Rs3918290

23andMe reports that the A allele of rs3918290 is associated with the rare recessive disorder dihydropyrimidine dehydrogenase deficiency (DPD), also known as hereditary thymine-uraciluria or familial pyrimidinemia.

Note that the terms used in the literature for this gene can be confusing, since the gene is in reverse orientation to the chromosome strand on the reference genome.

pharmgkb - defines *2A allele, which has a significantly higher chance of 5-fluorouracil toxicity

Fluorouracil Toxicity