DPYD and dihydropyrimidine dehydrogenase deficiency: Dihydropyrimidine dehydrogenase (DPD) deficiency is a rare autosomal recessive disorder of pyrimidine nucleotide metabolism caused by homozygous or compound heterozygous variants in the DPYD gene, which is located on chromosome 1p22 and containing 23 exons and is approximately 950 kb in length [79].