MTHFR and migraine disorder: Among the investigated candidate gene polymorphisms, the MTHFR C677T, TNF −308(G/A), NOS3 Glu298Asp, and NOS3 [VNTR (27 bp) in intron 4] provided the most consistent evidence for association with both migraine and glucose-related traits, whereas genetic variants in the INSR, ESR1, and PON1 candidate genes were less consistent.