Pathology

1. Melanin-like Pigments
ALKAPTONURIA
By Balkrishn Patel

2. This is a rare autosomal recessive disorder in
which there is deficiency of an oxidase
enzyme

3. required for break down of
homogentisic acid;

4. the latter then accumulates in the tissues and
is excreted in the urine (homogentisic
aciduria).

5. The urine of patients of alkaptonuria, if
allowed to stand for some hours in air, turns
black due to oxidation of homogentisic acid.

6. The pigment is melanin-like and is termed
ochronosis, first described by Virchow.
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7. It is deposited both intracellularly and intercellularly,
most often in the periarticular tissues such as cartilages,
capsules of joints, ligaments and tendons