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enzyme defct

1.7K views 6 replies 6 participants last post by  ricko335  
#1 ·
A child with white hair, very pale skin, and blue eyes undergoes an ophthalmologic evaluation and is diagnosed with strabismus and 20/400 vision. The patient is otherwise healthy and demonstrates no evidence of neurologic defects. To account for these findings, which enzyme could be defective?
A. Cystathionine synthetase
B. Tyrosine hydroxylase
C. Homogentisic acid dioxygenase
D. Tyrosinase
E. Phenylalanine hydroxylase
 
#7 ·
The correct answer is D.
This child has oculocutaneous albinism, which is most classically due to tyrosinase deficiency. While both tyrosinase and tyrosine hydroxylase produce L-DOPA, which is a precursor for melanin, it is tyrosinase that moves Tyr into the melanin pathway by further converting L-DOPA to DOPA-oxidase (a second reaction).