Accomulation of homogentisic acid and its oxidation product (benzoquinone acetic acid)
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Etiology
- Autossomal recessive mutation in HGD gene
- Lack of functional homogentisic acid dioxygenase → impaired conversion of homogentisic acid to 4-maleylacetoacetate (phenylalanine and tyrosine metabolism)
- Accumulation of homogentisic acid → tissue discoloration and organ damage
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Clinical presentation
- Skin: ochronosis
- dark colored urine after urination, gray blue pigmentation of the sclera and helic, as well as, the palms, soles, genital and axillary regions → ochronosis and arthropathy
- Symptoms appear after 20yo
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