Review Question - QID 106504

Mitochondrial diseases such as myoclonic epilepsy with ragged red fibers (MERRF) demonstrate a maternal inheritance pattern.

Myoclonic epilepsy with ragged red fibers is an extremely rare mitochondrial disease with an estimated prevalence of approximately 1/400,000. It presents with myoclonic seizures and neurologic deficits. It is caused by a point mutation in mitochondrial DNA which disrupts the synthesis of proteins necessary for oxidative phosphorylation. Because all mitochondria are inherited from an offspring's mother, mitochondrial diseases such as MERRF demonstrate a maternal or mitochondrial pattern of inheritance with every offspring of the mother having the disease. However to heteroplasmy, the random divide of mitochondria, these disease express strong degrees of variable expression between generations and siblings.

Lorenzoni et al. review the clinical and laboratory manifestations, brain images, electrophysiological patterns, histology, and molecular findings in MERFF. To diagnose they state that diagnostic criteria for MERRF include typical manifestations of the disease: myoclonus, generalized epilepsy, cerebellar ataxia, and ragged red fibers (RRF) on muscle biopsy.

Khurana et al. review the relationship between mitochondrial dysfunction and epilepsy. They state that because neurons are terminally differentiated cells that lack significant regenerative capacity and have a high energy demand, they are more vulnerable to mitochondrial dysfunction and thus epilepsy is often a manifestation of mitochondrial dysfunction.

Figure F demonstrates a biopsy with the characteristic red ragged fibers of MERRF.

Incorrect Answers:
Answer 1: This pedigree demonstrates an autosomal dominant mode of inheritance.
Answer 3: This pedigree demonstrates an autosomal recessive mode of inheritance.
Answer 4: This pedigree demonstrates an X-linked dominant mode of inheritance.
Answer 5: This pedigree demonstrates an X-linked recessive mode of inheritance.