Genes affected: mitochondrial DNA (MT-TK, MT-TF, MT-TL1, MT-TP)
Key clinical features of MERRF:
(1) myoclonus
(2) generalized epilepsy
(3) ataxia
(4) ragged-red fibers in a muscle biopsy
Additional clinical findings may include:
(1) sensorineural hearing loss
(2) myopathy
(3) peripheral neuropathy
(4) short stature
(5) dementia
(6) optic atrophy and/or ophthalmoparesis
(7) exercise intolerance
(8) cardiomyopathy with Wolff-Parkinson-White (WPW) syndrome
(9) pigmentary retinopathy
(10) pyramidal signs
(11) lipomatosis (multiple lipomas)
(12) respiratory insufficiency
Laboratory confirmation involves demonstration of a mitochondrial DNA pathologenic variant.
