HTRA2 and Parkinson disease: Based on the critical involvement of mitochondrial function in neurodegeneration and aging processes and due to the role of mutations in the Omi/HtrA2 gene as possible susceptibility factors in PD [9,10], we studied the consequences of loss of Omi/HtrA2 protein in fibroblasts from knockout mice [6] as well as in silenced human HeLa and Drosophila melanogaster S2R+ cells.