Oculocutaneous albinism (OCA) affects approximately 1/20,000 people worldwide. 
All forms of OCA exhibit generalized hypopigmentation. Reduced pigmentation 
during eye development results in misrouting of the optic nerves, nystagmus, 
alternating strabismus, and reduced visual acuity. Loss of pigmentation in the 
skin leads to an increased risk for skin cancer. Two common forms and one 
infrequent form of OCA have been described. OCA1 (MIM 203100) is associated with 
mutations of the TYR gene encoding tyrosinase (the rate-limiting enzyme in the 
production of melanin pigment) and accounts for approximately 40% of OCA 
worldwide. OCA2 (MIM 203200), the most common form of OCA, is associated with 
mutations of the P gene and accounts for approximately 50% of OCA worldwide. 
OCA3 (MIM 203290), a rare form of OCA and also known as "rufous/red albinism," 
is associated with mutations in TYRP1 (encoding tyrosinase-related protein 1). 
Analysis of the TYR and P genes in patients with OCA suggests that other genes 
may be associated with OCA. We have identified the mouse underwhite gene (uw) 
and its human orthologue, which underlies a new form of human OCA, termed 
"OCA4." The encoded protein, MATP (for "membrane-associated transporter 
protein") is predicted to span the membrane 12 times and likely functions as a 
transporter.