Think of alkaptonuria as a melanin-like substance in the urine and joints.
Presenting Symptoms
- Children: Dark Urine
- The presenting manifestation in children is typically urine that darkens when it sits for awhile (not common now with disposable diapers). The darkening occurs from the excess homogentisate in the urine (5,000 mg vs 20-30mg (normally).
- Adults: Joint Pain
- In adults, the disease presents, typically, from joint pain from the build-up of acetic acid in the tissues, which irritates the joints.
Pathogenesis
- It occurs from a deficiency in homogentisate 1,2 dioxygenase.
- This results in a build-up of a melanin-like polymer called benzoquinone acetic acid (a product of the oxidation of homogentisic acid), which binds connective tissue and causes dark pigmentation or ochronosis (arthritis).
- Thus, we can think of alkaptonuria as the opposite of albinism + the build-up of acetic acid in the tissues irritates the joints and causes joint pain.
References
- Calvo, Sherri; Collins, Heather; Greenberg, Kathleen, et. al at US National Library of Medicine, Genetics Home Reference. https://ghr.nlm.nih.gov