RESUMO
Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disorder that shows large phenotypical variability, ranging from no symptoms to intellectual disability, motor retardation, and convulsions. In addition, homozygous and heterozygous mutation carriers can develop severe 5‑fluorouracil (5‑FU) toxicity. The lack of genotype‑phenotype correlation and the possibility of other factors playing a role in the manifestation of the neurological abnormalities, make the management and education of asymptomatic DPD individuals more challenging. We describe a 3‑month‑old baby who was incidentally found by urine organic acid testing (done as part of positive newborn screen) to have very high level of thymine and uracil, consistent with DPD deficiency. Since the prevalence of asymptomatic DPD deficiency in the general population is fairly significant (1 in 10,000), we emphasize in this case study the importance of developing a guideline in genetic counseling and patient education for this condition as well as other incidental laboratory findings.