Is ACTN3 useful for Müdigkeit?

The short answer: ACTN3 is not a useful marker for fatigue. This gene encodes α-actinin-3, a structural protein in fast-twitch (type II) muscle fibers. The common R577X polymorphism leads to a deficiency in about 18% of Europeans. Some studies suggest that ACTN3 deficiency may slightly reduce sprint performance and increase muscle fatigue during high-intensity exercise, but the effect on general fatigue is small and inconsistent. Fatigue is multifactorial—sleep, nutrition, stress, iron status, thyroid, and mental health are far more relevant. A DNA test for ACTN3 cannot diagnose or guide treatment for fatigue. Evidence is mechanistic and based on athletic cohorts, not clinical fatigue patients. MyBody-X may include ACTN3 in a sports panel, but for fatigue workup, standard blood biomarkers (ferritin, B12, TSH, CRP, CBC) are recommended. Conclusion: ACTN3 is not useful for fatigue; evidence level is weak (mechanistic/mixed).