Analysis of HLA-DQA, HLA-DQB Frequencies in a Group of Sardinian Centenarians

LETIZIA SCOLA,1 DOMENICO LIO,1 ANTONIO CRIVELLO,1 GIUSEPPINA CANDORE,1 GIUSI IRMA FORTE,1 GIUSEPPINA COLONNA-ROMANO,1 MARIO GIOVANNI PES,2 CIRIACO CARRU,2 LUIGI FERRUCCI,3 LUCA DEIANA,2 GIOVANNELLA BAGGIO,4 CLAUDIO FRANCESCHI,3,5 and CALOGERO CARUSO

Human leukocyte antigen (HLA) alleles, regulating type and intensity of the immune re- sponse, might influence life expectancy. In previous case-control studies the authors have demonstrated that both HLA-DR and -DQ alleles are not associated with longevity in the Sar- dinian population. On the other hand, association studies are subjected (as part of the ho- mogeneity of the population in terms of geographic origin) to a number of possible con- founding factors. Therefore, the authors typed the HLA-DQA1 and HLA-DQB1 alleles in 24 sibs (age range 85 to 97) of 17 centenarians by PCR-SSP. Sib pair analysis showed non- significant differences between the observed and expected percentage of DQA* or DQB1* al- lele sharing. Therefore, these data strengthen the view that class II HLA genes have a mar- ginal effect, if any, on the complex longevity trait.

type, although other studies do not confirm these observations.3,4 More recently, the au- thors evaluated HLA-DRB1 frequency in Sar- dinian centenarians and controls, and showed that HLA-DRB1*15 was increased in centenar- ians, although it was no more significant after Bonferroni’s correction.5 Indeed, association studies are subjected to a number of possible confounding factors, such as the homogeneity of the population in terms of geographic ori- gin.3 Selection of a very homogeneous popula- tion might allow one to overcome some con- founding biases. In this regard, the Sardinian

INTRODUCTION

T on the HE INFLUENCE OF GENETIC FACTORS variation in life expectancy might be esti- mated to be approximately 25%,1 and a num- ber of studies have suggested that genetic de- terminants of longevity might at least partially reside in the polymorphisms for genes that regulate immune responses as human leuko- cyte antigen (HLA) genes.2 Some well-planned and -designed association studies performed in whites suggest that longevity is associated with the HLA-DR11 allele or HLA-B8,DR3 haplo-

1Immunosenescence Unit, Department of Pathobiology and Biomedical Methodology, University of Palermo,

Immunosenescence Unit, Department of Pathobiology and Biomedical Methodology, University Palermo, Italy.

Biochemistry Clinic, University of Sassari, Sassari, Italy.

INRCA Geriatric Department, Laboratory of Clinical Epidemiology, Florence, Italy.

Operative Unit of General Medicine, Padova Hospital, Padova, Italy.

Department of Experimental Pathology, University of Bologna, Bologna, Italy.

HLA-DQ typing

population is an ancient genetic isolate, the ge- netic pool of which is characterized by rela- tively little genetic flow from the different pop- ulations that have invaded the island during the last 3000 years.6 On the other hand, the HLA region contains a remarkable number of genes forming some very stable haplotypes, characterized by a strong linkage disequilib- rium, and probably conferring a selection ad- vantage.7 Some of the highly conserved haplo- types are composed by the HLA-DR,DQ alleles and, in some instances, HLA-DQ alleles seem to play a central role in association with dis- eases.8,9 This study evaluated the effect of HLA-DQ alleles in determining a longevity trait. The analysis of affected sib pairs was ap- plied to 24 Sardinian centenarian-sib (85- to 99- year-old) pairs. This strategy, indeed, is an al- ternative powerful tool, allowing the authors to analyze the influence of genetic variants in- volved in complex phenotypes on ancestry and environmental influences independently.10

Blood specimens were collected in tripotas- sium EDTA sterile tubes and genomic DNA   was extracted and stored at 20°C for the dif- ferent genetic analyses. DNA samples for HLA- DQ typing were available from 123 centenari- ans (83 women and 40 men), 92 controls (58 women and 34 men), and 24 sibs (14 women and 10 men) of 17 centenarians (7 women and 10 men). HLA-DQ alleles of all the subjects were genotyped by amplification refractory mutation system/polymerase chain reaction using primer sets and PCR conditions de- scribed by Bunce et al.12

Statistics

Pearson’s test was applied to analyze differ- ences among expected and observed HLA DQA1* and DQB1* identity, haploidentity, or nonidentity frequencies in sib pairs.

RESULTS AND DISCUSSION

MATERIALS AND METHODS

HLA alleles and haplotypes have been se- lected throughout evolution, conferring resis- tance to infectious disease both via peptide pre- sentation and regulating type and intensity of the immune response.3,4,7 Nevertheless, HLA- DR,DQ alleles and, in some instances, HLA-DQ alleles, seem to play a central role in associa- tion with diseases.9,13–15 As previously re- ported,16 nonsignificant differences in HLA- DQA1* and -DQB1* allele frequencies were found between centenarians and controls (data not shown). On the other hand, for extreme longevity, moderate familial clustering also has been observed. Perls and coworkers found that the survival ratio for siblings of centenarians versus siblings of 73-year-olds was about four- fold that for people aged 80 to 94.17 A recent report on Danish centenarians suggests that siblings born after centenarians have a fourfold increased chance of becoming centenarians compared to their birth cohort.18 Table 1 de- scribes the results of HLA-DQ allele typing of centenarian sib pairs. The authors have not in- vestigated the association of each single DQ al- lele to longevity, because analysis of affected sib-pairs with different methods of localizing

Subjects