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Alkaptonuria (AKU)
Alkaptonuria is an inherited condition that causes urine to turn black when exposed to air. The three major features of alkaptonuria are the presence of dark urine, ochronosis, a buildup of dark pigment in connective tissues such as cartilage and skin, and arthritis of the spine and larger joints.
Prevalence
1 / 100,000
330–1,000
US Estimated
2,000–3,000
Europe Estimated
Age of Onset
Infancy
ICD-10
E70.2
Inheritance
Autosomal dominant
Autosomal recessive
Mitochondrial/Multigenic
X-linked dominant
X-linked recessive
5 Facts you should know
FACT
AKU is one of the original “inborn errors of metabolism.”
Archibald Garrod described it in 1902, making it the first genetic metabolic disorder recognized
FACT
Not just urine—connective tissues darken over time (ochronosis).
HGA polymerizes to form a bluish pigment deposited in cartilage, skin, sclera, and heart valves
FACT
Highly concentrated in Slovakia & the Dominican Republic.
Due to local founder mutations, incidence there can be as high as ~1 in 19,000
FACT
AKU leads to progressive arthropathy and joint destruction.
Spinal, hip, and knee arthritis often develop in patients by their 30s–40s, with severe symptoms later
FACT
First effective treatment came in 2020 with nitisinone.
Originally for tyrosinemia type I, it lowers HGA by ~99%, halting or reversing ochronosis; approved in Europe & UK
Interest over time
Google searches
Common signs & symptoms
Urine that darkens when exposed to air
Ochronosis
Joint pain and stiffness
Restricted chest expansion
Heart valve calcification
ligament ruptures
Current treatments
Nitisinone
lowers HGA by ~99%; slows disease progression, may reverse pigment deposit
Symptomatic care
pain relief (NSAIDs), physical therapy, joint replacement, stone management, valve surgery
Dietary restriction
low-protein (tyrosine/phenylalanine) diet with vitamin C—limited benefit