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.
The symptoms are progressive, and individuals with MEAK often need to use a wheelchair by their late teenage years because of movement difficulties and myoclonus. Many individuals with MEAK report temporary improvement of symptoms when they have a high fever. Seizures may become less frequent in adulthood, but other neurological complications, including myoclonus, ataxia and tremor, may worsen. Myoclonic epilepsy and ataxia due to potassium (K+) channel mutation (MEAK) is caused by a specific pathogenic variant ("mutation") in KCNC1 (c. 959G>A; p.Arg320His). KCNC1-related developmental and epileptic encephalopathy is associated with other pathogenic variants in KCNC1. In most individuals with KCNC1-related disorders, the pathogenic KCNC1 variant occurred spontaneously (de novo) and was not inherited from either parent. Epidemiology
PME accounts for less than 1% of epilepsy cases at specialist centres. The incidence and prevalence of PME is unknown, but there are considerable geography and ethnic variations amongst the specific genetic disorders. One cause, Unverricht Lundborg Disease, has an incidence of at least 1:20,000 in Finland. See also
Juvenile myoclonic epilepsy
Spinal muscular atrophy with progressive myoclonic epilepsy

References
External links

GeneReview/NCBI/NIH/UW entry on Progressive Myoclonus Epilepsy with Ataxia