HGD and alkaptonuria: Black urine disease also known as alkaptonuria is a rare autosomal recessive inborn error of metabolism as defined in 1902 [1]. The defect lies in the catabolism of tyrosine and the deficiency of the homogentisate 1,2-dioxygenase (HGO) enzyme, which is responsible for the formation of homogentisic acid that is, upon contact with air, converted to a pigment polymer that causes the blackish discoloration of the standing urine [2].