Wu et al (2014) investigated whether genetic mutations of the SHMT, MS, MTRR and CBS genes can affect Homocysteine (Hcy) levels and are associated with breast cancer. Results showed those with elevated Hcy levels had a 4.45 increased risk of breast cancer when comparing breast cancer patients with healthy controls. Results suggested it is mutations of specific genes coding the SHMT, MS, MTRR and CBS enzymes may be factors that contribute to increased plasma levels of Hcy. Mutations of the SHMT, MS and MTRR genes were also found to be associated with breast cancer risk. The authors state plasma Hcy levels and hence these mutations involved in the methylation cycles could be metabolic risk factors for breast cancer risk.