Hypopigmentation, Strabismus and Ocular Albinism
When AS is caused by the large deletion, skin and eye hypopigmentation usually result. This occurs because there is a pigment gene (the P gene, also termed OCA2), located close to the AS gene, that is also missing [1]. This pigment gene produces a protein that is believed to be crucial in melanin synthesis. Melanin is the main pigment molecule in our skin. In some children with AS, this hypopigmentation can be so severe that a form of albinism is suspected[2]. When AS is caused by the other genetic mechanisms, this gene is not missing and thus normal skin and eye pigmentation is seen. Children with AS who have hypopigmentation are sun sensitive, so use of a protective sun screen is important. Not all AS children with deletions of the P gene are obviously hypopigmented, but may only have relatively lighter skin color than either parent.
Surveys of individuals with AS demonstrate an increased incidence of strabismus. This problem appears to be more common in children with hypopigmentation (as above), since pigment in the retina is crucial to normal development of the optic nerve pathways. Management of strabismus in AS is similar to that in other children: evaluation by an ophthalmologist, correction of any visual deficit, and where appropriate, patching and surgical adjustment of the extraocular muscles. The hypermotoric activities of some AS children will make wearing of patches or glasses difficult but many are able to accomplish this.
1. Lee ST, Nicholls RD, Bundey S, et al. Mutations of the P gene in oculocutaneous albinism, ocular albinism, and Prader-Willi syndrome plus albinism. N Engl J Med, 1994. 330(8): p. 529-34.
2. King RA, Wiesner GL, Townsend D, et al. Hypopigmentation in Angelman syndrome. Am J Med Genet, 1993. 46(1): p. 40-4.