Alkaptonuria is an inherited genetic disorder caused by the deficiency of an enzyme called homogentisic acid oxidase (HGO). This enzyme is responsible for breaking down the amino acid tyrosine, which is found in proteins in the human body. When the enzyme is not present, the tyrosine accumulates in the body and is then converted into a chemical called homogentisic acid (HGA). This acid is then excreted through the urine, turning it a dark brown or black color, which is the primary symptom of alkaptonuria.
The gene for HGO is located on chromosome 3 and is inherited as an autosomal recessive trait, meaning that both the mother and the father must pass on the defective gene in order for a person to have the disorder. If both parents are carriers of the mutated gene, there is a 25% chance that their child will have the disorder.
Alkaptonuria can cause a wide range of complications, depending on the severity of the disorder. Symptoms can range from mild joint pain and stiffness, to kidney stones, and even heart problems. If left untreated, it can lead to serious health problems such as arthritis, osteoarthritis, and even heart failure. Treatment typically involves medications that can reduce the severity of the symptoms, as well as lifestyle modifications that can help prevent further complications.