Table 2.

Effect of genetic polymorphisms on water-soluble vitamins

Vitamin	Gene	Protein function	Polymorphism	Effect of genetic polymorphisms on vitamins	Disease associated with vitamin deficiency or excess	Ref.
B12	FUT2	Fucosyl transferase; transporter required for cellular uptake of B12	rs602662 (772G>A)	Low concentrations of cellular and plasma vitamin B12 in G allele carriers	Deficiency: pernicious anemia	[44]
	TCN2	Transcobalamin II; transfer protein of vitamin B12	rs1801198 (776C>G)	Significantly lower levels of haptocorrin–vitamin B12 complex, lower percentage of total transcobalamin–vitamin B12 in GG allele carriers		[45]
C	SVCT2 (SLC23A2)	Sodium-dependent vitamin C transporters; transporter responsible for intake and discharge of ascorbic acid to maintain the homeostasis of vitamin C	rs6139591	Higher risk of acute coronary syndrome when taking lower median dietary vitamin C in TT allele carriers	Deficiency: scurvy and skin purpura; gum bleeding Excess: urinary stones	[47]
			rs1776964	More vitamin C absorption in TT allele carriers than carriers of CC genotype.
Folic acid	MTHFR	Methylenetetrahydrofolate reductase; major enzyme for folic acid metabolism	rs1801133 (677C>T)	Higher risk of cardiovascular diseases in TT allele carriers than C allele carriers	Deficiency: giant young red blood cell anemia, leukopenia	[52]
	SLC19A1 (RFC-1)	Solute carrier family 19 member 1; transporting folic acid across the placenta and the blood–brain barrier	rs1051266 (80A>G)	Higher risk to have Down syndrome children in GG allele carriers