Biochemical-clinical correlation in patients with different loads of the mitochondrial DNA T8993G mutation.

TitleBiochemical-clinical correlation in patients with different loads of the mitochondrial DNA T8993G mutation.
Publication TypeJournal Article
Year of Publication2002
AuthorsCarelli, V, Baracca, A, Barogi, S, Pallotti, F, Valentino, MLucia, Montagna, P, Zeviani, M, Pini, A, Lenaz, G, Baruzzi, A, Solaini, G
JournalArch Neurol
Volume59
Issue2
Pagination264-70
Date Published2002 Feb
ISSN0003-9942
KeywordsAdenosine Triphosphate, Ataxia, Blood Platelets, DNA Mutational Analysis, DNA, Mitochondrial, Female, Gene Expression Regulation, Humans, Hydrolysis, Leigh Disease, Male, Nervous System Diseases, Phenotype, Retinitis Pigmentosa
Abstract

OBJECTIVE: To investigate the correlation between biochemical and clinical phenotype in 6 patients from 3 unrelated families with different mutation loads (heteroplasmy) of the T8993G mitochondrial DNA mutation associated with neuropathy, ataxia, and retinitis pigmentosa-Leigh syndrome.METHODS: We studied adenosine triphosphate (ATP) synthase activity (synthesis and hydrolysis) in platelet-derived submitochondrial particles and assessed mutant loads both in platelets used for biochemical analysis and in other available tissues. Biochemical and molecular results were correlated with clinical features.RESULTS: The rate of ATP hydrolysis was normal, but ATP synthesis was severely impaired (30% to 4% of residual activity) in patients harboring 34% to 90% mutant mitochondrial DNA, without any evidence of a threshold for the expression of this defect. There was little variation in heteroplasmy among tissues from each patient, but wider variability was detected in 2 mothers. Correlation of heteroplasmy and clinical and biochemical features suggested that ATP synthesis is defective at mutant loads as low as 34% and is extremely reduced at mutant loads above 80% when the phenotype is neuropathy, ataxia, and retinitis pigmentosa-Leigh syndrome.CONCLUSIONS: This study indicates a close relationship between tissue heteroplasmy, expression of the biochemical defect in platelets, and clinical involvement. The biochemical defect was greater than previously reported, and we found no evidence of a biochemical threshold. The uniform distribution of high mutant loads among our patients' tissues suggests a differential tissue-specific reliance on mitochondrial ATP synthesis.

Alternate JournalArch. Neurol.
Citation Key1350
PubMed ID11843698