Over follow-up and after the date of starting cART, the antiretroviral drugs received by the patients were lamivudine (72.7% of the follow-up time), stavudine (43.0%), zidovudine (41.7%), didanosine (19.4%), abacavir (11.7%), and tenofovir (8.5%); nevirapine (14.0%) and efavirenz (13.3%); and unboosted protease inhibitor (38.3%) and boosted protease inhibitor (21% of the follow-up).
Incidence and Predictors of Any Lipodystrophy
Among the 187 patients cumulatively contributing 947 person-years of follow-up (PYFU) (median of 4.67 years of follow-up per patient, range, 0.17–11.08), lipodystrophy was observed in 102 [incidence rate (IR) 10.8 per 100 PYFU, 95% confidence interval (CI): 8.8 to 13.1]. The estimates of the association between mitochondrial haplogroups and other analyzed factors with this outcome are shown in Table 3. Patients carrying mitochondrial haplogroup K, as compared with those carrying the most prevalent haplogroup H, showed a higher crude incidence of any lipodystrophy (IR 27.2 versus 8.8 per 100 PYFU, Fisher exact P = 0.007), whereas no difference was observed comparing H with any of the other haplogroups (P > 0.12).
In a multivariable model adjusting for a number of patients-related factors and antiretroviral variables, patients with haplogroup K showed a 4-fold higher risk of developing any lipodystrophy as compared with haplogroup H carriers. Other variables independently associated with a higher risk of lipodystrophy were female gender, older age, and higher current CD4 values, whereas a longer duration of exposure to tenofovir was associated with a reduced incidence of any lipodystrophy.
Incidence and Predictors of Lipoatrophy
Lipoatrophy developed in 84 subjects during 1022 person-years (IR 8.22, 95% CI: 6.6 to 10.1 per 100 PYFU). The association between the mitochondrial haplogroups and other factors with the incidence of lipoatrophy was analyzed using a competing-risk approach and summarized in Table 3. Patients carrying mitochondrial haplogroup K showed a similar crude incidence of lipoatrophy to that of haplogroup H carriers (IR 6.3 versus 7.2 per 100 PYFU, Fisher exact P = 0.82).
However, after adjusting for potential confounders, patients with haplogroup K showed >2-fold higher risk of developing lipoatrophy as compared with haplogroup H carriers, although not significant (P = 0.09).
A similar but not significantly higher risk for lipoatrophy was observed in haplogroup T carriers as compared with patients with haplogroup H.
Other variables independently associated with a higher incidence of lipoatrophy were higher current CD4 values and the specific nucleoside pair currently in use, whereas a longer duration exposure to tenofovir was, again, associated with a reduced incidence. The same analyses were conducted using the cause-specific approach. The multivariable analysis showed that haplogroup K carriers had an independently higher risk of lipoatrophy, which was 3-fold higher as compared with haplogroup H carriers (hazard ratio 2.99, 95% CI: 1.10 to 8.11, P = 0.03).
Moreover, the independent associations of the other variables with the risk of lipoatrophy were confirmed by this approach. Furthermore, female sex and the older age category were also associated with an independently higher risk of this event.
To verify the hypothesis that the age-associated fat loss may have been different according to gender, we formally tested the interaction between gender and age. We found no evidence for such an interaction: the relative risk of lipoatrophy associated with an age of >35 versus ≤35 years was 1.39 (95% CI: 0.68 to 2.84) in female subjects and 1.12 (95% CI: 0.62 to 2.04) in male subjects (interaction P = 0.66).
Incidence and Predictors of Fat Accumulation
Fat accumulation was observed in 57 patients during 1175 person-years (IR 4.85, 95% CI: 3.7 to 6.2 per 100 PYFU). The association between mitochondrial haplogroups and other factors with the risk of fat accumulation are summarized in Table 3. There was no evidence that the crude incidence of fat accumulation was higher in a certain haplogroup as compared with another. Only in univariate analysis the risk for patients with haplogroup J tended to be higher than that of patients carrying the haplogroup H (IR 9.2 versus 4.1 per 100 PYFU, Fisher exact P = 0.09).
In the multivariable analysis, patients with haplogroup K showed a higher risk of developing fat accumulation as compared with those with haplogroup H carriers, although statistical significance was obtained only when the cause-specific approach to the analysis was employed (hazard ratio 5.27, 95% CI: 1.31 to 21.13, P = 0.02).
Other variables independently associated with a higher risk of fat accumulation in the main competing-risk analysis were a higher current CD4 values and the specific nucleoside pair currently in use, whereas the longer exposure to tenofovir was, again, an independent predictor of a reduced risk of fat accumulation. The same variables showed similar associations with this outcome also when using the cause-specific approach (not shown).
In this largely prospective study, we observed an association between the presence of mitochondrial haplogroup K and the risk of lipodystrophy of any type. When we evaluated fat loss and fat accumulation separately using a competing-risk approach, our analysis showed a similar trend; however, the association was not statistically significant, possibly because of reduced power.
In an alternative cause-specific analysis approach, the associations were stronger and, especially in the analysis of lipoaccumulation, a large difference in the magnitude of risks between patients carrying H and K haplogroups was shown. This association was independent of the other studied patients and treatment-related characteristics. Female patients with higher current levels of CD4 and the type of currently used nucleoside reverse transcriptase inhibitor pair also showed independently higher risks of all lipodystrophy outcomes, whereas older age predicted a higher risk of lipoatrophy only, and longer exposure to tenofovir was associated with a reduced risk of lipodystrophy.
In contrast, current use of tenofovir seemed to be associated with an increased risk of fat distribution. Although this may sound contradictory, this finding may simply be explained by a prescription bias of tenofovir to patients perceived at risk.
We have chosen the competing-risk approach as our main analysis to make the interpretation of results easier as the risk of developing different aspects of the lipodystrophy syndrome (fat loss versus accumulation) are unlikely to be independent. In a smaller prospective study, with a shorter follow-up, haplogroup J carriers tended to be associated with a lower risk of limb fat loss as measured by dual-energy x ray absorptiometry, as compared with patients carrying other mitochondrial haplogroups.21
In our series we could not confirm this association, although there was a tendency for a lower risk when comparing J and H, especially in patients who were currently exposed to either didanosine or stavudine (data not shown). The discrepancy with the previously published report may partially depend on the different outcomes definition and on a different treatment exposure in the 2 study populations.
In another report, mitochondrial haplogroups, which were characterized using an identical technique as in this study,18 were not associated with differences in quantitative body fat measures in patients referred for lipodystrophy. Discrepancies can be explained by study design, because the published report is a prevalent cohort with a cross-sectional design, whereas our study prospectively analyzes incidence.
In a different study, haplogroup H was strongly associated with HIV lipoatrophy, whereas the haplogroup T had a slightly protective role. Potential differences that may well explain the discordances observed with our study are the population that was only composed of male subjects, and the study design that was based on a single cross-sectional assessment of the atrophic component of lipodystrophy.22
Haplogroup K carriers are relatively rare among whites: our 6% prevalence is in line with the existing data (4.1%–13.5%).9,23,24 This haplogroup is defined by nucleotide substitution G9055A in the ATP6 gene of mitochondrial DNA, which leads to an alanine to threonine substitution.
The pathogenic mechanism underlying the association between this specific mitochondrial haplogroup K and the higher incidence of lipodystrophy during cART remains unexplained and requires further investigation. It might be hypothesized that variations of mitochondrial DNA leading to haplogroup classification are associated with a reduced mitochondrial function, which may exacerbate the mitochondrial toxicity of antiretroviral treatment by modulating ATP production. Moreover, mitochondrial DNA variation may be associated with increased apoptosis of adipocytes, which may explain the association with the lipoatrophy component but not with the fat accumulation. Alternatively, haplogroup K may be in linkage disequilibrium with other gene variants involved in the development of fat accumulation or lipoatrophy.20
The association of female gender with lipoatrophy and fat accumulation and of older age with lipoatrophy is not unexpected and confirms previous observations.20,25 The association of the different types of lipodystrophy with higher current CD4 counts is likely to be explained by a longer exposure to cART and consequently to its long-term toxicity. Finally, the inverse correlation between a longer duration exposure to tenofovir and the risk of lipoatrophy and fat accumulation suggests a lower potential for this drug to cause mitochondrial toxicity and abnormal fat accumulation as shown in other studies.3,26
Among the limitations of this study there is the phenotype definition that may have resulted in an underestimate of the true incidence of the lipodystrophy outcomes as compared with studies using imaging techniques and dual-energy x ray absorptiometry for the outcomes definition.26 On the other hand, the alterations perceived by the patient and observed by the clinician could be more relevant in terms of patients' quality of life. Moreover, the validity of the assessment of lipodystrophy using an objective physical examination for analyzing the association with other genetic variants has been previously established.20
Another limitation is represented by limited numbers of observations for each of the haplogroups. The major strength of our analysis is represented by the long duration of the prospective follow-up (5.0–6.1 years, on average, depending on the specific end point).
Should our results be repeated by other studies including patients from different ethnic backgrounds, mitochondrial DNA variation could be investigated to identify genetic predisposition to abnormalities leading to fat redistribution observed during prolonged combination antiretroviral treatment.
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Keywords:© 2012 Lippincott Williams & Wilkins, Inc.
HIV-1; mitochondria; genomics; lipodystrophy; toxicity