OMIM ID:
Albinism, Oculocutaneous, Type III
Alternate Names
Defective Genes
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
Inheritance
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
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.