The present invention relates to improved diagnostic methods for early detection of a risk for developing an arthritic disorder in humans, and screening assays for therapeutic agents useful in the treatment of arthritic disorders, by comparing the levels of one or more indicators of altered mitochondrial function. Indicators of altered mitochondrial function include enzymes such as mitochondrial enzymes and ATP biosynthesis factors. Other indicators of altered mitochondrial function include mitochondrial mass, mitochondrial number and mitochondrial DNA content, cellular responses to elevated intracellular calcium and to apoptogens, and free radical production. Methods of treating, and of stratifying, human patients as such methods relate to disclosed indicators of altered mitchondrial function are also provided.