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L'OCA1 (albinism tyrosinase-deficient) is determined by the mutation of the gene coding for tyrosinase, located on chromosome 11q14-21.
It is divided into two subtypes based on the amount and type of residual enzyme activity.
Mutant alleles associated with absent tyrosinase activity produce OCA1 (the classic tyrosinase-negative oculocutaneous albinism). Mutant alleles associated with some residual activity produce OCA1B, which presents a broad spectrum of manifestations.
Individuals with OCA, the classic tyrosinase-negative OCA, do not have any melanin synthesis in the skin, hair and eyes at any time during their lives and present a characteristic phenotype. They are born with white hair and white skin and blue eyes and do not undergo any change with age. Melanin never develops in these tissues. The phenotype is the same in all ethnic groups and all ages.
Over time, the hair can take on a more intense colour than the transparent white or pale yellow, but this is due to the denaturation of the hair protein linked to sun exposure or to the use of different shampoos. The irises are transparent; they appear pink during childhood and often turn to blue-grey over the time. There are no pigmented lesions of the skin, although there may be some amelanotic moles present.
OCULOCUTANEOUS ALBINISM 1A or OCA1A
OCA1A is the most severe form of albinism with an absence of pigment in the skin, hair and eyes since birth, this defect will remain the way for life.
OCULOCUTANEOUS ALBINISM 1B or OCA1B
At birth, most patients with OCA1B have little or no pigment at all and they are born with white hair. In the first or second decade of life, they develop a certain amount of melanin in the hair and skin. In some cases, melanin develops within the first year of life or even in the early months of life.
Hair colour changes from white to pale yellow to light blonde and it can turn dark blonde or brown during adolescence or adulthood. The irises can develop a visible brown reddish pigment, sometimes restricted to the inner iris.
Over time, the formation of pigmented freckles (melanotic) or pink (amelanotic) is possible in the exposed areas.
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