From http://www.myriadpro.com/ (a lab test company):
DPYD - A gene that makes the enzyme primarily responsible for metabolizing or breaking down 5-FU and clearing it from the body quickly. If DPYD enzyme activity is compromised, 5-FU is cleared more slowly, resulting in a longer period of exposure and a subsequent increase in toxicity. Patients with DPYD mutations have up to a 7-fold increased risk for dose-limiting toxicity from 5-FU treatment.
According to the same site, there's also:
TYMS - An essential enzyme for DNA synthesis. If a genetic variation causes underproduction of TYMS, only a portion of the 5-FU dose binds to and inhibits this enzyme; the rest remains unbound in the body, resulting in increased toxicity. Patients with variations in the TYMS gene have up to a 1.4- to 2.5-fold increased risk for dose-limiting toxicity from 5-FU.
Finally, according to the same site (who's business is to do these lab tests) says:
"Up to 25% of individuals have variations in the DPYD and/or TYMS genes that are associated with an increased risk of toxicity to 5-FU."
Terry wrote:Is your sister doing Xeloda or 5FU? There is something with 5FU in certain people that they are unable to metabolize the 5FU and it is VERY toxic and has taken the lives of a few people. There is a test for it but I can't remember what it is. Maybe someone else on here will remember more details.