reductase polymorphism, homocysteine and age

L. Todesco , C. Angst , P. Litynski , F. Loehrer , B. Fowler and W. E. Haefeli *Kantonsspital Basel, Switzerland, †University Children’s Hospital Basel, Switzerland, ‡University Hospital, Heidelberg, Germany

Abstract

Background Elevated fasting levels of total homocysteine are now accepted as an indepen- dent risk factor for the development of arteriosclerotic vascular diseases. A polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR), caused by the C677T point mutation, leads to increased thermolability of the enzyme, with reduced enzyme activity. We studied the frequency of this mutation in different groups of the Swiss adult population.

Patients and methods DNA from 361 subjects was screened for the thermolabile MTHFR variant with PCR. Included were healthy subjects without vascular disease (n¼ 118), older healthy subjects (n¼ 106), patients with coronary artery disease (CAD, n¼ 75), and patients with peripheral arterial occlusive disease (PAOD, n¼ 63).

Results In the different groups studied, homozygosity for the mutation ranged from 4·8 to 16·2%, with a frequency of 16·2% in the healthy cohort. The allele frequencies of the thermolabile allele were 38·5 and 27·3 in young and old controls, and 37·3 and 33·3 in CAD and PAOD patients. In the healthy younger subjects the mutant allele was 1·4 times more frequent compared to the older subjects (P¼ 0·01). No difference in either MTHFR genotype distribution (P¼ 0·33) or allele frequencies (P ¼ 0·48) between patients and controls was found. Except for the PAOD group with elevated tHcy levels for the þ/þ carriers compared to the other genotypes, no statistically significant difference was found comparing homocysteine levels with genotype.

Conclusion This study shows no link between the mutation and the occurrence of vascular disease but we found evidence pointing to a correlation between the mutation and longevity in our population.

Keywords Arteriosclerosis, homocysteine, methylenetetrahydrofolate reductase, mutation. Eur J Clin Invest 1999; 29 (12): 1003–1009

Introduction

as an independent risk factor for vascular disease in a large number of retrospective and some prospective studies [1,2].

Moderate increases of total homocysteine (tHcy) either fasting or post methionine loading have been established

The underlying cause for increased homocysteine (Hcy) levels in vascular disease patients and the exact mechanism by which Hcy induces vascular damage remain to be elucidated. Both genetic and nutritional factors such as folate [3], vitamin B12 [4] and B6 [5] certainly play a role; sometimes acting in combination.

Division of Clinical Pharmacology, Department of Internal Medicine, Kantonsspital Basel, Switzerland (L. Todesco); University Children’s Hospital Basel, Switzerland (C. Angst, P. Litynski, F. Loehrer, B. Fowler); Department of Internal Medicine VI, Clinical Pharmacology and University Hospital, Heidelberg, Germany (W. E. Haefeli).

Kang and coworkers [6] first showed a link between moderately disturbed function of MTHFR in lymphocytes, measured as an increased thermolability, and moderate increases of tHcy in plasma of coronary artery disease (CAD) patients. Following the cloning and sequencing of the gene for MTHFR [7], a C!T transition at 677, which results in an alanine to valine conversion at amino acid 222, was established as the cause of thermolability and mildly reduced specific activity of MTHFR [8]. Furthermore the

Received 15 March 1999; accepted 27 August 1999

patients with CAD with occlusions of 1–3 major coronary arteries undergoing percutaneous transluminal coronary angioplasty and 63 peripheral arterial occlusive disease (PAOD) patients. Six of these PAOD patients had inter- mittent claudication (Fontaine, stage II), and 59 suffered from critical limb ischemia (stage III/IV). Twenty-six patients had a history of one or more vascular events other than PAOD (in total 24 coronary artery and 5 cerebrovascular events). Subjects with a family history of premature vascular disease were excluded. After a fasting period of at least 4 h, blood samples were collected for the determination of tHcy, methyltetrahydrofolate (MeTHF), and MTHFR genotype.

presence of homozygosity for C677T was shown to result in slightly higher tHcy and this effect was amplified in subjects with total plasma folate levels below the median value [9].