POLG and myopathy: From these analyses and with the histopathological data available so far, three main phenotypes can be highlighted: (1) predominant neuropathy (e.g., RAD21-related) or ICC-related neuronal alterations (e.g., SGO1-related); (2) myopathy (e.g., ACTG2-dependent); (3) neuro-myopathy due to mitochondrial dysfunction (e.g., TYMP-, POLG-, and LIG3-related).