Alkaptonuria is a rare inherited disorder characterized by the accumulation of a substance called homogentisic acid (HGA) in the body. The condition is caused by a defect in the enzyme homogentisate 1,2-dioxygenase (HGD), which is responsible for breaking down HGA.
Normally, HGA is produced as a byproduct during the breakdown of certain amino acids, particularly phenylalanine and tyrosine, which are obtained from the diet. In individuals with alkaptonuria, the HGD enzyme is defective or absent, leading to the accumulation of HGA in the body.
The excess HGA is excreted in the urine, causing it to turn dark brown or black when exposed to air. This is one of the characteristic signs of alkaptonuria. HGA can also accumulate in other tissues, such as cartilage and connective tissues, leading to additional symptoms, including joint problems and darkening of the skin and whites of the eyes.
Alkaptonuria is an autosomal recessive disorder, which means that an affected individual inherits two copies of the defective gene, one from each parent. Carriers of a single copy of the gene do not typically show symptoms of the condition.
It’s worth noting that alkaptonuria is a genetic disorder, and the underlying cause is a mutation in the HGD gene. However, the specific factors that contribute to the development of this mutation are not fully understood.
