Within a couple of years, a wheelchair is required for locomotion and within five to ten years, the person is confined to bed and is often tube fed. Valproic acid and zonisamide are first choice anticonvulsants, and the ketogenic diet may be helpful. An autosomal-recessive genetic defect is responsible, which has been tracked down to two genes. The EPM2A gene on chromosome 6q24 was discovered in 1998 and encodes for the protein laforin. It is responsible for 80% of cases. The EPM2B gene on chromosome 6p22.3 was discovered in 2003 and encodes for the protein malin. There may be a third gene of unknown locus. Neuronal ceroid lipofuscinoses
There are various forms of these disorders, each with their own genetic cause and geographical variation, which lead to accumulation of lipopigments (lipofuscin) in the bodys tissues and are inherited in an autosomal-recessive fashion. Onset and symptoms vary with the particular form, but death usually occurs within five to fifteen years. Type I sialidosis
This is an autosomal recessive disorder in which the body is deficient in α-neuraminidase. Myoclonic epilepsy and ataxia due to potassium (K+) channel mutation (MEAK)
MEAK is a form of progressive myoclonus epilepsy that typically begins between the ages of 3 and 15 years (the average of onset is 10 years). The first symptoms may include ataxia and myoclonus (unsteadiness and difficulty coordinating movements), along with generalized tonic-clonic ("grand mal") seizures. Individuals with MEAK typically do not experience developmental delays.
Unverricht-Lundborg disease (Baltic myoclonus)
Myoclonus epilepsy and ragged red fibres (MERRF syndrome)
Lafora disease
Neuronal ceroid lipofuscinoses
Sialidosis
Dentatorubropallidoluysian atrophy (DRPLA)
Noninfantile neuronopathic form of Gaucher disease
Tetrahydrobiopterin deficiencies
Alpers disease
Juvenile Huntington disease
Niemann-Pick disease type C
North Sea progressive myoclonus epilepsy (NSPME)

Unverricht-Lundborg disease
This disease manifests between six and sixteen years and is most prevalent in Scandinavia and the Baltic countries. Myoclonus gradually becomes worse and less susceptible to medication. Cognitive decline is slow and sometimes mild. Patients typically do not live beyond middle-age, but there are exceptions. Phenytoin, an old and commonly used anticonvulsant, is known to seriously exacerbate the condition. It has autosomal recessive inheritance, and is caused by a mutation in the cystatin B (EPM1) gene on chromosome 21q22.3, which was discovered in 1996. It has been described as the least severe type of PME. Myoclonus epilepsy and ragged red fibres (MERRF syndrome)
Onset of this disease may be at any time and the severity and progression are varied. Tonic-clonic seizures and dementia are less apparent than with other forms of PME. The cause is a mitochondrial DNA mutation, so most familial cases are transmitted from the mother. A skeletal muscle biopsy will show ragged red fibres, hence the name. Lafora body disease
This disease typically begins between six and nineteen years after apparently normal development and generally results in death within ten years. It is characterised by the presence of Lafora bodies (polyglucosan inclusions) in neurons and other body tissue. The generalized seizures are usually well controlled by anticonvulsants, but the myoclonus soon proves refractory to treatment.