brown oculocutaneous albinism

Albinism, Oculocutaneous, Type III

Clinical Characteristics
Ocular Features: 

The irides may be multicolored with the central potion light brown and the peripheral areas blue-gray.  Translucency of a punctate and radial nature is present.  Nystagmus is present in almost all cases and strabismus is present in nearly half.  Visual acuity is in the range of 20/60 to 20/200.   Photophobia is less severe than in other types of oculocutaneous albinism, possibly because the vast majority of individuals (86%) have some pigmentation in the fundus. 

Systemic Features: 

The hair in dark-skinned people may be medium brown while the skin is often light brown and subject to faint tanning.  However, the hair is often copper-red in color which has given rise to the designation rufous oculocutaneous albinism. 

Genetics

This tyrosinase-positive type of albinism is sometimes called 'rufous' (ROCA) or 'brown' (BOCA) oculocutaneous albinism and is frequently found in dark-skinned individual such as Africans, African-Americans, and Hispanics.  Like other types it is inherited in an autosomal recessive pattern.  Mutations in the tyrosinase-related protein-1, TYRP1 (9p23), are responsible which seems to lead to an arrest in melanin maturation and a decrease in the amount of insoluble melanin in melanocytes.

Other autosomal recessive types of oculocutaneous albinism are: OCA1 (203100, 606952), OCA2 (203200), and OCA4 (606574). 

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available for the hypopigmentation.  However, precautions against excessive sun exposure are advised.  Low vision aids can be helpful. 

References
Article Title: 

Oculocutaneous albinism

Gronskov K, Ek J, Brondum-Nielsen K. Oculocutaneous albinism. Orphanet J Rare Dis. 2007 Nov 2;2:43. Review.

PubMed ID: 
17980020

Albinism, Oculocutaneous, Type II

Clinical Characteristics
Ocular Features: 

The iris and retina lack normal pigmentation and translucency of the iris can be demonstrated.  Anomalous decussation of neuronal axons in the chiasm and foveal hypoplasia result in decreased visual acuity.  Vision loss into the range of 20/100-20/200 does not progress after early childhood but is sometimes as good as 20/30.   Nystagmus is often present from about 3-4 months of age although it is less severe than in type I oculocutaneous albinism (203100, 606952).  The iris may darken to some extent with age.  Strabismus has been reported.  Significant refractive errors are often present and stereopsis is reduced.  The VEP responses are altered and can be used to document abnormal chiasmal decussation. 

Systemic Features: 

Melanin pigment is reduced in the skin and hair as well as the eyes.  Individuals at birth may be misdiagnosed as OCA type I but it is common for pigmentation to increase in older individuals resulting in yellow or reddish-blond hair and the appearance of freckles and nevi.  The skin may be creamy-white but this is often not as striking as in OCAI.  It is possible for tanning to take place in some patients.  This condition in Africans or African Americans is sometimes called brown oculocutaneous albinism (BOCA).  There is an increased risk of skin cancer of all types. 

Genetics

Type II is the most common type of oculocutaneous albinism and is especially prevalent among individuals of African heritage and in several Native American populations.  It is an autosomal recessive condition caused by homozygous 2.7 kb deletions in the OCA2 gene (15q24.3-q12).  Heterozygotes have normal pigmentation. 

Oculocutaneous albinism type I (203100, 606952) is a separate disorder with many similar features caused by mutations in the TYR gene.  Other types of autosomal recessive albinism are OCA3 (203290 ), and OCA4 (606574). 

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available for the hypopigmentation.  Low vision aids can be helpful. Significant refractive errors should, of course, be corrected and dark lenses may be helpful during outdoor activities. The skin should be protected from excessive sun exposure. 

References
Article Title: 

Vision in albinism

Summers CG. Vision in albinism. Trans Am Ophthalmol Soc. 1996;94:1095-155.

PubMed ID: 
8981720

Oculocutaneous albinism

Gronskov K, Ek J, Brondum-Nielsen K. Oculocutaneous albinism. Orphanet J Rare Dis. 2007 Nov 2;2:43. Review.

PubMed ID: 
17980020
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