Severe toxicity to capecitabine due to a new variant at a donor splicing site in the dihydropyrimidine dehydrogenase (DPYD) gene

Abstract

Severe, life-threatening adverse reactions to capecitabine sometimes occur in the treatment of solid tumors. Screening for dihydropyrimidine dehydrogenase (DPYD) deficiency is encouraged before start of treatment, but the genetic variants that are commonly analyzed often fail to explain toxicities seen in clinical practice. Here we describe the case of a 79-year-old Caucasian female with breast cancer who presented with life-threatening, rapidly increasing toxicity after 1 week of treatment with capecitabine and for whom routine genetic DPYD test resulted negative. DPYD exon sequencing found variant c.2242+1G>T at the donor splicing site of exon 19. This variant is responsible for skipping of exon 19 and subsequent generation of a non-functional DPYD enzyme. This variant has not been described previously but was found in three other members of the patient's family. With this case, we show that exon sequencing of DPYD in patients who experience marked toxicity to fluoropyrimidines and test negative for commonly evaluated variants can prove extremely useful for identifying new genetic variants and better explain adverse reactions causality.

Keywords: adverse drug reaction; breast cancer; fluoropyrimidine; pharmacogenetics.

Figure 1

Sequence electropherogram of the 2242+1G>T variant. Blue, dCTP; green, dATP; black, dGTP; red, dTTP. Abbreviations: dATP, deoxyadenosine triphosphate; dCTP, deoxycytidine triphosphate; dGTP, deoxyguanosine triphosphate; DPYD, dihydropyrimidine dehydrogenase; dTTP, deoxythymidine triphosphate.

Figure 2

Exon skipping sequence. Notes: Left: Electrophoresis of amplified cDNA from peripheral blood mononuclear cells of a patient carrying the 2242+1G>T variant. Right, upper: Graphic representation of skipping of exon 19. Right, lower: Sequence electropherogram using the primer Ex18F. A double sequence is observed for 85 nucleotides corresponding to overlapping of exons 19 and 20.

Figure 3

Structures of wild-type DPYD and truncated DPYD. Notes: The interpretation of mutation effect and the molecular modeling were performed by using Deep View Swiss-PDB viewer and Tasser. (A) Modeling of wild-type DPYD; (B) modeling of truncated DPYD.