albinism

Albinism, Oculocutaneous, Type I

Clinical Characteristics
Ocular Features: 

Oculocutaneous albinism is a genetically and clinically heterogeneous condition.  It is congenital in origin and the combination of foveal hypoplasia and anomalous decussation of neuronal axons in the chiasm results in a permanent reduction of vision in the range of 20/50-20/200.  Most individuals have nystagmus, photophobia, and strabismus.  The iris usually is light blue and transmits light.  The retina lacks pigmentation as well.  The ocular features are similar in types IA and IB.  The iris may darken with age in type IB (606952 ). 

Systemic Features: 

There are generally no systemic abnormalities in these pigmentation disorders with the exception of sensorineural hearing loss in some, and, of course, complete absence of pigment in skin and hair.  Anomalous decussation of axons in the auditory system has been demonstrated in such cases and otic pigment is lacking in albinos.  The skin contains amelanic melanocytes but these cells contain granules similar to those of normal cells.   Some patients with residual tyrosinase activity (type 1B, 606952 ) develop some pigmentation of hair and skin, especially in cooler areas of the body such as the extremities. 

Genetics

This type of oculocutaneous albinism is caused by mutations in the TYR gene (11q14-q21) and inherited in an autosomal recessive pattern. 

Type IA (OCA1A) has no demonstrable tyrosinase activity while type IB (OCA1B, 606952) has a reduction in enzyme activity.  Yet other patients with mutations in TYR have a variant called 'yellow albinism' in which tyrosinase activity resembles that found in type IB.  To explain the difference in skin color, it has been suggested that an individual's background ethnicity may impact the pigmentation phenotype.

Other types also transmitted as autosomal recessive conditions are OCA2 (203200), OCA3 (203290), AND OCA4 (606574). 

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

There is no treatment for the basic disease but low vision aids may be helpful for some patients.  Dark glasses provide comfort for photophobic individuals.  The skin should be protected against sunburn. 

References
Article Title: 

A new hypothesis of OCA1B

Chiang PW, Drautz JM, Tsai AC, Spector E, Clericuzio CL. A new hypothesis of OCA1B. Am J Med Genet A. 2008 Nov 15;146A(22):2968-70.

PubMed ID: 
18925668

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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