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Autosomal recessive
8%
9/120
Autosomal dominant
2%
3/120
X-linked dominant
10/120
X-linked recessive
12%
15/120
Mitochondrial inheritance
68%
82/120
Select Answer to see Preferred Response
This patient is experiencing myoclonus and the Gömöri trichrome stain (Figure A) of the muscle biopsy confirms the diagnosis of Myoclonic Epilepsy with Ragged Red Fibers (MERRF), which is a disease that is passed on via a mitochondrial inheritance pattern. MERRF is a mitochondrial disease that primarily affects the muscular and nervous systems. Due to heteroplasmy, the severity and symptoms vary between individuals and even among affected family members. The symptoms of MERRF are the following: myoclonus, myopathy, spasticity, epilepsy, ataxia, peripheral neuropathy, deterioration of cognitive function, as well as hearing and vision loss. Individuals with this disease are typically of short stature, have cardiomyopathy, and are prone to develop fatty tumors. DiMauro and Hirano review MERRF and the mutations that cause this syndrome. The gene most commonly affected is the MT-TK gene, which encodes for the tRNA-Lys; the specific mutation is a adenine to guanine substitution at position 8344, with 80% of affected individuals having this mutation. Due to heteroplasmy, various tissues may contain more or less mitochondria that have this mutation, therefore producing varying symptoms in individuals. DiMauro and Hirano also discuss the treatment of this disorder by stating that each symptom can be treated separately. Antiepileptic medications are given to control the seizures, and levetiractem, clonazepam, zonisamide, and valproic acid may be given for the myoclonus. Physical therapy and exercise is performed to help with the dysfunctional motor function. To treat the cardiomyopathy, pharmacologic therapy is also given depending on the patient's symptoms. Figure A demonstrates the red ragged fibers of MERRF. The affected mitochondria aggregate under the muscle plasma membrane; this affects the shape of the muscle fiber, causing it to be irregular and appear as red ragged fibers under the Gömöri trichrome stain. Illustration A demonstrates a normal Gömöri trichrome stain of a muscle biopsy. Notice the regular appearance of the muscle fibers versus the irregular, ragged appearance of the MERRF sample. Incorrect Answers: Answers 1-4: Myoclonic epilepsy with ragged red fibers is passed on via a mitochondrial inheritance pattern, not by these other choices.
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