The main clinical features of the GOSR2-associated PME are early-onset ataxia, areflexia, action myoclonus and seizures, scoliosis, elevated creatine kinase levels, relative preservation of cognitive function until the late stages of the disease, and relentless disease course.
Among Hsa21 candidate genes in epilepsy, CSTB, coding for the cystein protease inhibitor cystatin B, is involved in progressive myoclonus epilepsy and ataxia in both mice and human.
CSTB homozygous knockout mice show some parallels to the phenotype of human EPM1 including myoclonic seizures, development of ataxia and neuropathological changes associated with cell loss via apoptosis.