@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. while (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

Proccess of elimination for this one. Two you can eliminate immediately just from looking at the biochemical pathway chart. The other two required knowledge that eumelanin is more protective than pheomelanin (this is why redheads burn more easily). Because pheomelanin is less protective, there would be more not less ROS from sunlight.

I believe this one was just an answer of exclusion / process of elimination. You had to understand that the photoprotective form of melanin is the black one (eumelanin) and phytomelanin (red) is less photoprotective. From there it basically is saying a complete loss of function mutation of TYRP1.

• Absence of tyrosinase (choice A) is eliminated—tyrosinase is way upstream of TRYP1.

• Decreased concentrations of 5,6 (choice B) is eliminated since there would be increased substrate of TRYP1.

• Decreased ROS (choice C) and increased photoprotection (choice D) are eliminated because there is less photoprotection from the loss of eumelanin = increased ROS.

Apparently choroidal pigment is made of phytomelanin but no way you were expected to know that.

Eumelanin also helps the choroid limit uncontrolled reflection within the eye that would potentially result in the perception of confusing image

I cut open an eyeball once and I was surprised how dense black the material inside was. That plus process of elimination brought me to the right answer