FOS and Alpers syndrome: However, 7 of 13 patients with Alpers’ syndrome, 3 of 5 patients with late-POLG disease, and 4 of 10 patients with mtDNA disease showed detectable levels of c-Fos, in total constituting 50% of the patient cohort (Table 3, Supplementary Fig. 6), suggesting recent neuronal hyperactivity.