- The thymidylate synthase tandem repeat polymorphism is not associated with homocysteine concentrations in healthy young subjects. Brown, K.S., Kluijtmans, L.A., Young, I.S., McNulty, H., Mitchell, L.E., Yarnell, J.W., Woodside, J.V., Boreham, C.A., McMaster, D., Murray, L., Strain, J.J., Whitehead, A.S. Hum. Genet. (2004)