MTHFR and Marfan syndrome: Thirty-three publications were further excluded after review of full-text because of the following reasons: subjects with Down/Turner/Marfan Syndrome (5 studies), no report of the association between MTHFR C677T polymorphism and CHDs (4 studies), without case-control or TDT design (11 studies), data duplication (6 studies) and lack of sufficient data (7 studies).