Alkaptonuria, a metabolic disorder characterized by a triad of homogentisic 
aciduria, arthritis and ochronosis is one of the first conditions in the charter 
of group of inborn errors of metabolism proposed to have Mendelian recessive 
inheritance. It is due to the deficiency of the enzyme homogentisic acid oxidase 
which catalyzes the conversion of homogentisic acid to maleylacetoacetic acid in 
the catabolism of tyrosine. Homogentisic acid thus accumulates in cells and body 
fluids and its oxidized polymers bind to collagen, leading to progressive 
deposition of grey to bluish black pigment resulting in degenerative changes in 
cartilage, intervertebral disc and other connective tissues, leading to 
arthritis which is the only disabling effect in an affected older individual. 
However the diagnosis can be made in neonates when blackish stain is noticed in 
an unwashed diaper. Alkaptonuria is treated symptomatically, surgical 
intervention necessitates in advanced stages, treatment with ascorbic acid 
(Vitamin C) and dietary restrictions of food containing phenylalanine and 
tyrosine have proved to be successful in alleviating the symptoms.