ATHEROSCLEROSIS

Analysis of the apo E:apo C-I, angiotensin converting enzyme and methylenetetrahydrofolate reductase genes as candidates affecting

Daliah Galinsky a, Carolyn Tysoe a, Carol E. Brayne b, Douglas F. Easton b, A. Huppert c, Thomas R. Dening c, Eugene S. Paykel c, David C. Rubinsztein

b Institute of Public Health, Uni6ersity For6ie Site, Robinson Way, Cambridge, CB22SR, UK c Department of Psychiatry, Cambridge Uni6ersity, Addenbrooke’s Hospital, Hills Road, Cambridge, CB22QQ,

Received 10 June 1996; received in revised form 11 September 1996; accepted 11 November 1996

Abstract

Genetic factors are likely to affect human survival, since twin studies have shown greater concordance for age of death in monozygotic compared to dizygotic twins. Coronary artery disease is an important contributor to premature mortality in the UK. Accordingly, we have chosen genes associated with cardiovascular risk, apo E:apo C-I, angiotensin converting enzyme (ACE) and methylenetetrahydrofolate reductase (MTHFR), as candidates which may affect longevity:survival into old age. An association study was performed by comparing allele and genotype frequencies at polymorphic loci associated with these genes in 182 women and 100 men aged 84 years and older with 100 boys and 100 girls younger than 17 years. MTHFR allele and genotype frequencies were similar in the elderly and young populations. Apo C-I allele and genotype frequencies were significantly different in the elderly women compared to the younger sample (PB0.05). No difference was observed in the elderly men. At the neighbouring apo E gene, we only observed a difference between genotypes in the elderly women and the young sample; however, this did not retain significance when the genotype frequencies of the young sample were adjusted to values expected from the allele frequencies on the basis of Hardy-Weinberg equilibrium and compared to observed genotypes in elderly men and women. In contrast to previous studies, apo E2 was not overrepresented in the elderly men or women. Thus, the proposition that apo E2, E3 and E4 protein isoforms are themselves functionally associated with increasing risks for early death, may be too simplistic. The I:I ACE was depleted in the elderly males but not the elderly females. Furthermore, significant differences were observed between ACE genotypes in elderly men and elderly women. These data suggest that the penetrance of loci which influence survival may vary according to sex. The depletion of the ACE I:I genotype in elderly men is generally consistent with a previous study which found decreased frequencies of the I allele in French centenarians compared to younger controls. However, these results are apparently paradoxical, since others have suggested that the I allele is associated with increased cardiovascular risk. Clarification of the overall effect of a genotype on survival will be vital if therapies are to be considered which target specific genetic variants. © 1997 Elsevier Science Ireland Ltd.

Keywords: Longevity; Ageing; Apo E; Apo C-I; Angiotensin converting enzyme; Methylenetetrahydrofolate reductase

1. Introduction

Premature mortality is generally regarded as mortal- ity below the age of 65. The main causes of death in the UK in individuals below this age and for the two

succeeding decades are cardiovascular diseases and can- cers. The greatest recent change in the UK demography has been in the number of people aged 84 and over. It is important to understand the genetic influences on survival in order to predict better the likely configura- tions of health and disability in the future and to prevent chronic disease.

ble for the apo E association with this disease, we were interested in investigating the suggestions of Chartier- Harlin [9] and Templeton [8] that the apo C-I locus, either by itself or in combination with the apo E locus, could provide more information than apo E alone in association studies.

(MTHFR) gene was examined as a candidate in this study, since MTHFR catalyses the reduction of 5,10- methylenetetrahydrofolate to 5-methylenetetrahydrofo- late, the principal form of folate present in the circulation, which acts as a carbon donor for remethy- lation of homocysteine to methionine. Autosomal reces- sive MTHFR deficiency is characterised by homocysteinaemia and patients are at increased risk for arteriosclerosis and thrombosis [10]. Recently, Frosst et al. [11] have described a common C to T substitution at nucleotide 677 in this gene which results in the conver- sion of alanine to valine. Homozygotes for this muta- tion, which is associated with thermolability of the enzyme, are at increased risk for cardiovascular disease.

Genetic factors are likely to affect human survival, since twin studies have shown greater concordance for age of death in monozygotic compared to dizygotic twins [1]. Although many of these genetic influences affect specific diseases which are important contributors to premature mortality, like cardiovascular disease, it is possible that the biological effects of genetic variables are not confined simply to single pathological processes. When attempting to look at genes for complex diseases, there is no reason to assume that one gene impacts on only one disease. For instance, apo E allelic variation is associated with coronary artery disease and Alzheimer’s disease risk (reviewed in [2]) and there are suggestions that allelic variants which predispose to certain diseases may be associated with lower risks for other diseases [3].

In this study, we have compared allele and genotype frequencies at polymorphic loci associated with these candidate genes in a group of individuals aged 84 and older from Cambridge, UK. and a regionally-matched young population aged 17 years or less. This strategy is similar to that used by the previous studies which have investigated genes associated with longevity [3–5].