Autosomal Recessive Disorder Alkaptonuria

An 8-year-old boy is brought to his pediatrician for a school physical. His parents report that he is in good health. They are concerned, however,
because occasionally they find dark brown urine in the toilet when their son forgets to flush. Urinalysis is ordered; while his urine initially appears normal, it turns dark after standing. What is the Biochemical significance of the enzyme defective in this child?


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  1. Support

    This patient suffers from the autosomal recessive disorder alkaptonuria, a deficiency in homogentisic acid oxidase. This enzyme is responsible for degradation of tyrosine. As a result of the deficiency, there is an accumulation of alkapton bodies (homogentisic acid) in urine and cartilage. The lack of homogentisic oxidase blocks the metabolism of phenylalanine-tyrosine at the level of homogentisic acid. The homogentisic
    acid accumulates and a large amount is excreted, imparting a black color to the urine if allowed to stand and undergo oxidation. Dark spots can also be observed in the eyes of some patients. Affected patients are usually asymptomatic in childhood other than the change in urine color upon standing. In adulthood, the build-up of pigment in cartilage and its calcification can cause arthritic changes. By an unknown mechanism, the pigment causes the cartilage to lose its resiliency and become brittle and fibrillated. The arthropathy develops slowly and usually does not manifest until the patient is >30 years old. Although it is not life-threatening, it may be severely disabling

  2. okoro Roselyn chisom

    What’s autosomal. I’m a 100l student and need an answer

  3. okoro Roselyn chisom

    If gene B is an autosomal in inheritance while gene C is x- linked in animal species in which the female is XX and male is XY assuming a single dominant of gene B and C over their recessive alleles b& c respectively.
    What’s the genotype for a female who is Herero zygote for C&B.
    2. What’s genotype of a male who’s Herero zygote for gene B but carries gene C in the recessive

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