What Your Test Results Mean:

Carriers typically show no symptoms of hereditary thymine-uraciluria; however, carriers are at an increased risk of having a child with hereditary thymine-uraciluria. Risk for the current or future pregnancies is dependent on your partner’s carrier status. Carrier testing of your partner is recommended in addition to consultation with a genetic counselor.

Disease Explained:

Hereditary thymine-uraciluria is an inherited condition that prevents the body from breaking down the nucleotides thymine and uracil. This disease can vary drastically in severity: most affected individuals have no symptoms, while a few have mild to severe neurological problems that may include seizures, intellectual disability, delayed motor skills, and/or autism. Regardless of the individual’s symptoms, every affected person must avoid the chemotherapy drug 5-fluorouracil and other fluoropyrimidines. Because the body cannot break down these drugs, the fluoropyrimidines are toxic and life threatening to people with hereditary thymine-uraciluria. There is no cure or specific treatment for hereditary thymine-uraciluria, but symptoms such as seizures can be addressed as they arise.

How the Genetics Works:

Hereditary thymine-uraciluria is an autosomal recessive disorder caused by pathogenic variants in the DPYD gene. In general, individuals have two copies of the DPYD gene. Carriers of hereditary thymine-uraciluria have a single variant in one copy of the DPYD gene while individuals with hereditary thymine-uraciluria have variants in both copies of their genes, one inherited from each parent. Risk for two carriers to have a child with the disorder is 25%.