Accumulation of homogentisic acid causes:

Ochronosis REF: Clinical Paediatric Dermatology by Thappa - Page 156, Differential diagnosis in internal medicine: from symptom to diagnosis - Page 347, http://en.wikipedia.org/wiki/Ochronosis, http://en.wikipedia.org/wiki/Alkaptonuria Repeat from June 2010 Ochronosis is the syndrome caused by the accumulation of homogentisic acid in connective tissues. The condition was named after the yellowish (ocher-like) discoloration of the tissue seen on microscopic examination. However, macroscopically the affected tissues appear bluish grey because of a light scattering phenomenon known as the Tyndall effect. The condition is most often associated with alkaptonuria but can occur from exogenous administration of phenol complexes like hydroquinone. Alkaptonuria (black urine disease or alcaptonuria) is a rare inherited genetic disorder of phenylalanine and tyrosine metabolism. This is an autosomal recessive condition that is due to a defect in the enzyme homogentisate 1, 2-dioxygenase, which paicipates in the degradation of tyrosine. As a result, a toxic tyrosine byproduct called homogentisic acid (or alkapton) accumulates in the blood and is excreted in urine in large amounts (hence -uria)