Severe fluoropyrimidine toxicity due to novel and rare DPYD missense mutations, deletion and genomic amplification affecting DPD activity and mRNA splicing

• Published in: Biochimica et biophysica acta 2017-03, Vol.1863 (3), p.721-730
• Main Authors: van Kuilenburg, André B.P., Meijer, Judith, Maurer, Dirk, Dobritzsch, Doreen, Meinsma, Rutger, Los, Maartje, Knegt, Lia C., Zoetekouw, Lida, Jansen, Rob L.H., Dezentjé, Vincent, van Huis-Tanja, Lieke H., van Kampen, Roel J.W., Hertz, Jens Michael, Hennekam, Raoul C.M.
• Format: Article
• Language: English
• Subjects: 5-Fluorouracil; Capecitabine; Dihydropyrimidine dehydrogenase; DPYD; Pharmacogenetics; Toxicity
• ISSN: 0925-4439; 0006-3002; 1878-2434; 1879-260X
• DOI: 10.1016/j.bbadis.2016.12.010

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (5FU). Genetic variations in DPD have emerged as predictive risk factors for severe fluoropyrimidine toxicity. Here, we report novel and rare genetic variants underlying DPD deficiency in 9 cancer patients presenting with severe fluoropyrimidine-associated toxicity. All patients possessed a strongly reduced DPD activity, ranging from 9 to 53% of controls. Analysis of the DPD gene (DPYD) showed the presence of 21 variable sites including 4 novel and 4 very rare aberrations: 3 missense mutations, 2 splice-site mutations, 1 intronic mutation, a deletion of 21 nucleotides and a genomic amplification of exons 9–12. Two novel/rare variants (c.2843T>C, c.321+1G>A) were present in multiple, unrelated patients. Functional analysis of recombinantly-expressed DPD mutants carrying the p.I948T and p.G284V mutation showed residual DPD activities of 30% and 0.5%, respectively. Analysis of a DPD homology model indicated that the p.I948T and p.G284V mutations may affect electron transfer and the binding of FAD, respectively. cDNA analysis showed that the c.321+1G>A mutation in DPYD leads to skipping of exon 4 immediately upstream of the mutated splice-donor site in the process of DPD pre-mRNA splicing. A lethal toxicity in two DPD patients suggests that fluoropyrimidines combined with other therapies such as radiotherapy might be particularly toxic for DPD deficient patients. Our study advocates a more comprehensive genotyping approach combined with phenotyping strategies for upfront screening for DPD deficiency to ensure the safe administration of fluoropyrimidines.