Inheritance | Seizure type | Myoclonus | Intellectual disability | Cerebellar features | Additional clinical features | Diagnosis | |
Unverricht-Lundborg disease (EPM1) | 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 fibres | Maternally 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.