Albinism is characterized by hypopigmentation of the skin, hair, and eyes, or of eyes only, in the affected individuals. There are 2 albinism subtypes are nonsyndromic albinism, with symptoms restricted to impaired melanin biosynthesis (hypopigmentation of skin and hair, and ocular changes such as reduced iris pigment, nystagmus, impaired visual acuity, and foveal hypoplasia), and syndromic albinism, such as Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, and Griscelli syndrome, with various nonpigmentary symptoms, including bleeding diathesis, lung fibrosis, and immunodeficiency. Other congenital disorders involving pigmentation include a wide range of disorders such as piebaldism, Waardenburg syndrome, and reticular pigmentary disorders including dyschromatosis symmetrica hereditaria, dyschromatosis universalis hereditaria, reticulate acropigmentation of Kitamura, and Dowling-Degos disease. This chapter discusses all of the disorders listed above.
Oculocutaneous albinism is a group of rare genetic disorders with autosomal recessive inheritance, characterized by hypopigmentation of skin, hair, and eyes.
Seven subtypes and 6 responsible genes (all except for type 5) have been described.
In addition to hypopigmentation, extrapigmentary symptoms in GS1 and GS2 are neurologic abnormalities and hematologic immunodeficiency/abnormalities, respectively. On the other hand, GS3 is restricted to hypopigmentation.
In some types, hypopigmentation of the skin may gradually improve as the individual grows; the exception is type 1A, where melanin biosynthesis is completely absent.
Visual disturbances consist of nystagmus, impaired visual acuity, and stereoscopic vision.
Protection of skin from the sun is required to prevent sunburn and secondary skin change, including solar degeneration and skin cancer.
Early referral to an ophthalmologist is important to introduce proper ophthalmologic intervention.
Oculocutaneous albinism (OCA) is a rare genetic condition with autosomal recessive inheritance, and it is characterized by hypopigmentation of skin, hair, and eyes. Currently 7 types of OCA have been identified (Table 75-1), and all of the genes responsible, with the exception of OCA5 (for which the responsible gene has not yet been identified), are associated with melanin biosynthesis or migration of melanocytes/melanocyte precursor cells. The overall prevalence of OCA is estimated at approximately 1:10,000 to 20,000 people; however, the incidence of each type varies depending on geographic region and ethnicity. Some types of albinism are seen more frequently in certain regions as a result of the founder effect.1
TABLE 75-1Ocular Albinism and Oculocutaneous Albinism (Nonsyndromic Albinism) ||Download (.pdf) TABLE 75-1 Ocular Albinism and Oculocutaneous Albinism (Nonsyndromic Albinism)
|DISEASE NAME ||INHERITANCE ||GENES ||CHROMOSOMAL LOCATION ||OMIM # |
|OCA1 ||AR ||TYR ||11q14.3 ||203100 |
|OCA2 ||AR ||OCA2 ||15q12-q13.1 ||203200 |
|OCA3 ||AR ||TYRP-1 ||9p23 ||203290 |
|OCA4 ||AR ||SLC45A2 ||5p13.2 ||696574 |
|OCA5 ||AR ||Unknown ||4q24 ||615312 |
|OCA6 ||AR ||SLC24A5 ||15q21.1 ||609802 |
|OCA7 ||AR ||C10orf11 ||10q22.2-q22.3 ||615179 |
|OA1 ||X-linked ||GPR143 ||Xp22.3 ||300500 |
OCULOCUTANEOUS ALBINISM TYPE 1
OCA1 appears to be the most ...