Alkaptonuria (AKU) was the first condition noted as following Mendelian Inheritance by Sir Archibald Garrod in 1902. Since then, more work has been done to understand its genetic mechanism. AKU is now understood to be a recessive disorder, caused by a single gene defect. It is mapped to Chromosome 3 between regions 3q21-q23, the site of the homogentisate 1,2-dioxygenase (HGD) gene.