Oculocutaneous Albinism Type 2 – RETIRED CHAPTER, FOR HISTORICAL REFERENCE ONLY

Review
In: GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993–2021.
[updated ].

Excerpt

NOTE: THIS PUBLICATION HAS BEEN RETIRED. THIS ARCHIVAL VERSION IS FOR HISTORICAL REFERENCE ONLY, AND THE INFORMATION MAY BE OUT OF DATE.

Clinical characteristics: Oculocutaneous albinism type 2 (OCA2) is characterized by hypopigmentation of the skin and hair and the characteristic ocular changes found in all types of albinism, including nystagmus; reduced iris pigment with iris translucency; reduced retinal pigment with visualization of the choroidal blood vessels on ophthalmoscopic examination; foveal hypoplasia associated with reduction in visual acuity; and misrouting of the optic nerve fiber radiations at the chiasm, associated with strabismus, reduced stereoscopic vision, and altered visual evoked potentials (VEP). Individuals with OCA2 are usually recognized within the first three to six months of life because of the ocular features of visual inattention, nystagmus, and strabismus. Vision is stable to slowly improving after early childhood until mid- to late teens, and no major change or loss of established visual acuity occurs related to the albinism. The amount of cutaneous pigmentation in OCA2 ranges from minimal to near-normal compared to others of the same ethnic and family backgrounds. Newborns with OCA2 almost always have lightly pigmented hair, brows, and lashes, with color ranging from light yellow to blond to brown. Hair color may darken with age but does not vary substantially from adolescence to adulthood. Brown OCA, initially identified in Africans and African Americans with light brown hair and skin, is part of the spectrum of OCA2.

Diagnosis/testing: The diagnosis of OCA2 is based on clinical findings. OCA2 (previously called P) is the only gene in which pathogenic variants are known to cause oculocutaneous albinism type 2.

Management: Treatment of manifestations: Correction of refractive errors with spectacles or (when age-appropriate) contact lenses may improve visual acuity; strabismus surgery can be considered for either functional (improved peripheral fusion) or cosmetic reasons. Hats with brims and dark glasses or transition lenses often reduce discomfort in bright light (photodysphoria).

Protection from sun exposure with appropriate skin-covering clothing and sunscreens prevents burning, consequent skin damage, and the enhanced risk of skin cancer. Skin cancer, including a slightly enhanced risk for cutaneous melanoma, is treated as for the general population.

Surveillance: Annual ophthalmologic examination to reassess refractive errors, strabismus and/or face turn; annual to biennial skin examination for evidence of sun-related skin damage and/or precancerous or cancerous lesions.

Agents/circumstances to avoid: Prolonged sun exposure.

Genetic counseling: OCA2 is inherited in an autosomal recessive manner. The parents of a proband are obligate heterozygotes and therefore carry one mutated allele. Heterozygotes (carriers) are asymptomatic. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives and prenatal testing for a pregnancy at increased risk are possible if the pathogenic variants in an affected family member are known.

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