Oculocutaneous albinism

Abstract

Oculocutaneous albinism (OCA) is a group of inherited disorders of melanin biosynthesis characterized by a generalized reduction in pigmentation of hair, skin and eyes. The prevalence of all forms of albinism varies considerably worldwide and has been estimated at approximately 1/ 17,000, suggesting that about 1 in 70 people carry a gene for OCA. The clinical spectrum of OCA ranges, with OCA1A being the most severe type with a complete lack of melanin production throughout life, while the milder forms OCA1B, OCA2, OCA3 and OCA4 show some pigment accumulation over time. Clinical manifestations include various degrees of congenital nystagmus, iris hypopigmentation and translucency, reduced pigmentation of the retinal pigment epithelium, foveal hypoplasia, reduced visual acuity usually (20/60 to 20/400) and refractive errors, color vision impairment and prominent photophobia. Misrouting of the optic nerves is a characteristic finding, resulting in strabismus and reduced stereoscopic vision. The degree of skin and hair hypopigmentation varies with the type of OCA. The incidence of skin cancer may be increased. All four types of OCA are inherited as autosomal recessive disorders. At least four genes are responsible for the different types of the disease (TYR, OCA2, TYRP1 and MATP). Diagnosis is based on clinical findings of hypopigmentation of the skin and hair, in addition to the characteristic ocular symptoms. Due to the clinical overlap between the OCA forms, molecular diagnosis is necessary to establish the gene defect and OCA subtype. Molecular genetic testing of TYR and OCA2 is available on a clinical basis, while, at present, analysis of TYRP1 and MATP is on research basis only. Differential diagnosis includes ocular albinism, Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, Griscelli syndrome, and Waardenburg syndrome type II. Carrier detection and prenatal diagnosis are possible when the disease causing mutations have been identified in the family. Glasses (possibly bifocals) and dark glasses or photocromic lenses may offer sufficient help for reduced visual activity and photophobia. Correction of strabismus and nystagmus is necessary and sunscreens are recommended. Regular skin checks for early detection of skin cancer should be offered. Persons with OCA have normal lifespan, development, intelligence and fertility. Disease name Oculocutaneous albinism DefinitionOculocutaneous albinism (OCA) is a group of four autosomal recessive disorders caused by either a complete lack or a reduction of melanin biosynthesis in the melanocytes

Case report: a black and white twin

“…As functional tyrosinase is produced in OCA type 2, it is named the tyrosinase-positive form. 5,6 OCA types 1 and 2 differ on the bases of genetics and the degree of skin and hair hypopigmentation and ocular manifestations, with OCA type 1 being more severe.…”

“…Foveal hypoplasia leads to an inaccurate projection of the image on the macula lutea because of the widespread localization of the cones, resulting in reduced vision and nystagmus that presents from the age of 3 to 4 months. 5,6 There is no curative treatment for albinism. Photoprotection, however, can reduce the main complications such as skin cancer and loss of vision.…”

“…Complaints of nystagmus can be treated with contacts or surgical correction of the eye muscles. 5,6 The most prevalent skin disorders in albinos are basal cell carcinoma and squamous cell carcinoma, whereas melanoma are rare. 5 The highest prevalence of squamous cell carcinoma is consistently shown in the albino population.…”

Clinical utility gene card for: Oculocutaneous albinism

“…In cases with novel mutations family studies of both affected and non-affected can be helpful. References for frequencies can be found in Gronskov et al 13 Mutations in C10orf11 have been found in OCA individuals from the Faroe Islands and in an OCA individual from Lithuania. 9 Mutations in SLC24A5 have been found in OCA individuals from India and China.…”

Foveal Hypoplasia in Oculocutaneous Albinism and the Role of OCT

“…Clinical manifestations may include reduced visual acuity, refractive errors, colour vision defects, photophobia, nystagmus, iris transillumination, reduced retinal pigment, foveal hypoplasia and abnormal chiasmal decussation [1,2]. Earlier onset of nystagmus correlates with degree of foveal hypoplasia.…”