DPYD and dihydropyrimidine dehydrogenase deficiency: Subsequent analysis of the DPD activity in fibroblasts of the 3 patients and a known patient with DPD deficiency, due to homozygosity for the NM_000110.4:c.1905+1G>A variant in DPYD, showed no DPD activity in fibroblasts cultured at 37°C.