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Clinical Aspects of Albinism
Doctor Loredana Boccone
Albinism is a heterogeneous group of hereditary anomalies of the melanin synthesis characterized by a congenital lowering or total absence of the melanic pigment in the skin, hair and eyes (Ocular-cutaneous Albinism, OCA) or almost exclusively in the eyes (Ocular Albinism, OA).
A lot of confusion has been generated with the attempt of classification on the basis of the phenotypical characteristics.
Starting from the 90's, molecular analysis allowed a more accurate classification based on specific genes involved. This classification has improved and keeps improving year after year.
Nowadays only the classification according to the concerned genetic locus is the most correct.
Despite the wide variability of the clinical presentations the basic concept to define albinism remains unchanged, that is: the ocular disorders that are related to the reduction of melanin during the embryonic development and after birth, and are pathognomonic for the diagnosis of albinism. Depigmentation of skin and hair are associated to the ocular-cutaneous forms of albinism.
The ocular clinic signs are usually represented by:
» Congenital Nystagmus
» Photophobia
» Alternating Strabismus
» Visual Deficit
Besides the ocular signs, which are common to every form of albinism, congenital hypopigmentation which affects skin, hair and eyes is called ocular-cutaneous albinism or OCA, when it mainly affects the eyes it is called ocular albinism or OA.
OCA can be classified into two groups: non-syndromic OCA and syndromic OCA.
Non-Syndromic OCA occurs when there is a reduction in the melanogenesis casued by a defect of the proteins involved in this process, whilst Syndromic Albinism is due to the alteration of the proteins involved in the synthesis and traffic of the organelles associated to the lysosomes, who not only include melanosomes, but also the thick bodies of platelet and lysosomes.
Non-Syndromic OCA includes four genetically different forms: OCA1, OCA2, OCA3 and OCA4 which can present a high phenotypic variation with an overlap of the clinic scene and can be differentiated on the basis of the molecular study.
Syndromic OCA includes the S.Hermanski-Pudlak, the S.Chediak-Higashi and the S.Griscelli.
All forms of Ocular-cutaneous Albinism are transmitted with an autosomal recessive mode and the risk of recurrence is 25%.
Ocular Albinism is characterized by alterations of the ocular system with no alterations of the colour of the skin and hair, it is inherited with an X-linked mode and expresses itself only with homozygous males and the risk of recurrence is 50% in sons.
Being a genetic disease, treatments for albinism are limited.
Patients affected by albinism must implement a series of measures to protect the skin from ultraviolet radiation and undergo annual dermatologic visits to prevent complications related to the possible development of skin cancer.
Ophthalmologic care concerns the correction of myopia and astigmatism to achieve the maximum vision acuity and eye exams should be performed annually.
Prenatal diagnosis can be peformed for all forms of albinism when the mutation responsible is known.
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