Leigh-like syndrome with the T8993G mutation in the mitochondrial ATPase 6 gene: long-term follow-up discloses a slowly progressive course

A meta-analysis and systematic review of Leigh syndrome: clinical manifestations, respiratory chain enzyme complex deficiency, and gene mutations

Leigh syndrome (also called Leigh disease or subacute necrotizing encephalomyelopathy) is a rare inherited neurometabolic disorder, which affects the central nervous system. This meta-study systematically analyzed clinical manifestations, respiratory chain enzyme complex deficiency, and gene mutations.Literature was searched for publications in MEDLINE, EMBASE, and the China National Knowledge Infrastructure database for meta-analyses of the incidence of clinical symptoms, laboratory assessments, imaging data, muscle biopsy histochemical staining, activity of the mitochondrial respiratory chain enzyme complex, gene mutations, and the association between age at disease onset and type of gene mutations.This study included 5 studies with 385 Leigh syndrome patients. The most common clinical features of Leigh syndrome included elevated blood and/or cerebrospinal fluid (CSF) levels of lactate (72%), developmental retardation (57%), hypotonia (42%), followed by respiratory dysfunction (34%), epileptic seizures (33%), poor feeding (29%), and weakness (27%). Approximately 80% of the patients had deficiencies of the respiratory chain enzyme complex or isolated complex I deficiency (35%), 32% had mitochondrial DNA (mtDNA) mutations, and 38% had nuclear DNA (nDNA) mutations. Patients with nDNA mutations were younger than those with mtDNA mutations (8.82 ± 13.88 vs 26.20 ± 41.11 years, P = .007).The data from the current meta-analysis demonstrated a variety of clinical and molecular manifestations of Leigh syndrome, with upregulated lactate levels in the blood or CSF being the most common feature. Diagnosis of Leigh syndrome could be confirmed using combined enzymatic and genetic analyses.

Frequency and association of mitochondrial genetic variants with neurological disorders

Mitochondria are small cytosolic organelles and the main source of energy production for the cells, especially in the brain. This organelle has its own genome, the mitochondrial DNA (mtDNA), and genetic variants in this molecule can alter the normal energy metabolism in the brain, contributing to the development of a wide assortment of Neurological Disorders (ND), including neurodevelopmental syndromes, neurodegenerative diseases and neuropsychiatric disorders. These ND are comprised by a heterogeneous group of syndromes and diseases that encompass different cognitive phenotypes and behavioral disorders, such as autism, Asperger's syndrome, pervasive developmental disorder, attention deficit hyperactivity disorder, Huntington disease, Leigh Syndrome and bipolar disorder. In this work we carried out a Systematic Literature Review (SLR) to identify and describe the mitochondrial genetic variants associated with the occurrence of ND. Most of genetic variants found in mtDNA were associated with Single Nucleotide Polimorphisms (SNPs), ~79%, with ~15% corresponding to deletions, ~3% to Copy Number Variations (CNVs), ~2% to insertions and another 1% included mtDNA replication problems and genetic rearrangements. We also found that most of the variants were associated with coding regions of mitochondrial proteins but were also found in regulatory transcripts (tRNA and rRNA) and in the D-Loop replication region of the mtDNA. After analysis of mtDNA deletions and CNV, none of them occur in the D-Loop region. This SLR shows that all transcribed mtDNA molecules have mutations correlated with ND. Finally, we describe that all mtDNA variants found were associated with deterioration of cognitive (dementia) and intellectual functions, learning disabilities, developmental delays, and personality and behavior problems.

Leigh Syndrome in Childhood: Neurologic Progression and Functional Outcome

Background and Purpose

Few studies have analyzed the clinical course and functional outcome in Leigh syndrome (LS). The aim of this study was to determine the clinical, radiological, biochemical, and genetic features of patients with LS, and identify prognostic indicators of the disease progression and neurological outcome.

Methods

Thirty-nine patients who had been diagnosed with LS at the Seoul National University Children's Hospital were included. Their medical records, neuroimaging findings, and histological/biochemical findings of skeletal muscle specimens were reviewed. Targeted sequencing of mitochondrial DNA was performed based on mitochondrial respiratory chain (MRC) enzyme defects.

Results

Isolated complex I deficiency was the most frequently observed MRC defect (in 42% of 38 investigated patients). Mitochondrial DNA mutations were identified in 11 patients, of which 81.8% were MT-ND genes. The clinical outcome varied widely, from independent daily activity to severe disability. Poor functional outcomes and neurological deterioration were significantly associated with early onset (before an age of 1 year) and the presence of other lesions additional to basal ganglia involvement in the initial neuroimaging.

Conclusions

The neurological severity and outcome of LS may vary widely and be better than those predicted based on previous studies. We suggest that age at onset and initial neuroimaging findings are prognostic indicators in LS.

NARP Syndrome: A 20-Year Follow-Up

One member of a pedigree with NARP syndrome (neurogenic weakness, ataxia, and retinitis pigmentosa), a mitochondrial disorder due to a point mutation at position 8993 in the mitochondrial genome ATPase 6 gene, was reevaluated some 20 years after first being reported in the medical literature. Initially assessed at age 39 years, she had retinitis pigmentosa and a mild sensory axonal neuropathy, typical features of NARP, but was otherwise clinically normal. At age 59 years, she was registered blind, had sensorineural hearing impairment, had recently been diagnosed with diabetes mellitus, and may have had some mild cognitive impairment. This case shows that the clinical phenotype of NARP due to mitochondrial dysfunction may evolve over a period of decades.