Reconciling the clk-1 and aging paradox and categorizing lifespan curves by taking individual specificity into account

The clk-1 gene encodes the demethoxyubiquinone (DMQ) hydroxylase that is required for biosynthesis of ubiquinone (coenzyme Q). Deletion of clk-1 was lethal in mice, and its mutation in C. elegans mildly extended lifespan, slowed physiological rate and led to sickness. We found that if growth retardation was taken into account the average lifespan of clk-1 mutants would not be prolonged or would be shortened. In addition, recent study showed that knocking down of clk-1 shortened lifespan. Although the extension of lifespan in clk-1 mutants was mild and was not observed sometimes, some progenies indeed had prolonged maximum lifespan even if retardation of growth was taking into account. These paradoxes implicate the existence of individual specificity in the aging process even in the same cohort, just like a drug is beneficial for some people while for others it is detrimental. We further categorized lifespan curves into five kinds of patterns according to the lifespan alternations observed in organisms: N (normal); L (long-lived); S (short-lived); F (flattened); ST (steepened), and found that the curve of clk-1 mutants fit into the F pattern. The reasons behind the individual specificity and its implications in aging process deserves further investigations.