Fibroblasts taken from two genetic PD patients exhibited dampened oscillations in bioenergetic activities, reduced rates of mitochondrial oxygen consumption, and dysregulated TTFL factor expression patterns - CLOCK, CRY1, and CRY2 were upregulated while PER2 was downregulated in these cells (Pacelli et al., 2019). Here, PER2 is linked to Parkinson disease.