Oculocutaneous albinism (OCA) is the most common congenital disorder that causes generalized hypopigmentation.
The pigmentary dilution seen in OCA involves the skin, hair, and eyes.
Each of the four types of OCA is defined by a specific gene mutation that results in impaired biosynthesis of melanin.
Different OCA types can have distinctive pigmentation phenotypes.
Patients with albinism should receive cutaneous evaluation and counseling to help prevent and treat photodamage and skin cancer as well as ophthalmologic management for the visual manifestations of OCA.
Oculocutaneous albinism (OCA) is the most common congenital disorder that causes generalized hypopigmentation. The pigmentary dilution seen in OCA involves the skin, hair, and eyes. There are four types of OCA (OCA1, OCA2, OCA3, and OCA4), each of which is defined by a specific gene mutation that results in impaired biosynthesis of melanin. Table 50-1 summarizes the characteristic features of each OCA type.
TABLE 50-1Characteristics of oculocutaneous albinism (OCA), types 1A, 1B, 2, 3, and 4 |Favorite Table|Download (.pdf) TABLE 50-1 Characteristics of oculocutaneous albinism (OCA), types 1A, 1B, 2, 3, and 4
| ||OCA1A ||OCA1B ||OCA2 ||OCA3 ||OCA4 |
|Important subtypes || ||Temperature-sensitive OCA1B ||Brown OCA ||Rufous OCA || |
|Gene mutation ||TYR ||TYR (leaky mutation) ||OCA2 (P gene) ||TYRP1 ||SLC45A2 (MATP, AIM1) |
|Protein product ||Tyrosinase ||Tyrosinase ||OCA2 (P protein) ||Tyrosinase-related protein 1 ||Solute carrier family 45 member 2 (membrane-associated transporter protein, absent in melanoma 1 protein) |
|Chromosome ||11q14.3 ||11q14.3 ||15q11.2-q12 ||9p23 ||5p13.3 |
|Hair color ||White ||Minimal to no pigment at birth, yellow/blonde to brown with age ||Yellow (may be blonde or red in Caucasians, light brown in brown OCA) ||Ginger-red (rufous type), mild hypopigmentation (nonrufous) ||Minimal to near-normal pigmentation |
|Skin color ||White (with amelanotic pink melanocytic nevi) ||Minimal to no pigment at birth, may darken with age ||Creamy white (light brown in brown OCA) ||Red-bronze (rufous type), mild hypopigmentation (nonrufous) || |
|Iris color ||Pink or blue-gray || ||Blue-gray to brown ||Blue-gray to brown || |
This chapter describes the epidemiology, pathogenesis, and clinical features of each of the four types of OCA. Management of OCA, nitisinone as a possible OCA treatment, the historical anthropology of OCA, and the contemporary struggles of East Africans with OCA are also discussed.
OCA has an estimated frequency of approximately 1 in 17,000 to 20,000 in the general population.1,2,3 Although four types of OCA have been described, the vast majority of known OCA cases are OCA1 (40%) or OCA2 (50%).3 The frequencies of different forms of OCA have wide racial and geographic variation. OCA2 is more common in darker skin of color individuals; whereas the overall prevalence of OCA2 is only 1 in 36,000 in the United States, it is 1 in 10,000 in African Americans.4 A much higher OCA2 prevalence of 1 ...