GSTM1 and migraine disorder: Akin et al. have shown that amplitudes of deoxygenated hemoglobin (Hb) and oxygenated hemoglobin (HbO2) signals acquired by NIRS are approximately two to five times higher in controls than migraine patients during four consecutive breath-holding tasks and concluded their results as a confirmation of an impaired cerebrovascular reactivity in the frontal cortex of migraine patients [4].