Haplotype-based identification of a microsomal transfer protein marker associated with the human lifespan

Bard J. Geesaman*, Erica Benson*, Stephanie J. Brewster*, Louis M. Kunkel†, He´le`ne Blanche´‡, Gilles Thomas‡, Thomas T. Perls§, Mark J. Daly¶, and Annibale A. Puca*(cid:1)

*Elixir Pharmaceuticals, Cambridge, MA 02139; †Howard Hughes Medical Institute, Genetics Division, Children’s Hospital and Harvard Medical School, Boston, MA 02215; ‡Foundation Jean Dausset–Centre d’E´tude du Polymorphisme Humain, 27 Rue Juliette Dodu, 75010 Paris, France; §Geriatrics Section, Boston Medical Center and Boston University School of Medicine, Boston, MA 02118; and ¶Whitehead Institute for Biomedical Research and Whitehead(cid:2)Massachusetts Institute of Technology Center for Genome Research, 9 Cambridge Center, Cambridge, MA 02139

Contributed by Louis M. Kunkel, September 29, 2003

LLI from the U.S. A follow-up study investigating LLI from France also demonstrated statistical distortion at MTP, but did not completely confirm the observations from the U.S. cohort.

We previously reported a genomewide linkage study for human longevity using 308 long-lived individuals (LLI) (centenarians or near-centenarians) in 137 sibships and identified statistically sig- nificant linkage within chromosome 4 near microsatellite D4S1564. This interval spans 12 million bp and contains (cid:1)50 putative genes. To identify the specific gene and gene variants impacting lifespan, we performed a haplotype-based fine-mapping study of the in- terval. The resulting genetic association study identified a haplo- type marker within microsomal transfer protein as a modifier of human lifespan. This same variant was tested in a second cohort of LLI from France, and although the association was not replicated, there was evidence for statistical distortion in the form of Hardy– Weinberg disequilibrium. Microsomal transfer protein has been identified as the rate-limiting step in lipoprotein synthesis and may affect longevity by subtly modulating this pathway. This study provides proof of concept for the feasibility of using the genomes of LLI to identify genes impacting longevity.

Methods

Ascertainment and Phenotyping. U.S.cohort.The study sam-

ple consists of 653 individuals (197 males and 456 females) 98 years and older (mean 100.8) recruited through Elixir Pharma- ceuticals, Beth Israel Deaconess Medical Center, Children’s Hospital of Boston, and the New England Centenarian Study previously of Beth Israel Deaconess Medical Center and now of Boston University Medical Center. Individuals were identified and recruited by a variety of methods including institutional web sites, direct mailings, and advertisements in newspapers target- ing potential participants or organizations involved with the aging community. Physical and cognitive health were not used as wellli/o participation criteria. All participants and or their legally au- thorized representatives took part in the written informed consent process, as required by the Institutional Review Boards of the aforementioned institutions. Additional data collected included health and socio-demographic histories, proof of age, usually in the form of a birth certificate, a three-generation pedigree, and measures to assess functional independence and cognitive status. Anonymous controls, self-identified as ‘‘Cau- terete,1<5 casian’’ and 50 years of age (with an average age of 38.6 years), were obtained from several anonymous sources in the U.S.

he ability to survive to old age is partially under genetic influence, and the heritability of average life expectancy has 2 been estimated to be 25% (1–4). The genetic influence of achieving extreme old age might be even greater (5). Male and female siblings of centenarians have a 17- and 8-fold greater relative risk, respectively, of surviving to age 100 and about half the death rate from age 20 to age 100 of birth cohort-matched individuals (6).

French cohort. For the follow-up study, we accessed 564 French LLI who consented through the Chronos Project at the Foun- dation Jean Deausset. The cohort consisted of 92 men and 472 women, all Caucasian, and at least 99 years of age (mean 103.1) at the time of blood collection. Controls were selected from 564 unrelated Caucasians born in France and matched to the cohort with respect to geographic origin. The average age of this control group was 51.2 years (ages 18–70) at the time of sample collection.

Despite the challenges of studying complex traits such as lifespan, an increasing number of genetic studies are reporting genes influencing human longevity. These genes include ApoE, ApoB, and klotho (7–10), although only the ApoE association has been reproduced consistently. To achieve their extreme age, centenarians likely lack numerous gene variants that are asso- ciated with premature mortality, and they may be more likely to carry protective variants as well (11, 12).

We recently reported the results of a genomewide linkage scan using 308 extremely long-lived individuals (LLI) in 137 sibships. The results indicated linkage to exceptional longevity (defined as living beyond the 5% survival tail) at chromosome 4 near microsatellite D4S1564 with a maximum logarithm of odds score   of 3.65 (P 0.044 genomewide with nonparametric analysis) (13). No other chromosomal region achieved statistically signif- ——e  icant linkage in this study. There are 50 putative genes in the 12 million bp spanning the 85% confidence interval of this linkage peak, and a priori it was difficult to exclude any of the genes based on functional considerations. In addition, it was possible that the polymorphism underlying the linkage was not within any of these 50 putative genes. Therefore, an unbiased, systematic fine-mapping of the region was desired.