Alkaptonuria

- rare (1:200,000) disorder of tyrosine metabolism
- autosomal recessive
- deficiency of homogentisic acid oxidase
- leads to excretion of large amount of homogentisic acid in urine and accumulation of oxidised homogentisic acid pigment in connective tissues (ochronosis)
- presents with dark urine, foci of gray-brown scleral pigment, darkening of concha, anthelic and helix of ear
- ochronotic arthritis is heralded by pain, stiffness and some limitation of motion of hips, knees and shoulders
- interverterbral disc calcification is characteristic of alkaptonuria and is seen on spinal X rays
- degenerative cardiovascular disease is increased in older patients
- treatment: Nitisinone