General description

Myoclonic epilepsy with ragged-red fibers (MERRF) is a rare mitochondrial disorder that typically manifests in adolescence or early adulthood, though it can also appear in childhood after normal development. It affects multiple body systems, primarily the nervous system and skeletal muscles. The hallmark symptom is myoclonus—sudden, brief muscle jerks that may involve the limbs or entire body. Other common symptoms include seizures, cerebellar ataxia, muscle weakness, exercise intolerance, cognitive decline, short stature, optic atrophy, hearing loss, cardiomyopathy, and peripheral neuropathy.

MERRF is caused by mutations in mitochondrial DNA (mtDNA), most commonly the A8344G mutation, with A3243G also implicated. These mutations are heteroplasmic, meaning both normal and mutant mtDNA coexist in the same individual, leading to variability in the onset age and symptoms. Ragged red fibers (RRF), indicative of mitochondrial abnormalities, are present in muscle biopsies and are not unique to MERRF, as they can appear in other mitochondrial myopathies. The disorder is maternally inherited due to the nature of mtDNA transmission.

References

1. Ito, S., et al. "Clinical and brain MR imaging features focusing on the brain stem and cerebellum in patients with myoclonic epilepsy with ragged-red fibers due to mitochondrial A8344G mutation." American journal of neuroradiology 29.2 (2008): 392-395.