In many countries there are centers specialized in mitochondrial diseases. These centers are networked and regularly exchange information on research and patient issues.
Germany and Austria:
https://www.mitonet.org/netzwerk/teilnehmende-zentren/
USA:
https://www.umdf.org/find-a-doctor/
United Kingdom:
https://mitochondrialdisease.nhs.uk/
France:
https://carammel.org/network