Assertion: alkaptonuria's urine | /r/CapableOf | get stained
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text: The abnormality may be noticed when a child's napkins are noted to darken when urine gets stained, but occasionally passes unnoticed until the patient presents in middle or late life with back pain due to spinal ochronotic spondylosis and the characteristically densely calcified interver- tebral discs with relatively few other symptoms of degenerative arthritis.