HGD and alkaptonuria: Alkaptonuria (AKU) is an ultrarare disease, described by Archibald Garrod as the prototype for proving his theory of “inborn errors of metabolism” during his Croonian lectures of 1908.1, 2 AKU is characterized by the absence of functional homogentisate 1,2‐dioxygenase activity, the enzyme responsible for the breakdown of a tyrosine‐degradation product—homogentisic acid (HGA).3 The resulting accumulation of HGA is oxidized to a melanin‐like pigment in a process known as ochronosis which results in blue/black pigment in the eye, skin, and connective tissue, especially cartilage.