Figure 4. Spectrum of pigmentation associated with tyrosinase mutations having different amounts of residual enzymatic activity.

The majority of mutations in the tyrosinase gene associated with OCA1 cause a complete lack of tyrosinase activity resulting in the absence of all cutaneous and ocular pigment. A small percentage of mutations result in some residual enzymatic activity allowing pigment to form, but still retaining the ocular abnormalities associated with OCA. We know that individuals heterozygous for tyrosinase mutations, having 50% of normal tyrosinase activity, have normal vision, but we do not know how much tyrosinase activity (pigment formation) must be present for correct ocular development.