MTHFR and Respiratory tract infection: Fifteen of the 25 patients had variable associated risk factors, such as heart failure (one case), oral contraceptives (one case), septic arthritis (one case), ulcerative colitis (one case), lupus anticoagulant (one case), cardiac surgery (one case), high homocysteine levels due to a MTHFR mutation (one case), respiratory tract infection (one case), Churg-Strauss vasculitis (one case), DVT (one case).