MITF and microphthalmia: In the total absence of functional Mitf, as seen in mice homozygous for the Mitfmi-vga9 allele, mice exhibit microphthalmia and have neither pigmented RPE cells nor pigmented neural crest–derived cells in skin, iris, choroid, inner ear, or heart.3 Nevertheless, there is a fundamental difference in the way these two types of pigment cells respond to Mitf loss-of-function mutations.