The earliest manifestation of Alkaptonuria is -
Ochronosis (Alkaptonuria)

Alkaptonuria is a rare, heritable disorder characterized by the appearance of homogentisic acid in the urine, dark pigmentation of the connective tissues (ochronosis) and calcification of hyaline and fibrocartilage.
The inborn error is an absence of homogentisic acid oxidase in the liver and kidney. Those affected usually remain asymptomatic until the 3rd & 4th decade when they present with pain and stiffness of the spine & (later) larger joints.
Dark pigmentation of ear cartilage & sclera and staining of clothes by homogentisic acid in sweat. Urine turns dark brown when it is alkalinized or if it is left to stand for some hours.
X-ray reveal narrowing & calcification of intervertebral discs. Peripheral joints show chondrocalcinosis & severe osteoarthritis.
Ankylosis of lumbodorsal spine
Ochronotic arthritis
Prostatic calculi
Pigmentation of tympanic membrane