Albinism in humans

Albinism is a congenital genetic condition characterised by the partial or complete absence of melanin, the pigment responsible for colouring the skin, hair and eyes in humans and many other organisms. Present in all vertebrate groups, albinism manifests through a spectrum of pigmentation deficiencies, often accompanied by visual disturbances. Although individuals with albinism typically experience normal growth and development, the lack of protective melanin increases susceptibility to sun-induced skin damage and other health complications in certain environments.

Biological Basis and Types

Melanin synthesis depends on the activity of tyrosinase, a copper-containing enzyme that converts the amino acid tyrosine into pigment. Albinism results when mutations affect tyrosinase itself or other proteins involved in melanin production or the transport of pigment granules within cells. In humans this condition is generally hereditary, arising from recessive alleles inherited from both parents, though rarer non-recessive patterns also exist.
Two principal forms are recognised:

• Oculocutaneous albinism (OCA): affects skin, hair and eyes. Multiple genotypes (e.g., OCA1, OCA2, OCA3) correspond to different gene mutations producing a range of pigmentation from complete absence to reduced or reddish–brown variants.
• Ocular albinism (OA): affects the eyes alone and is most commonly inherited through X-linked transmission, resulting in a higher prevalence among males.

In zoology, the term albino is reserved for organisms lacking melanin entirely, whereas individuals with reduced pigmentation are described as leucistic or albinoid.

Clinical Features

The most visible indicators of albinism involve pigmentation:

• Skin and hair: may appear white, very pale, or lighter than familial norms. Some forms allow limited pigment development.
• Eyes: irides vary from blue to brown but appear translucent when illuminated laterally due to low pigment. Red-eye in photographs is common because the retina is visible through the iris.

Pigment deficiency in the eyes significantly affects vision. Melanin is essential for normal development of the optic system, and its absence disrupts the routing of optic nerve fibres. Key visual symptoms include:

• Reduced visual acuity from macular hypoplasia and retinal straylight
• Nystagmus, an involuntary oscillation of the eyes
• Strabismus and underdevelopment of the optic nerve
• Photophobia, often alleviated with sunglasses or broad-brimmed hats

Despite these visual impairments, albinism alone does not reduce life expectancy. The main health risk arises from ultraviolet radiation; individuals are prone to severe sunburn and are at elevated risk of developing skin cancers without proper protection.
Rare syndromic forms, such as Chediak–Higashi syndrome, involve defects in pigment granule transport that also impair immune cell function, leading to heightened vulnerability to infections.

Genetics

OCA is most commonly inherited in an autosomal recessive pattern: unaffected parents may both carry a mutation and have children with albinism. Genes implicated include TYR (OCA1), OCA2, TYRP1 (OCA3) and several others. Each mutation interferes with melanin production in different ways. For example, OCA3 is associated with TYRP1 gene variants that change the balance of brown and black melanin synthesis.
Ocular albinism, by contrast, exhibits an X-linked pattern. Males with a single mutated X chromosome are affected, whereas females with one mutated allele are typically carriers.
Albinism occurs equally in males and females except for the X-linked ocular form. Two variants are broadly recognised:

• Hypomelanosis: reduced melanin
• Amelanosis: complete absence of melanin

Evolutionary Perspectives

Human albinism provides insight into the evolution of skin pigmentation. Early Homo populations likely exhibited light skin beneath their hair, similar to modern chimpanzees. As body hair was lost over evolutionary time, dark melanin-rich skin offered protection against intense equatorial ultraviolet radiation. Possession of the eumelanin-producing MC1R allele conferred a survival advantage, influencing reproductive fitness in early African populations.
The evolutionary pressures acting on albinism differ geographically. In equatorial regions, the absence of melanin leads to a higher incidence of lethal or debilitating UV-related conditions, contributing to reduced survival rates. Studies in Nigeria indicate a markedly young age distribution among people with albinism, suggesting environmental selection.
Conversely, in some non-equatorial populations cultural practices may have offset environmental disadvantages. Among the Hopi of North America, the elevated prevalence of albinism has been linked to a high social status accorded to albino males, who were ritually esteemed and shielded from sun exposure, allowing them greater reproductive success.

Diagnosis

Diagnosis is usually clinical, based on characteristic pigmentation and ocular features. Genetic testing can confirm specific OCA or OA subtypes and can identify syndromic forms where albinism co-occurs with other medical conditions. While genetic confirmation offers no direct medical treatment for OCA itself, it is valuable for:

• distinguishing between albinism subtypes
• identifying associated systemic disorders
• informing family planning and genetic counselling

Management

There is no cure for albinism, but supportive measures greatly improve quality of life:

• Sun protection: high-SPF sunscreen, protective clothing and avoidance of excessive UV exposure
• Visual support: corrective lenses, low-vision aids and orientation training; early intervention is especially important in children
• Eye care: regular ophthalmologic monitoring, treatment of strabismus and management of nystagmus symptoms