Arthropathia ochronotica

Abstract

: Alkaptonuria (AKU) is a rare autosomal recessive metabolic disease caused by a disorder of phenylalanine and tyrosine metabolism, resulting in accumulation and deposition of homogentisic acid (HGA) in the body. This deposition further causes progressive functional disorders in different organ systems, with the locomotor system being the most affected one. A specific triad of symptoms occurs in patients suffering from AKU: 1. at birth, a change of urine color is present when urine is exposed to air, 2. occurrence of dark pigmentations in connective tissues becomes visible over time, 3. complications of the locomotor, urogenital and cardiovascular systems present gradually. Arthropathia ochronotica occurs in patients suffering from AKU due to precipitation and deposition of HGA in the joint tissue (cartilage, tendons, ligaments, menisci, etc.). The accumulation can be seen as small foci of blue-black pigmentations. HGA deposits in collagen fibers, causing tendons and ligaments thickening. This causes them to be less resistant to mechanical forces, resulting in frequent ruptures caused by minimal trauma. Also, the deposition facilitates cartilage degeneration, often requiring an operative treatment. The knees are the most commonly affected joints, while changes can be seen in the spine and other large joints. As there is no specific treatment, alleviation of symptoms is the only treatment option. It has the goal of increasing individual functionality and quality of life. As an option for end-stage treatment, joint replacement surgery proved to be effective. In the future, an enzyme replacement therapy or gene therapy may be developed to treat AKU successfully.