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MNGIE: from nuclear DNA to mitochondrial DNA
I Nishino1, A Spinazzola, M Hirano
1Department of Neurology, Columbia University, New York, NY 10032, USA. nishino@ncnp.go.jp
Neuromuscular Disorders : NMD
|February 13, 2001
Summary
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by thymidine phosphorylase gene mutations, leading to mitochondrial DNA alterations. This discovery classifies MNGIE as a nucleoside metabolism disorder, opening new research avenues.
Area of Science:
- Genetics
- Mitochondrial Biology
- Biochemistry
Background:
- Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare, severe autosomal recessive disorder.
- Clinical features include ptosis, ophthalmoparesis, gastrointestinal dysmotility, neuropathy, and leukoencephalopathy.
- Muscle biopsies show mitochondrial abnormalities and mtDNA alterations.
Purpose of the Study:
- To identify the genetic cause of MNGIE.
- To understand the molecular mechanisms underlying the disease.
- To establish a diagnostic marker for MNGIE.
Main Methods:
- Genetic linkage analysis to map the MNGIE locus to chromosome 22q13.32-qter.
- Gene sequencing to identify mutations in the thymidine phosphorylase (TP) gene.
- Spectrophotometric assay to measure TP enzymatic activity in patient leukocytes.
Main Results:
- Homozygous or compound-heterozygous mutations in the TP gene were identified in 35 MNGIE patients from diverse ethnic backgrounds.
- TP enzymatic activity was severely reduced in MNGIE patients, confirming loss-of-function mutations.
- Plasma thymidine levels were significantly elevated (over 20-fold) in MNGIE patients.
Conclusions:
- Loss-of-function mutations in the thymidine phosphorylase gene are the cause of MNGIE.
- MNGIE is classified as a disease of nucleoside dysmetabolism due to impaired thymidine catabolism.
- Elevated thymidine likely leads to mitochondrial DNA alterations via a salvage pathway.