Errors of Inborn Metabolism (Ochronosis/Alkaptonuria) Flashcards
What is the basic problem of “Ochronosis”?
Congenital deficiency in the “Homogentisic Acid Oxidase” in the degration pathway of tyrosine. This enzyme is supposed to break down Homogenistic acid into methylacetoacetic acid, however since the enzyme is dysfunctional we have homogentistic acid accumulate.
What is the inheritance pattern of Ochronosis? When does it present?
It is autosomal recessive, and although the disease is present from birth, symptoms do not present until the 30s. It is termed “benign” as in not life threatening, however it is crippling.
What is the problem of having homogentisic acid accumulate in the body?
A large amount of homogentisic acid is excreted in urine and if left untreated it imparts a black color to urine due to oxidation.
Why is this disease called “ochronosis?”
The excess homogentisic acid binds to collagen in connective tissues, tendons and cartilage making them appear blue-black (ochronosis). This is most evidently seen in the cheeks nose and ears.
What is the most feared complication of ochronosis?
Accumilation of homogentisic acid in the articular cartilage, making the cartilage brittle and fibrillated, more prone to wear and tear damage and sometimes drives the pieces of cartilage into bone worsening the situation. Mimics osteoarthritis seen in the elderly but symptoms will present in the 30s.
What is the prime site of attack for ochronosis?
The vertebral column, specifically the intervertebral discs. Eventually progresses to the knees hips and shoulders, but small joints like hands and feet are spared.
What are the clinical findings of ochronosis?
Dark connectie tissues, brown pigmented sclera, urine turns black upon prolonged exposure to air, and symptoms of aarthralgias because of homogentisic acid toxicity to cartilage.
