- To identify individuals who may require a non-standard dose of anti-cancer agent, 5-FU
- To assess the cause of excessive toxicity from 5-FU treatment.
DPYD is the rate limiting enzyme involved in the catabolism of pyrimidines,
i.e., thymidine and uracil. DPYD is also the main enzyme involved in the degradation of structurally related compounds like 5-Fluorouracil (5-FU), a widely used anticancer drug. Some patients carry a variant of DPYD gene that causes reduced quantity of protein. In these patients, the lack of enzymatic activity increases the half-life of the drug, resulting in excess drug accumulation and toxicity.
A guanine to adenine point mutation in the 5′-splice site consensus sequence has been reported in patients with DPYD deficiency.
It is recommended that screening for this mutation should be accompanied by direct measurement of DPYD activity prior to 5-FU treatment in cancer patients.
The human DPYD gene is located on chromosome 1 (1p22). The following three genotypes of the DPYD gene are possible:
(-/-) – Normal
(-/+) – Heterozygous
(+/+) – Homozygous
DPYD deficiency affects approximately 5 % of the overall population.
The test was developed using CLSI guidelines. Control DNA samples of known genotypes are tested together with each patient sample to monitor the performance of the test. Genomic DNA is extracted from the submitted specimen and analyzed by Polymerase chain reaction (PCR) followed by restriction digest.
Whole blood in a purple top (EDTA) tube
• Blood specimen:
– It is collected in a heparin-containing tube because heparin can inhibit the PCR reaction.
– It leaked in the shipping container.
– The name on the tube does not match the name on the paperwork.
– It is older than 10 days.
Homozygous wild-type (-/-): Normal DPYD activity
Heterozygous (-/+): Decreased DPYD activity may cause increased risk of toxicity to 5- FU.
Homozygous mutant (+/+): Significantly decreased DPYD activity may cause increased risk of toxicity to 5-FU.
Other genetic variants of the DPYD gene that are not detected in this assay may influence DPYD activity. The detection of genetic variants does not replace the need for appropriate clinical monitoring by the health care provider. It is recommended that screening for this mutation should be accompanied by direct measurement of DPYD activity prior to 5-FU treatment in cancer patients. These tests were developed and the performance characteristics were determined by MDL. This test has not been cleared or approved by the US Food and Drug Administration.
Gonzalez FJ, Fernandez-Salguero P. (1995) Diagnostic analysis, clinical
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van Kuilenburg AB, Vreken P, Beex LV, De Abreu RA, van Gennip AH. (1998) Severe 5-fluorouracil toxicity caused by reduced dihydropyrimidine dehydrogenase activity due to heterozygosity for a G–>A point mutation. J. Inherit. Metab. Dis. 21:280-4.
Wei, X., McLeod, HL., et al.(1996) Molecular basis of the human dihydropyrimidine dehydrogenase deficiency and 5-fluorouracil toxicity. J. Clin. Invest. 98:610-615, 1996
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Lee A, Ezzeldin H, Fourie J, Diasio R. Dihydropyrimidine dehydrogenase deficiency: impact of pharmacogenetics on 5-fluorouracil therapy. Clin Adv Hematol Oncol. Aug 2004;2(8):527-32.
For more information go to National Center for Biotechnology Information (NCBI).