Oculocutaneous Albinism Type 4

Excerpt

Clinical characteristics: Oculocutaneous albinism type 4 (OCA4) is characterized by: (1) the ocular changes found in all types of albinism that include 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 that depends on the amount of iris and retinal pigment; and misrouting of the optic nerves at the chiasm associated with alternating strabismus, reduced stereoscopic vision, and altered visual evoked potential; and (2) reduced pigmentation of the skin and hair that ranges from minimal to near normal. Infants with OCA4 are usually recognized by age one year due to hypopigmentation of the skin and hair that ranges in color from silvery white to light yellow. Although hair color may darken with time, it does not vary significantly from childhood to adulthood.

Diagnosis/testing: The diagnosis of OCA4 is established in a proband with suggestive findings and biallelic pathogenic variants in SLC45A2 identified by molecular genetic testing.

Management: Treatment of manifestations: Correction of refractive errors with spectacles or contact lenses to improve visual acuity. Strabismus surgery may be considered for cosmetic reasons. Although dark glasses may reduce photophobia, they may also reduce vision; thus, a hat with a brim or visor is best to reduce photophobia. Protection from the sun by wearing protective clothing and regular application of topical sunscreens is essential to prevent sunburn and secondary skin changes, and to decrease the risk of skin cancer later in life. Individuals with OCA4 should stay out of the sun from an early age, because cumulative ultraviolet exposure is a major risk factor for skin cancers.

Surveillance: Annual ophthalmologic examination and reassessment for accurate correction of refractive error. Evaluation of the skin for cancer screening every six months is recommended.

Agents/circumstances to avoid: Prolonged exposure of the skin to the sun, activities without appropriate eye protection from the sun, and tanning beds and artificial ultraviolet sources.

Genetic counseling: OCA4 is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an SLC45A2 pathogenic variant, each sib of an affected individual has at conception 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. Once the SLC45A2 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal/preimplantation genetic testing are possible.