adult onset of cortical myoclonus manifest as involuntary jerks or movements affecting the face and limbs. Affected individuals can also experience falls without seizure activity or loss of consciousness (summary by Russell et al., 2012). Genetic Heterogeneity of Familial Myoclonus Also see MYOCL2 (618364), caused by mutation in the SCN8A gene (600702) on chromosome 12q13.

A rare genetic neurological disorder with characteristics of childhood-onset severe myoclonic and tonic-clonic seizures and early-onset ataxia leading to severe gait disturbances associated with normal to slightly diminished cognition. Scoliosis, diffuse muscle atrophy and subcutaneous fat loss, as well as developmental delay, may be associated. Brain MRI may reveal complete agenesis of the corpus callosum, ventriculomegaly, interhemispheric cysts and simplified gyration (frontally).

Progressive myoclonic epilepsy-8 (EPM8) is a rare autosomal recessive form of progressive myoclonic epilepsy with phenotypic variability including ataxia and other movement disorders in addition to myoclonus (summary by Godeiro et al., 2018). For a discussion of genetic heterogeneity of progressive myoclonic epilepsy, see EPM1A (254800).