Frequencies of mtDNA haplogroup clusters among Vitality 90+ cases and controls

We then analysed the frequencies of the clusters of phylo- genetically related haplogroups HV, UK, TJ and WIX. Again, the Vitality 90+ group and the controls differed (P=0.002; Table 2), the frequency of cluster HV being lower among the Vitality 90+ cases (P=0.001), whereas that of cluster UK was higher (P=0.014). The number of samples belonging to cluster WIX was almost twice as high in the Vitality 90+ group as in the controls (P= 0.078).

The Vitality 90+ cases also differed from the infants in this respect (P=0.00001), their frequency of cluster HV being significantly lower (P=0.001), whereas those of clusters WIX (P=0.048) and UK (P=0.05) were higher and that of cluster TJ significantly higher (P=0.004). The controls and the infants did not differ significantly from each other (Table 2).

The maternal lineage of the Vitality 90+ group and the two anonymous control groups was not known introduc- ing a possible confounding effect. However, the Finnish population is ethnically homogeneous and immigration from other countries has been negligible (Korkiasaari and Söderling 1994). Migration within Finland remained at approximately 4% in the 20th century, increasing only to 5.5% between 1946–1950 (Koskinen et al. 1994). The set- tlement of Finns from southeastern Karelia after World War II has probably not affected the mtDNA gene pool, as there is no difference in haplogroup frequencies between the present Karelians and Finns (Simoni et al. 2000). Ho- mogeneity among the three groups is further suggested by the observations that an mtDNA lineage introduced by earlier founders will make a larger contribution to the contemporary population than lineages introduced later (Heyer 1995). Therefore, we believe that the differences detected between Vitality 90+ and the two control groups represent true differences.

Association between mtDNA haplogroups and clinical phenotypes

The genotype-phenotype association was studied in the Vitality 90+ group after stratification according to the

Table 2 Frequencies of mtDNA haplogroup clusters among the Vitality 90+ subjects, controls and infants

Cluster Cluster frequencies Vitality 90+ Controls Infants n % n % n % HV 88 39.1 220 55.0 154 59.9 WIX 21 9.3 22 5.5 12 4.7 TJ 30 13.3 47 11.8 14 5.4 UK 81 36.0 106 26.5 71 27.6 Other 5 2.2 5 1.3 6 2.3 Total 225 99.9 400 100.1 257 99.9

Like our finding that the frequency of haplogroup J in- creases with the age of the population, an association be- tween this European-specific mtDNA haplogroup and longevity has also been reported among Italian centenari- ans (De Benedictis et al. 1999). Interestingly, we have found that the frequency of subcluster J2 is higher among the Vitality 90+ subjects than among the controls. Differ- ences in the frequencies of haplogroup J subclusters have

also been reported in Irish centenarians and controls (Ross et al. 2001) but, unfortunately, the assignment to subclus- ters was based on the nucleotide sequence in HVS-I, thus not allowing comparison with the present data. Sequenc- ing of HVS-I in Italian centenarians and controls has not revealed any clustering into a specific haplotype within haplogroup J (Rose et al. 2001). It has been suggested, however, that this haplogroup modulates the phenotypic → expression of the mtDNA mutations 11778G A and → 14484T C that cause Leber’s hereditary optic neuropa- thy (LHON; Brown et al. 1997; Lamminen et al. 1997; Torroni et al. 1997), and the frequency of subcluster J1 has been found to be 8-fold among patients with LHON relative to controls (Torroni et al. 1997), suggesting that this subcluster increases the deleterious effect of an mtDNA mutation. Our data do not contradict this finding, as they suggest that subcluster J2 is beneficial in ageing. → The nucleotide substitution 9055G A defining hap- logroup K is higher among French centenarians than among the controls (Ivanova et al. 1998) and we have found that this haplogroup is more frequent in the Vitality 90+ group (7.6%) than in either the controls (6.0%) or the infants (4.7%). Furthermore, the only clinical association among the Vitality 90+ subjects is between diabetes mel- litus and haplogroup K.

Relative frequency of haplogroupsamong Vitality 90+06040,20,0  T5 6 7 8 9 10Average number of polymorphisms in haplogroup

Average number of polymorphisms in haplogroup

Fig.1 Relative frequencies of mtDNA haplogroups among the Vi- tality 90+ subjects, plotted against the average numbers of poly- morphisms in haplogroups. The average numbers of non-synony- mous substitutions in the structural genes and substitutions in genes encoding ribosomal RNAs and tRNAs were calculated for each haplogroup, by making use of 192 Finnish mtDNA sequences (Finnilä et al. 2001). The haplotype lying between the African, Asian and European haplogroups was taken to be the most recent common ancestor. A sigmoidal fit to the data points is shown (χ2 test, P=0.068). The capital letters refer to mtDNA haplogroups. Haplogroups I, W and X were not included in the analysis, because their frequencies were below 4% in both of the control groups