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ORIGINAL INVESTIGATION: De Benedictis, E. Falcone, G. Rose, R. Ruffolo, Spadafora, G. Baggio, S. Bertolini, D. Mari, Mattace, D. Monti, M. Morellini, P. Sansoni, and Franceschi.

DNA multiallelic systems reveal gene/longevity associations not detected by diallelic systems: The APOB locus.

Received: 27 November 1995 / Revised: 24 July 1996

Abstract:
To identify possible genetic factors affecting human longevity, we compared allele pools at two candidate loci for longevity between a sample of 143 centenarians (S) and a control sample of 158 individuals (C). The candidate loci were APOB and TPO, which code for apolipoprotein B and thyroid peroxidase, respectively. Both restriction fragment length (RFL) (XbaI and EcoRI) 2488 4154 and variable number of tandem repeat (VNTR) (3 APOB-VNTR) polymorphisms were analyzed at the APOB locus; the TPO-VNTR polymorphism (intron 10) was analyzed at the TPO locus. The main result of the investigation was that there is an association between the APOB locus and longevity that is revealed only when multiallelic polymorphisms are considered. In particular: (i) the frequency of 3 APOB-VNTR alleles with fewer than 35 repeats is significantly lower in cases than in controls; (ii) the linkage disequilibrium between the XbaI-RFLP and the EcoRI-RFLP is significantly different from 0 in cases but not in controls; (iii) the EcoRI-RFLP and XbaI-RFLP allele frequencies do not discriminate between cases and controls. The differences observed between case and control allele pools are specific to the APOB locus, since no significant difference was observed at the TPO locus.

Introduction:
Longevity can be regarded as a multifactorial trait, resulting from the interaction between environmental factors and sets of epistatic alleles having pleiotropic age-dependent effects (Kirkwood and Franceschi 1992). A possible approach to the identification of these longevity alleles is the comparative analysis of polymorphic markers at candidate loci between a long-lived group and a control group (Schachter et al. 1993). Indeed, it is expected that if a certain gene affects lifespan, there will be a difference between the allele pools of the long-lived and the control groups. So far, significant longevity/allele associations have been found at the HLA (Proust et al. 1982; Takata et al. 1987), ACE (Schachter et al. 1994), APOB (Kervinen et al. 1994), APOE (Kervinen et al. 1994; Louhija et al. 1994; Schachter et al. 1994), and APOC (Louhija et al. 1994) loci.

P. Spadafora: Department of Cell Biology, University of Calabria, Rende, Italy. G. Baggio: Institute of Internal Medicine, University of Padua, Padua, Italy. S. Bertolini: Atherosclerosis Prevention Centre, Department of Internal Medicine, University of Genoa, Genoa, Italy. D. Mari: Hemophilia and Thrombosis Centre, University of Milan, Milan, Italy. R. Mattace: Chair of Geriatrics, University of Reggio Calabria, Catanzaro, Italy. D. Monti: Department of Biomedical Sciences, University of Modena, Modena, Italy. M. Morellini: Department of Experimental Medicine and Pathology, University La Sapienza, Rome, Italy. P. Sansoni: Institute of Clinical Medical Genetics and Medical Therapy, University of Parma, Parma, Italy.

The information content of a genetic marker is a function of the number and the relative frequencies of different alleles found at that locus in a population (Botstein et al. 1980). DNA markers resulting from a variable number of tandem repeats (VNTR) are highly informative multiallelic systems (Harding 1992) that can be analyzed by polymerase chain reaction (PCR) amplification of the variable region. Because of their high information content, VNTR markers at candidate loci could be more efficient than single diallelic polymorphisms in revealing gene/longevity associations.