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NBME 21 Answers
A 5-year-old boy is brought to the physician for a ...
Lack of choroidal pigment deposition in the macula
i don't understand this at all. i am completely blank...please help
@temmy. This question tests our knowledge on albinism which is normally a tyrosinase deficiency disease but the vignette states that the boy's albinism is caused by a genetic mutation in the TYRP1 gene which is shown in the biochemical pathway. A gene that helps in the synthesis of Eumelanin.
Now you have to understand that all precursors before that gene is the pathway would still be available if not increased which make 2 of the options in the question wrong.
you also have to understand this:
(Eu)melanin = (normo)melanin i.e normal melanin which is protective to the skin, decreases reactive oxygen species and gives the dark pigments to the iris, choroid, skin, hair e.t.c.
(feo)melanin = (fake)melanin i.e pheomelanin, the one present in our patient here which is less protective again the uv rays, cannot pigment and cannot decrease ROS generated in the skin.
i hope this helps
@henoch280 thank u very much! I got it right by luck but now i do understand :D