Identification of a Novel Variant in MT-CO3 Causing MELAS

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a maternally inherited mitochondrial disease. Most cases of MELAS are caused by the m.3243A > G variant in the MT-TL1 gene encoding tRNALeu(UUR). However, the genetic cause in 10% of patients with MELAS is unknown. We investigated the pathogenicity of the novel mtDNA variant m.9396G > A/MT-CO3 (p.E64K), which affects an extremely conserved amino acid in the CO3 subunit of mitochondrial respiratory chain (MRC) complex IV (CIV) in a patient with MELAS. Biochemical assays of a muscle biopsy confirmed remarkable CIV deficiency, and pathological examination showed ragged red fibers and generalized COX non-reactive muscle fibers. Transfer of the mutant mtDNA into cybrids impaired CIV assembly, followed by remarkable mitochondrial dysfunction and ROS production. Our findings highlight the pathogenicity of a novel m.9396G > A variant and extend the spectrum of pathogenic mtDNA variants.

Photosensitive Epilepsy and Polycystic Ovary Syndrome as Manifestations of MERRF

Objectives. Although endocrinologic involvement and epilepsy are frequent features of myoclonic epilepsy with ragged-red fibers (MERRF), polycystic ovary syndrome (PCOS) and photosensitive epilepsy have not been reported. Case Report. A 32-year-old female was diagnosed with MERRF at age 19 y upon presence of the four canonical features and the variant m.8344A > G in MT-TK (tRNA (Lys)) (blood heteroplasmy rate: 50%). She experienced recurrent photosensitive focal and generalised seizures since age 19 y, which could be triggered by flickering light or by looking at small stones, leaves, or dirty snow on the ground. Since the last 42 months, she was seizure-free upon levetiracetam (4000 mg/d), clonazepam (1.5 mg/d), and topiramate (25 mg/d). Additionally, she suffered from secondary amenorrhoea since adolescence. She was married between ages 19 y and 25 y but did not get pregnant. PCOS was diagnosed and treated with desogestrel plus estradiol. Nonetheless, the course was progressive, particularly with regard to ataxia, myocloni, and myopathy. Conclusions. The phenotypic spectrum of MERRF is broader than anticipated and may additionally include PCOS and photosensitive epilepsy. PCOS in MERRF may respond to hormone substitution and photosensitive epilepsy to levetiracetam, clonazepam, and topiramate.

Ganglionopathies Associated with MERRF Syndrome: An Original Report

Neuropathies in Myoclonic Epilepsy with Ragged Red Fibers (MERRF) syndrome are frequent but ganglionopathies have never been reported. We retrospectively identified 24 patients with MERRF mutations in the neuromuscular center Nord/Est/Ile de France (Pitié-Salpêtrière, Paris, France). Seventeen nerve conduction studies (NCS) were available. Five patients had MERRF syndrome and ganglionopathy, a pure sensory neuropathy. All of them displayed ataxia and mild clinical sensory abnormalities. Ganglionopathies have been reported in mitochondrial diseases but never in MERRF syndrome. We suggest that patients presenting with ganglionopathy, especially if associated with myopathy, lipomatosis or epilepsy, should be screened for MERRF mutations.