Synonym: progressive myoclonus epilepsy of the Lafora type
Inheritance: autosomal recessive
Genes affected: EPM2A or NHLRC1(EPM2B)
Chromosomes: EPM2A on 6q24, NHLRC1 on 6p22.3
EPM2A produces laforin which is a tyrosine phosphatase (with phosphorylase activity)
NHLRC1 produces malin, which may inhib glycogen synthase
Onset: late childhood or adolescence after normal childhood
Clinical features:
(1) one or both of the following
(1a) generalized tonic-clonic seizures, often with status epilepticus
(1b) fragmentary, symmetric or generalized myoclonus
(2) occipital seizures with visual hallucinations
(3) progressive neurologic degeneration (normal at onset, over time develops dysarthria, ataxia, spasiticity, dementia)
Imaging studies of the brain are normal at the onset of symptoms.
EEG shows:
(1) slowing of background activity
(2) photosensitivity
(3) loss of alpha-rhythm
(4) loss of sleep features
Skin biopsy shows periodic acid Schiff (PAS) positive intracellular inclusion bodies (Lafora bodies) formed by accumulation of polyglucosan. Lafora bodies are also seen in other organs (liver, central nervous system).
