Dihydropyrimidine dehydrogenase (DPD) deficiency is a disorder characterized by a wide range of phenotypic variability that range from no symptoms to a severe neurological involvement. A severely affected patients show epilepsy, intellectual disability, hypertonia and have microcephaly. The disease prevalence is unknown. Patients with DPD deficiency including those who do not show the signs of the disease are vulnerable to life-threatening toxic reactions to certain drugs called fluoropyrimidines that are used to treat cancer. Diagnosis can be done my measuring the level of uracil and thiamin, which are usually increased in affected patients along with genetic testing.