Test Details: Myoclonic Epilepsy Associated with Ragged Red Fibres (MERRF) is a rare inherited disorder characterised by myoclonus, generalized epilepsy, ataxia and ragged red fibers observed in histological sections of muscle biopsy tissue. The A8344G mutation in the tRNA Lys (MTTK) gene of mitochondria DNA accounts for about 80% of patients with typical clinical findings. Two additional mutations in the same gene, T8356C and G8363A, are present due to mitochondrial hetroplasmy. The heteroplasmy also underlies the phenotypic variability characteristics of mitochondrial diseases.