Key: SD, standard deviation; MRC, Medical Research Council.

2.2. Molecular genetic analysis

3. Results

mtDNA haplogroups were determined using a stepwise algo- rithm (Torroni et al., 1996) by primer extension of multiplex polymerase chain reaction products with the detection of the allele- specific extension products by matrix-associated laser desorption/ ionization time of flight (Sequenom MassARRAY, San Diego, CA, USA). DNA was available for 752 participants; 52 cases were excluded from the analysis because of either heteroplasmic status (n ¼ 5) or inability to detect haplogroup/low-quality DNA (n ¼ 47), leaving 700 with valid mitochondrial haplogroup data.

The overall frequency distribution of mtDNA haplogroups in the incident Newcastle 85þ cohort was compared with the birth cohort (p ¼ 344), mid-age cohort (p ¼ 2889), and old-age cohort (p ¼ 93) (Table 1). The only significant difference in distributions was for the local older cohort that differed from each of the other cohorts in the “other” haplogroup category only.

There was no significant association between mtDNA hap- logroups and frailty (RFI or FFS) before and after controlling for the potential confounding variables (Tables 2 and 3). Although we observed an association between haplogroup X and increased mortality(p¼0.025),thiswasnotapparentaftercontrollingfortotal cholesterol, body mass index, hypertension, diabetes, ethnicity, and smoking status (Table 4). Likewise, the trend toward reduced mortalityassociatedwithhaplogroupK(p¼0.041),whichremained after controlling for other variables (p ¼ 0.023), did not withstand correction for the multiple haplogroups under investigation.

2.3. Statistical analysis

The frequency of mtDNA haplogroups in the incident Newcastle 85þ cohort (n ¼ 700) was compared with 3 ethnically matched population control data sets representing different ages using chi-squared analysis with pairwise comparisons of samples for each haplogroup: (1) a local birth cohort (n ¼ 344, neonatal cord blood samples), North Cumbria Community Genetics Project (Elliott et al., 2008); (2) a national mid-age cohort, the 1958 Medical Research Council cohort (n ¼ 2889, 52% male), which has previously been shown to be representative of control subjects in our region (Chinnery et al., 2007); and (3) a local cohort of

4. Discussion

We found no robust evidence of an association between mtDNA haplogroups and either frailty or survival beyond age 85 or any

Table 2

RFI and mitochondrial haplogroupdregression coefficients (unstandardized) for square rootetransformed RFI by mitochondrial haplogroupa

Haplogroup Model 1, unstandardized regression Model 1, Model 2, unstandardized Model 2, Model 3, unstandardized Model 3, coefficient (95% confidence interval) p value regression coefficient p value regression coefficient p value (95% confidence interval) (95% confidence interval) H 0.015 ((cid:2)0.003 to 0.034) 0.101 0.017 ((cid:2)0.001 to 0.036) 0.065 0.013 ((cid:2)0.006 to 0.031) 0.175 Non-H Reference Reference Reference T (cid:2)0.006 ((cid:2)0.037 to 0.024) 0.684 (cid:2)0.009 ((cid:2)0.040 to 0.021) 0.536 (cid:2)0.007 ((cid:2)0.036 to 0.023) 0.663 Non-T Reference Reference Reference J (cid:2)0.016 ((cid:2)0.045 to 0.014) 0.300 (cid:2)0.014 ((cid:2)0.043 to 0.015) 0.338 (cid:2)0.011 ((cid:2)0.040 to 0.018) 0.455 Non-J Reference Reference Reference U (cid:2)0.009 ((cid:2)0.035 to 0.016) 0.481 (cid:2)0.009 ((cid:2)0.034 to 0.016) 0.488 (cid:2)0.008 ((cid:2)0.033 to 0.017) 0.526 Non-U Reference Reference Reference K (cid:2)0.033 ((cid:2)0.068 to 0.003) 0.069 (cid:2)0.033 ((cid:2)0.068 to 0.002) 0.064 (cid:2)0.029 ((cid:2)0.064 to 0.007) 0.112 Non-K Reference Reference Reference X 0.060 ((cid:2)0.008 to 0.128) 0.083 0.057 ((cid:2)0.010 to 0.124) 0.098 0.053 ((cid:2)0.014 to 0.120) 0.122 Non-X Reference Reference Reference W 0.015 ((cid:2)0.040 to 0.071) 0.585 0.012 ((cid:2)0.043 to 0.066) 0.675 0.018 ((cid:2)0.037 to 0.072) 0.523 Non-W Reference Reference Reference I 0.052 ((cid:2)0.022 to 0.126) 0.170 0.047 ((cid:2)0.026 to 0.120) 0.206 0.051 ((cid:2)0.022 to 0.123) 0.169 Non-I Reference Reference Reference V (cid:2)0.019 ((cid:2)0.068 to 0.031) 0.461 (cid:2)0.020 ((cid:2)0.069 to 0.029) 0.424 (cid:2)0.020 ((cid:2)0.069 to 0.028) 0.410 Non-V Reference Reference Reference

a Linear regression models were fitted with RFI (square root transformed to give adequate model fit) as the dependent variable and mitochondrial haplogroup as the independent variable. Seven binary variables were created of “in haplogroup H” versus “not in haplogroup H” type, and 7 models were run entering each binary variable separately. Model 1 is unadjusted, model 2 adjusted for sex, and model 3 adjusted for sex, education, and smoking status.

Table 3

FFS and mitochondrial haplogroupdodds ratio (95% confidence interval) of being in a frailer Fried category (pre-frail versus robust or frail versus pre-frail) by mitochondrial haplogroupa