MERRF
MERRF - Myoclonus Epilepsy With Ragged Red Fibers
Clinical Features
Patients with MERRF syndrome typically show myoclonic jerks, tonic-clonic seizures, mitochondrial myopathy, hearing loss, ataxia and dementia, but the severity of the phenotype is very variable. The occurrence of ragged red fibers is described in all forms of the disease.
Genetic Information
The most frequent cause of MERRF syndrome is the 8344A>G mutation in the mtDNA tRNA Lys gene. The MERRF phenotype can be also caused by other mtDNA mutations (ND5, other tRNA genes) and autosomal recessive mutations of the nuclear-encoded mitochondrial polymerase gamma (POLG1) gene. In cases with POLG1 mutations, multiple mtDNA deletions are usually present in muscle DNA.
Prevalence
The prevalence of the 8344 A>G mutation in Finnland is 0-1.5 : 100 000, in North-East England it was found to be 0 - 0.25 : 100 000.
Diagnostic
Indication
Method
1. Mutation analysis for 8344A>G in the mtDNA tRNA Lys gene by DNA sequencing
2. Southern blot / long-range PCR for mtDNA deletions
3. Mutation analysis of the entire coding and flanking intronic regions with intronic primers of the POLG1 gene by direct DNA sequencing
4. Mutation analysis for other mtDNA tRNA or ND5 mutations by DNA sequencing.
Sample Requirement
1, 3 and 4: 2 - 4 ml of EDTA-blood
2: muscle DNA
Duration
1, 2: 1 - 2 weeks
3, 4: 2 - 6 weeks
OMIM