Three-generational alkaptonuria in a non-consanguineous family

ARTHROPLASTY IN ALKAPTONURIC OCHRONOSIS

Ochronotic degenerative arthropathy occurs in patients with alkaptonuria. Alkaptonuria disorder is an extremely rare disease characterized by black pigmentation of various tissues (e.g., cartilage and connective tissue). Ochronotic arthropathy is a disabling disease that primarily affects the large joints. Like other metabolic diseases that involve the musculoskeletal system, care must be taken with regard to the quality of the affected bones, tendons and ligaments, and therefore the stability and survival of joint prosthesis. The following is a report of a 66-year-old man affected by several musculoskeletal manifestations of alkaptonuria with severe joints disruption, who was successfully treated with total left hip and total right knee replacements. Surgical, anesthesiological and postoperative management of these patients may require more vigilance due to the associated comorbidities of this disorder.

Oxidative stress and mechanisms of ochronosis in alkaptonuria

Alkaptonuria (AKU) is a rare metabolic disease due to a deficient activity of the enzyme homogentisate 1,2-dioxygenase (HGD), involved in Phe and Tyr catabolism. Due to such a deficiency, AKU patients undergo accumulation of the metabolite homogentisic acid (HGA), which is prone to oxidation/polymerization reactions causing the production of a melanin-like pigment. Once the pigment is deposited onto connective tissues (mainly in joints, spine, and cardiac valves), a classical bluish-brown discoloration is imparted, leading to a phenomenon known as "ochronosis", the hallmark of AKU. A clarification of the molecular mechanisms for the production and deposition of the ochronotic pigment in AKU started only recently with a range of in vitro and ex vivo human models used for the study of HGA-induced effects. Thanks to redox-proteomic analyses, it was found that HGA could induce significant oxidation of a number of serum and chondrocyte proteins. Further investigations allowed highlighting how HGA-induced proteome alteration, lipid peroxidation, thiol depletion, and amyloid production could contribute to oxidative stress generation and protein oxidation in AKU. This review briefly summarizes the most recent findings on HGA-induced oxidative stress in AKU, helping in the clarification of the molecular mechanisms of ochronosis and potentially providing the basis for its pharmacological treatment. Future work should be undertaken in order to validate in vivo the results so far obtained in in vitro AKU models.

Alkaptonuria, more than just a mere disease

Alkaptonuria (AKU) is considered a rare autosomal recessive condition that results in an accumulation of homogentisic acid in body tissues and causes long-term clinical, neurological and psychological complications. We present a comprehensive evaluation of an atypical 46-year-old Caucasian male who developed all clinical diagnostic symptoms of AKU (ochronotic pigmentations, dark urine and clinical arthritis of major joints including spine) by 25 years of age, well before the typical age mentioned in many reviews. First signs of ochronotic ear pigmentations unexpectedly started appearing as early as 12 years of age. A long “disease-free” period typical in classical AKU patient was also absent. This case report highlights the importance of considering psychological issues in AKU patients. The patient showed symptoms of dysthymia reporting social isolation, diminished interest in pleasurable activities, feeling of worthlessness and irritability as major psychological issues. Early ochronotic pigmentation, advanced spinal myelopathy and arthropathy of major joints suggests aggressive course of the disease. Our patient underwent bilateral shoulder replacement due to AKU-induced arthropathy resulting in restoration of some range of motions. AKU is not fully understood and we recommend treating it as a multidimensional disease with simultaneous physiological, neurological and psychological effects. Early diagnosis, understanding of disease prognosis and emphasis on psychological health is needed to improve the quality of life of AKU patients.

An update on molecular genetics of Alkaptonuria (AKU)

Alkaptonuria (AKU) is an autosomal recessive disorder caused by a deficiency of homogentisate 1,2 dioxygenase (HGD) and characterized by homogentisic aciduria, ochronosis, and ochronotic arthritis. The defect is caused by mutations in the HGD gene, which maps to the human chromosome 3q21-q23. AKU shows a very low prevalence (1:100,000-250,000) in most ethnic groups, but there are countries such as Slovakia and the Dominican Republic in which the incidence of this disorder rises to as much as 1:19,000. In this work, we summarize the genetic aspects of AKU in general and the distribution of all known disease-causing mutations reported so far. We focus on special features of AKU in Slovakia, which is one of the countries with an increased incidence of this rare metabolic disorder.