A protective effect of skewed XCI pattern due to pathogenic variants in the NDUFB11 gene has been previously suggested in two healthy mothers of three females with an X-linked dominant MLS syndrome with histiocytoid cardiomyopathy, epilepsy, developmental delay, failure to thrive and hypotony [24], as well as in a healthy mother and sister of a 23-year-old male presenting with sideroblastic anemia, myopathy and lactic acidosis [17]. The gene discussed is NDUFB11; the disease is sideroblastic anemia.