For these reasons, the thinning of human AAA wall may be linked to a reduction in H2S production that up-regulates the mPGES-1/PGE2/EP4/MMP axis, a reversal of the regulatory processes that result in wall thickening in varicose veins and pulmonary hypertension as previously described. The gene discussed is PTGES; the disease is pulmonary arterial hypertension.