Dichloroacetate therapy in Leigh syndrome with a mitochondrial T8993C mutation

Targeted Therapies for Leigh Syndrome: Systematic Review and Steps Towards a 'Treatabolome'

BACKGROUND

Leigh syndrome (LS) is the most frequent paediatric clinical presentation of mitochondrial disease. The clinical phenotype of LS is highly heterogeneous. Though historically the treatment for LS is largely supportive, new treatments are on the horizon. Due to the rarity of LS, large-scale interventional studies are scarce, limiting dissemination of information of therapeutic options to the wider scientific and clinical community.

OBJECTIVE

We conducted a systematic review of pharmacological therapies of LS following the guidelines for FAIR-compliant datasets.

METHODS

We searched for interventional studies within Clincialtrials.gov and European Clinical trials databases. Randomised controlled trials, observational studies, case reports and case series formed part of a wider MEDLINE search.

RESULTS

Of the 1,193 studies initially identified, 157 met our inclusion criteria, of which 104 were carried over into our final analysis. Treatments for LS included very few interventional trials using EPI-743 and cysteamine bitartrate. Wider literature searches identified case series and reports of treatments repleting glutathione stores, reduction of oxidative stress and restoration of oxidative phosphorylation.

CONCLUSIONS

Though interventional randomised controlled trials have begun for LS, the majority of evidence remains in case reports and case series for a number of treatable genes, encoding cofactors or transporter proteins of the mitochondria. Our findings will form part of the international expert-led Solve-RD efforts to assist clinicians initiating treatments in patients with treatable variants of LS.

Long-term outcome of Leigh syndrome caused by the NARP-T8993C mtDNA mutation

Mutations at mitochondrial DNA (mtDNA) nucleotide 8993 can cause neurogenic weakness, ataxia and retinitis pigmentosa (NARP syndrome), or maternally inherited Leigh syndrome (LS), with a correlation between the amount of mutant mtDNA and the severity of the neurological disease. The T8993C mutation is generally considered to be clinically milder than the T8993G mutation but when the level of heteroplasmy exceeds 90%, progressive neurodegeneration has been found. We report on a long-term follow-up of a patient who presented at 4 years of age with typical LS but showed an unexpected resolution of his symptoms and a favorable outcome. At 18 years of age, his neurological examination was near normal, with neither peripheral neuropathy nor retinopathy. mtDNA analysis identified the presence of T8993C mutation at high level (>95%) in the patient's blood leukocytes. This case report and literature review emphasizes the variability of the phenotypic expression of the T8993C mutation and the need for caution in predictive counseling in such patients. (c) 2007 Wiley-Liss, Inc.

Central nervous system manifestations of mitochondrial disorders

The central nervous system (CNS) is, after the peripheral nervous system, the second most frequently affected organ in mitochondrial disorders (MCDs). CNS involvement in MCDs is clinically heterogeneous, manifesting as epilepsy, stroke-like episodes, migraine, ataxia, spasticity, extrapyramidal abnormalities, bulbar dysfunction, psychiatric abnormalities, neuropsychological deficits, or hypophysial abnormalities. CNS involvement is found in syndromic and non-syndromic MCDs. Syndromic MCDs with CNS involvement include mitochondrial encephalomyopathy, lactacidosis, stroke-like episodes syndrome, myoclonic epilepsy and ragged red fibers syndrome, mitochondrial neuro-gastrointestinal encephalomyopathy syndrome, neurogenic muscle weakness, ataxia, and retinitis pigmentosa syndrome, mitochondrial depletion syndrome, Kearns-Sayre syndrome, and Leigh syndrome, Leber's hereditary optic neuropathy, Friedreich's ataxia, and multiple systemic lipomatosis. As CNS involvement is often subclinical, the CNS including the spinal cord should be investigated even in the absence of overt clinical CNS manifestations. CNS investigations comprise the history, clinical neurological examination, neuropsychological tests, electroencephalogram, cerebral computed tomography scan, and magnetic resonance imaging. A spinal tap is indicated if there is episodic or permanent impaired consciousness or in case of cognitive decline. More sophisticated methods are required if the CNS is solely affected. Treatment of CNS manifestations in MCDs is symptomatic and focused on epilepsy, headache, lactacidosis, impaired consciousness, confusion, spasticity, extrapyramidal abnormalities, or depression. Valproate, carbamazepine, corticosteroids, acetyl salicylic acid, local and volatile anesthetics should be applied with caution. Avoiding certain drugs is often more beneficial than application of established, apparently indicated drugs.