Table 3

Progressive myoclonic epilepsies

InheritanceSeizure typeMyoclonusIntellectual disabilityCerebellar featuresAdditional clinical featuresDiagnosis
Unverricht-Lundborg disease
AR—CSTB gene.GTC and myoclonic epilepsy.Action myoclonus.Yes.Yes.Microcephaly, dystonic posturing and chorea in the limbs.Genetic test.
Lafora body disease (EPM2)AR—EPM2A or EPM2B gene.GTC and occipital seizures.Spontaneous myoclonus.Yes.No.Visual hallucinations and progressive neurological deterioration.Skin biopsy: Lafora bodies.
Genetic test.
Myoclonic epilepsy with ragged-red fibresMaternally inherited—mitochondrial DNA mutations (tRNALys gene).GTC.Yes.Yes.Ataxia, dementia, dystonia, parkinsonism, tremor and chorea.
Other findings: hearing loss, short stature, optic atrophy and cardiomyopathy.
Muscle biopsy: ragged-red fibres.
Genetic test.
Neuronal ceroid lipofuscinoses (NCL), also known as Batten disease.Lysosomal storage group of disorders.
AR or AD late-onset forms. PPT1, TPP1, CLN3, CLN5, CLN6, MFSD8, CLN8, CTSD, DNAJC5, CTSF, ATP13A2, GRN and KCTD7 genes.
GTC and myoclonic seizures leading to early death.Action myoclonus.Yes.No.Visual loss is frequently seen. In childhood, NCL is the most common lysosomal disorder. The adult type (Kuf’s disease) is the rarest of all the subtypes of NCL.Skin biopsy: curvilinear profiles, fingerprint profiles, granular osmophilic deposits.
Genetic test.
Dentatorubral-pallidoluysian atrophy (DRPLA)AD—expansion of CAG repeats in the DRPLA gene.Yes.Yes.Yes.Choreoathetosis, dementia and psychiatric symptoms. Patients with a PME phenotype have larger expansions (62–79 repeats) and earlier age of onset (<20 years old).Genetic test.
Sialidosis (type I)AR lysosomal storage disease caused by mutation in the NEU1 gene.Myoclonic epilepsy.Action myoclonus.Yes.Yes.Visual problems, hyper-reflexia, ataxia (second or the third decade of life). Type I is a milder variant and type II is a more severe variant with an earlier onset.Macular cherry-red spots may be seen but it is not pathognomonic.
Sialo-oligosaccharides in urine.
Genetic test.
  • AD, autosomal dominant; AR, autosomal recessive; CAG, cytosine–adenine–guanine; EPM1, progressive myoclonic epilepsy type 1; GTC, generalised tonic-clonic seizures; PME, progressive myoclonic epilepsy.