Albinisme

01Pathophysiology

Albinism is a group of autosomal recessive (in most forms) genetic disorders resulting from defective melanin biosynthesis. The critical concept to understand is that melanocytes are present in normal numbers, but they cannot produce melanin properly. This distinguishes albinism from vitiligo, where melanocytes are destroyed or absent.

The melanin synthesis pathway begins with the amino acid tyrosine. The enzyme tyrosinase catalyzes the rate-limiting step: the hydroxylation of tyrosine to DOPA (dihydroxyphenylalanine) and then the oxidation of DOPA to dopaquinone. From dopaquinone, the pathway branches into eumelanin (brown-black pigment) and pheomelanin (red-yellow pigment). In OCA1, the TYR gene encoding tyrosinase is mutated, leading to complete (OCA1A) or partial (OCA1B) loss of enzyme activity. When tyrosinase is completely absent, no melanin of any type can be formed, producing the most severe phenotype with snow-white hair, milky skin, and blue-gray irides.

In OCA2, the second most common form, the defect lies in the OCA2 (P) gene, which encodes a melanosomal transmembrane protein involved in pH regulation of the melanosome. Melanosomes require an acidic environment for optimal tyrosinase function. When the P protein is dysfunctional, melanosomal pH is disrupted, and melanin production is reduced but not entirely abolished. This is why OCA2 patients often retain some pigment, and pigmentation may increase slightly with age.

The ocular findings in albinism are explained by the role of melanin in eye development. During embryogenesis, retinal pigment epithelium (RPE) melanin is required for proper development of the fovea and for correct routing of optic nerve fibers at the optic chiasm. Without adequate melanin, foveal hypoplasia occurs (the foveal pit fails to develop normally), which accounts for the permanently reduced visual acuity. Additionally, there is misrouting of the optic nerve fibers: an excessive proportion of temporal retinal fibers cross at the chiasm to the contralateral hemisphere, resulting in abnormal binocular vision and contributing to nystagmus and strabismus. This misrouting can be detected by visual evoked potentials (VEPs), which show asymmetric responses.

The lack of melanin in the iris means the iris cannot block light effectively, producing iris transillumination on slit-lamp examination. The iris appears translucent or reddish because light passes through the poorly pigmented stroma and reflects off the retinal vasculature.

From a dermatologic standpoint, melanin normally serves as a natural photoprotectant by absorbing ultraviolet (UV) radiation and scavenging free radicals. Without this shield, patients with albinism suffer cumulative UV-induced DNA damage. This explains the dramatically elevated risk of squamous cell carcinoma and other UV-related skin malignancies, particularly in tropical regions with high sun exposure.

02Classification and Clinical Manifestation

Oculocutaneous Albinism (OCA) Subtypes

Syndromic Forms of Albinism

Ocular Albinism

03Diagnostic Workup

The diagnosis of albinism is primarily clinical. When a newborn or infant presents with generalized hypopigmentation of skin, hair, and eyes, accompanied by nystagmus and photophobia, the diagnosis is usually apparent. The ophthalmologic examination is a cornerstone of the initial workup: slit-lamp evaluation reveals iris transillumination defects, and fundoscopy demonstrates foveal hypoplasia (absence of the normal foveal light reflex and underdeveloped foveal pit). These ocular findings are present in essentially all forms of albinism, including OCA and ocular albinism.

Genetic testing has become the confirmatory standard. Targeted gene panel testing or whole exome sequencing identifies the causative mutation, which is important for three reasons: (1) it confirms the subtype and provides prognostic information, (2) it enables accurate genetic counseling for the family regarding recurrence risk, and (3) it distinguishes syndromic from non-syndromic forms. For example, identifying an HPS gene mutation alerts clinicians to screen for bleeding complications and pulmonary fibrosis.

If a syndromic form is suspected clinically, additional targeted workup is necessary. A patient with albinism and unexplained bruising or prolonged bleeding time should raise suspicion for Hermansky-Pudlak syndrome; platelet aggregation studies will show absent secondary aggregation wave, and electron microscopy of platelets confirms absent dense granules. A patient with albinism and recurrent severe bacterial infections warrants a peripheral smear looking for the pathognomonic giant cytoplasmic granules of Chediak-Higashi syndrome.

The hair bulb incubation test is now largely of historical interest but is still occasionally referenced: a plucked hair bulb is incubated with L-tyrosine or L-DOPA. In OCA1A, no pigment forms (tyrosinase-negative). In OCA1B and OCA2, some pigment develops (tyrosinase-positive). This test has been largely replaced by molecular diagnostics.

04Management and Treatment

There is no cure for albinism, and no treatment restores normal melanin production.

Management is entirely supportive and preventive.

Photoprotection is the single most important intervention for long-term morbidity and mortality. In tropical and equatorial regions, where UV exposure is intense and sustained, patients with albinism face a dramatically elevated lifetime risk of actinic keratoses, squamous cell carcinoma, and basal cell carcinoma. Many affected individuals in sub-Saharan Africa develop skin cancers before age 30. Broad-spectrum sunscreen with a minimum SPF of 30 should be applied daily to all exposed areas, with reapplication every 2 hours during outdoor activities. Physical barriers (long sleeves, hats, UV-protective sunglasses) are equally or more important than chemical sunscreens and should be used consistently.

Ophthalmologic management focuses on optimizing visual function, since foveal hypoplasia and optic misrouting cause permanent visual impairment that cannot be corrected surgically. Refractive errors (commonly high astigmatism and hyperopia) should be corrected with appropriate lenses. Low-vision aids, large-print materials, preferential classroom seating, and educational accommodations are often necessary. Nystagmus may diminish slightly with age but does not resolve. Strabismus surgery may be considered for cosmetic or functional benefit.

For Hermansky-Pudlak syndrome, the bleeding diathesis requires avoidance of aspirin and NSAIDs (which further impair platelet function). DDAVP (desmopressin, 0.3 mcg/kg IV) can be used preoperatively or during bleeding episodes to improve hemostasis. Platelet transfusions are reserved for severe or life-threatening hemorrhage. Patients with HPS subtypes 1 and 4 should undergo baseline and serial pulmonary function testing, as progressive pulmonary fibrosis is a leading cause of death in these subtypes. Pirfenidone has been studied as an antifibrotic agent in this context.

For Chediak-Higashi syndrome, the only curative treatment for the immunologic defect is allogeneic hematopoietic stem cell transplantation (HSCT). This should ideally be performed early, before the onset of the "accelerated phase" (hemophagocytic lymphohistiocytosis), which carries high mortality. HSCT corrects the immune deficiency and hematologic abnormalities but does not reverse the oculocutaneous albinism or the progressive neurologic decline.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on albinism questions is by failing to recognize the syndromic forms. A straightforward vignette of a pale child with nystagmus is easy. The trap comes when the test-writer adds a second feature: "easy bruising" (think Hermansky-Pudlak) or "recurrent skin abscesses" (think Chediak-Higashi). Students who do not link these associated findings to the underlying albinism will miss the diagnosis entirely or select an incomplete answer.

Another frequent error is confusing albinism with vitiligo. Both involve hypopigmentation, but the distinction is fundamental: albinism is congenital and generalized with melanocytes present; vitiligo is acquired and patchy with melanocytes absent. If the vignette describes a child who was "normal at birth and developed white patches over time," that is vitiligo, not albinism.

Students also sometimes overlook that ocular findings are universal in albinism and are often the clue that distinguishes it from other causes of congenital hypopigmentation. If a fair-skinned child has nystagmus, foveal hypoplasia, and iris transillumination, the diagnosis is albinism regardless of the degree of cutaneous pigment reduction.

Finally, remember that the inheritance of most OCA forms is autosomal recessive, meaning both parents are typically unaffected carriers. The exception tested most often is ocular albinism type 1 (Nettleship-Falls), which is X-linked recessive, so it predominantly affects males while carrier females may show subtle mosaic fundus findings. When a vignette describes an affected boy with a maternal uncle who has similar ocular problems but normal skin, think X-linked ocular albinism.

The core competency being tested is the ability to (1) recognize the clinical phenotype of albinism, (2) correctly identify the associated syndromic conditions based on additional clinical clues, and (3) understand the genetic basis and inheritance pattern well enough to provide accurate counseling and predict recurrence risk.