Hemochromatosis associated with HLA-A3, but the appropriate screening test is serum transferrin saturation and ferritin levels
While this question stem is vague, the most likely diagnosis is Hereditary Hemochromatosis.
Iron accumulation causes free radical damage in organs:
Also notice patient + older brother are >40, which is when total iron body accumulates enough to cause symptoms.
Hemochromatosis (Auto Recessive HFE Gene on Ch.6) Labs :
↑↑ Serum Iron & Ferritin & Transferrin saturation