Chapter 11, Problem 13TYU

Summary Introduction

Alkaptonuria is an autosomal recessive genetic disorder. The mutation in the HGD gene encoding homogentisate 1,2-dioxygenase enzyme causes alkaptonuria. This enzyme is involved in the breakdown of homogentisic acid (HGA). The mutation in the HGD leads to the accumulation of HGA, which serves as an intermediate in the pathway of tyrosine degradation. Therefore, in this genetic disorder tyrosine is not processed. HGA and alkapton (the oxidized form of HGA) are excreted in the urine with dark color. This is because alkapton is not metabolized in this disorder.