Why does Alkaptonuria happen?
Last updated September 7, 2026.
**Alkaptonuria happens when you inherit changes in both copies of the HGD gene, leaving your body unable to properly break down homogentisic acid.** This acid forms as your body breaks down the protein building blocks tyrosine and phenylalanine. You usually inherit one altered gene copy from each parent, who can carry it without symptoms. The acid can make your urine darken after exposure to air and gradually cause pigment deposits and joint problems. Your eating habits do not cause this inherited condition. If you have symptoms or a family history, discuss testing with your clinician and get guidance before restricting protein.
What to do
- **Get urine changes checked:** Tell your clinician if your urine becomes brown or black after standing.
- **Share your family history:** Mention relatives with alkaptonuria when discussing testing with your clinician.
- **Ask about genetic counseling:** If alkaptonuria runs in your family, discuss inheritance and testing before planning a pregnancy.
- **Get dietary guidance:** Work with your clinician or dietitian before reducing protein.