An Overview of Alkaptonuria
Alkaptonuria is a rare genetic metabolic disorder that affects how the body breaks down two specific amino acids — tyrosine and phenylalanine. It occurs due to a mutation in the HGD gene, which leads to a deficiency in an enzyme called homogentisate 1,2-dioxygenase. Without this enzyme, a substance called homogentisic acid (HGA) builds up in the body.
Excess HGA Accumalations
Over time, excess HGA accumulates in connective tissues such as cartilage, tendons, and skin — a process known as ochronosis. This causes these tissues to darken and become brittle, eventually leading to joint pain, arthritis, and other complications. The condition also causes urine to darken when left standing, often the first noticeable sign in infancy.
Though alkaptonuria is rare globally, its symptoms can have a major impact on quality of life. It is inherited in an autosomal recessive pattern, meaning both parents must carry the defective gene for a child to develop the condition. Carriers usually show no symptoms.
Hidden in Age
In South Africa, as in many parts of the world, diagnosis may be delayed due to its rarity. Many people are not diagnosed until adulthood, when joint pain or spinal stiffness begins. There is no known cure, but early recognition, lifestyle adjustments, and supportive care can significantly slow progression and improve comfort.
In the next section, we’ll explore the causes and genetics of alkaptonuria in more detail.
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