Mutation of the tyrosinase gene (TYR) causes oculocutaneous albinism, type 1 
(OCA1), a condition characterized by reduced skin and eye melanin pigmentation 
and by vision loss. The retinal pigment epithelium influences postnatal visual 
development. Therefore, increasing ocular pigmentation in patients with OCA1 
might enhance visual function. There are 2 forms of OCA1, OCA-1A and OCA-1B. 
Individuals with the former lack functional tyrosinase and therefore lack 
melanin, while individuals with the latter produce some melanin. We hypothesized 
that increasing plasma tyrosine concentrations using nitisinone, an FDA-approved 
inhibitor of tyrosine degradation, could stabilize tyrosinase and improve 
pigmentation in individuals with OCA1. Here, we tested this hypothesis in mice 
homozygous for either the Tyrc-2J null allele or the Tyrc-h allele, which model 
OCA-1A and OCA-1B, respectively. Only nitisinone-treated Tyrc-h/c-h mice 
manifested increased pigmentation in their fur and irides and had more pigmented 
melanosomes. High levels of tyrosine improved the stability and enzymatic 
function of the Tyrc-h protein and also increased overall melanin levels in 
melanocytes from a human with OCA-1B. These results suggest that the use of 
nitisinone in OCA-1B patients could improve their pigmentation and potentially 
ameliorate vision loss.