Mechanisms of Ageing and Development 127 (2006) 597–599

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A longitudinal study of the effect of GSTT1 and GSTM1 gene copy number on survival

, C. Brasch-Andersen , L. Bathum , T.A. Kruse , K. Christensen

aDepartment of Epidemiology, Institute of Public Health, University of Southern Denmark, Denmark bDepartment of Biochemistry, Pharmacology and Genetics, Odense University Hospital, Sdr. Boulevard 29, 5000 Odense C, Denmark Received 21 December 2005; received in revised form 10 February 2006; accepted 23 February 2006

Abstract

Deletions of the glutathione S-transferase superfamily genes GSTT1 and GSTM1 has been associated with oxidative stress related diseases and recently explored as factors implicated in longevity as well. Reported results have been conflicting, which may partially be caused by the traditional use of assays unable to discriminate between carriers of one or two functional genes.

Using a quantitative realtime PCR method facilitating quantification of gene copy number, we evaluated the influence of GSTT1 and GSTM1 gene deletions on longevity in a longitudinal study of 681 elderly Danish twins. The mean follow-up time was 7.6 years and during this time a total of 294 deaths occurred. The results demonstrated a non-significant trend for carriage of two copies of the GSTM1 functional gene to be a protective factor, whereas both heterozygosity and homozygosity for the GSTT1 functional gene was associated with a moderate but significant increased mortality in women (hazard rate 2.46 (CI : 1.43–4.23) and 2.22 (CI : 1.25–3.94) for one and two alleles, respectively). To our knowledge, this is 95 95 the first longitudinal study exploring the influence of GST gene polymorphisms on longevity and these data implies that GST gene copy numbers do affect mortality risk in the elderly.

Keywords: Glutathione S-transferase; Polymorphisms; Quantitative PCR; Ageing; Longevity

The GSTT1 and GSTM1 genes are members of the glutathione S-transferase (GST) superfamily, comprising genes that encodes a variety of enzymes involved in protection against harmful exogenous substances, such as carcinogens and other xenobiotics, as well as endogenously produced reactive oxygen species (Hayes et al., 2005). Common polymorphisms consisting in deletion of the entire gene has been described for both GSTT1 and GSTM1 leading to a complete lack of activity, and the deletion of one or two alleles (null genotype) has been associated with an increased risk of various types of cancer (Alexandrie et al., 2004; Ates et al., 2005; Rajagopal et al., 2005), asthma and other respiratory diseases (Brasch- Andersen et al., 2004; Tamer et al., 2004).

Muiras et al. (1998) thus found no association between homozygosity for GSTM1 deletions and longevity when comparing 565 French centenarians and 229 younger controls. In a later study using Italian centenarians compared to control subjects of younger age this lack of association was confirmed by Taioli et al. (2001), who on the other hand found a significant increase in the prevalence of GSTT1 deletions in the centenarians.

Soon after, Yamamura et al. (2001) found a decreased frequency of the GSTM1 null genotype in Japanese centenar- ians compared to a younger control group, whereas there was no difference in the prevalence of the GSTT1 null genotype. Conversely, Pesch et al. (2004) recently reported a non- significant trend of GSTT1 deletions being slightly less frequent, and GSTM1 deletions marginally more frequent in 205 German octogenarians compared to a reference group of 294 persons aged less than 80 years old.

As mediators of protection against oxidative stress the GSTT1 and GSTM1 genes serve as excellent candidates for studies of successful ageing and longevity. Accordingly, several recent studies have investigated the influence of the presence/

Two obvious explanations may in part account for these discrepancies. First, all four studies use a cross sectional design,

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Adjusting for other relevant covariates, such as smoking status, current or previous pulmonary or cancer diseases, as well as other age-related diseases had virtually no effect on the hazard rate estimates.

an approach that could potentially pose a problem since cohort specific characteristics may confound the comparison between the centenarians and younger cohorts. Second, none of these studies discriminated between genotypes with one and two copies of GSTM1 and GSTT1, which probably reduces the power to observe an effect of the polymorphisms and furthermore precludes distinction between the various genetic models.

The suggested protective effect of inheriting two functional GSTM1 genes emphasises the importance of distinguishing between heterozygote and homozygote GSTM1 gene carriers, and may thus explain the lack of association found in previous studies. These results could be explained by a genetic mechanism with a dominantly acting harmful effect of the gene deletion. This contrasts with the general expectation that a deleterious effect of a gene deletion would follow either a recessive or an additive mechanism. However, these are only suggestive results which should obviously be interpreted with caution.