Myoclonic epilepsy with ragged red fibres

Myoclonic Epilepsy with Ragged Red Fibres

Myoclonic Epilepsy with Ragged Red Fibres (MERRF) is a rare mitochondrial disorder characterized by a combination of myoclonus, generalized epilepsy, ataxia, muscle weakness, and the presence of ragged red fibers in muscle biopsy. It is one of the mitochondrial encephalomyopathies, a group of disorders caused by defects in the mitochondrial DNA (mtDNA).

Clinical Features

MERRF typically presents in childhood or adolescence, although the age of onset can vary. The hallmark features of MERRF include:

• Myoclonus: Sudden, involuntary muscle jerks that are often the first symptom.
• Generalized Epilepsy: Seizures that can be difficult to control.
• Ataxia: Loss of coordination and balance.
• Muscle Weakness: Progressive weakness, particularly in the proximal muscles.
• Ragged Red Fibres: Abnormal muscle fibers that appear ragged and red when stained and viewed under a microscope.

Other symptoms may include hearing loss, short stature, optic atrophy, and cardiomyopathy.

Pathophysiology

MERRF is caused by mutations in the mitochondrial DNA, most commonly in the MT-TK gene, which encodes for mitochondrial tRNA for lysine. These mutations impair mitochondrial protein synthesis, leading to defective oxidative phosphorylation and reduced ATP production. The accumulation of defective mitochondria in muscle cells leads to the characteristic ragged red fibers.

Diagnosis

Diagnosis of MERRF is based on clinical features, family history, and laboratory tests. Key diagnostic steps include:

• Muscle Biopsy: Demonstrates ragged red fibers.
• Genetic Testing: Identifies mutations in the mitochondrial DNA, particularly in the MT-TK gene.
• Lactate Levels: Elevated lactate levels in blood or cerebrospinal fluid can support the diagnosis.

Treatment

There is currently no cure for MERRF. Treatment is symptomatic and supportive, focusing on managing seizures, myoclonus, and other symptoms. Antiepileptic drugs, physical therapy, and occupational therapy are commonly used.

Prognosis

The prognosis for individuals with MERRF varies. The disease is progressive, and the severity of symptoms can differ widely among affected individuals, even within the same family. Early diagnosis and management can improve quality of life.

Also see

• Mitochondrial disease
• Epilepsy
• Ataxia
• Muscle biopsy