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Defects in human methionine synthase in cblG patients
1Biochemistry Department, University of Nebraska, Lincoln 68588-0664, USA.
Human Molecular Genetics
|December 1, 1996
Summary
Inborn errors of methionine synthase (cblG) can stem from reduced enzyme levels or impaired activation. This study identifies mutations in the methionine synthase gene as the cause of the cblG phenotype, linking it to elevated homocysteine.
Area of Science:
- Biochemistry
- Genetics
- Molecular Biology
Background:
- Inborn errors of methionine synthase (MS) are classified into cblG and cblE complementation groups.
- Understanding the molecular basis of MS deficiency is crucial for diagnosing and treating associated health issues.
Purpose of the Study:
- To investigate the molecular basis of the cblG phenotype in patients with isolated functional methionine synthase deficiency.
- To identify specific mutations in the methionine synthase gene responsible for impaired enzyme activity.
Main Methods:
- Biochemical assays to assess methionine synthase activity and enzyme levels.
- Northern analysis to evaluate mRNA levels.
- Mutation detection through sequencing of the methionine synthase gene.
Main Results:
- One cblG patient exhibited significantly reduced methionine synthase mRNA levels, indicating a transcriptional or message stability issue.
- A second cblG patient harbored compound heterozygous mutations in the methionine synthase gene, affecting the reductive activation cycle.
- Specific mutations identified were Pro1173Leu and an isoleucine deletion at residue 881, impacting AdoMet-binding and B12-binding domains, respectively.
Conclusions:
- This study provides the first direct evidence linking mutations in the methionine synthase gene to the cblG phenotype.
- The findings highlight the role of methionine synthase gene mutations in causing elevated homocysteine levels.
- Elevated homocysteine is implicated in serious health conditions, including neural tube defects and cardiovascular diseases.