This is a genetically determined, heterogeneous group of conditions characterized by failure of normal synthesis of melanin and reduced pigmentation in the skin, hair and eyes. Albinism has historically been classified according to the site and severity of melanin deficiency:
- Oculocutaneous albinism – hair, skinand eyes are affected. Tyrosinasenegative oculocutaneous albinism is an autosomal recessive condition with complete absence of melanin. Tyrosinase-positive patients synthesize variable amounts of melanin. Their complexion varies from very fair to normal; eye involvement is also variable
- Ocular albinism – decreased ocular pigment only. The skin and hair appear essentially normal, although all albinos have some degree of hypopigmentation. Inheritance is usually X-linked recessive.
Pathologically, there is a deficiency in the enzyme tyrosine kinase, which is involved in the conversion of tyrosine to melanin. Mutations have been found on chromosomes 9, 11 and 15. The optic chiasm is unusual in oculocutaneous albinism, in that the majority of fibres in each eye cross into the opposite
Decreased vision and photophobia.
Tyrosinase-negative patients have profoundly pale skin and white hair. Visual acuity is usually less than 6/60, with a combination of myopic and astigmatic errors. A pendular, horizontal nystagmus appears at 2-3 months of age. There is a pink reflex through an undilated pupil, and
the iris transilluminates. Foveal hypoplasia is invariably present, and is manifested by the absence of the normal bright foveal reflex and foveal pit. Other findings include prominent choroidal vessels and optic disc hypoplasia. Female carriers of ocular albinism have partial iris transillumination and scattered areas of reduced pigmentation in the peripheral retina.
Albinism is rare (1 in 20,000).
Tyrosinase-negative patients usually have profound visual impairment from an early age. Patients with oculocutaneous albinism have an increased risk of skin cancer. Several rare syndromes are associated with albinism and may present with symptoms such as recurrent bruising, bleeding or infection. These patients ma be at risk of developing a lymphomatous condition. Referral to a hematologist for further testing is appropriate.
Advice and vision aids Currently, there is no effective treatment for albinism. Corrective lenses provide limited improvement in visual acuity, and tinted lenses alleviate photophobia. Barrier protection against
ultraviolet radiation is recommended. Lowvision aids are important at home and in the educational and occupational environments (e.g. small telescopes for viewing the blackboard). The patient should be encouraged to report the appearance of suspicious skin lesions.
Blood tests and referral Clotting studies are
performed before surgery. Consultation and regular review with a dermatologist is recommended.
Genetics Consideration of the disease pattern and thorough documentation of the family history will help determine the
inheritance pattern involved. The implications can be explained; for example, on average, one-quarter of the children of carrier parents of autosomal recessive oculocutaneous albinism will be affected. When inheritance is X-linked recessive, an affected maie will pass on the abnormal gene to all of his daughters (they will, with rare exceptions, be carriers)
and to none of his sons (as the Y chromosome does not carry the mutation). Referral to a geneticist is often appropriate.
Surgery Extraocular muscle surgery may be beneficial in selected patients with severe strabismus or abnormal head position due to nystagmus.
Slit-lamp microscopy demonstrating iris transillumination.
Pale fundus with prominent choroidal vessels and macular dysplasia with loss of macular reflex.