40.1 Features

Albinism is a rare genetically heterogeneous inherited disorder of impaired melanin biosynthesis that is characterized by specific changes in the eye and visual pathway with or without reduced pigmentation of the skin and hair. There are two main forms: oculocutaneous albinism (OCA) and ocular albinism (OA). Patients with OA have only the ocular and optic changes that result from reduced melanin pigment during development, while those with OCA also have depigmentation of the skin, hair, and eyelashes.

OA can arise from either autosomal recessive or X-linked recessive mutations, while all subtypes of OCA have an autosomal recessive inheritance pattern. Autosomal recessive ocular albinism (AROA) results from mutations in TYR and TYRP1, while X-linked mutations in the GPR143 gene at Xp22.2 lead to OA1, the Nettleship-Falls variant of OA (MIM #300500). Different genetic mutations can lead to variable phenotypic expression. Patients with mutations in the tyrosinase (TYR) gene on chromosome 11q14-q21 develop OCA type 1 (OCA1), which is characterized by white hair and fair skin. However, those with OCA1B (MIM #606952) can develop some melanin pigment in their eyes, hair, and skin, while those with OCA1A (MIM #2031100) do not develop any melanin pigment. Patients with OCA2 have mutations in the OCA2 gene (chromosome 15q12-q13, MIM #203200). Less commonly, patients can develop OCA3 from mutations on the tyrosinase-related protein 1 (TYRP1) gene. Patients with OCA3 tend to develop a milder phenotype. Those with SLC45A2 mutations develop OCA4 (MIM #606574), which is characterized by a wide array of phenotypic expression. A new gene OCA5 (MIM #615312) has been identified on chromosome 4q24, and OCA6 (MIM#203100) is due to mutations on SLC24A5 on chromosome 1q21.1. In rare circumstances, OCA is associated with potentially fatal systemic syndromes such as Chédiak-Higashi (CHS) and Hermansky-Pudlak (HPS).

40.1.1 Common Symptoms

Extreme photophobia and glare symptoms result from light easily entering and scattering inside the eyes. Systemic syndromes can have life-threatening and debilitating comorbidities (e.g., frequent pyogenic sinopulmonary or skin infections and peripheral neuropathy in CHS; blood clotting disorders, and ceroid accumulations in the lungs and kidneys in HPS).

40.1.2 Exam Findings

A pendular sensory nystagmus develops due to poor development of the optic system. During infancy, the patient’s eye movements may have a low frequency and large amplitude that later evolve into the more distinct fast and slow phases in adulthood. Because they have a positive angle kappa, they often have the external appearance of pseudoexotropia. Concomitant strabismus and loss of stereopsis are possible and may lead to a head tilt. Patients with albinism who have less pigment have worse visual acuity, though visual acuity tends to be better at near than distance because convergence helps dampen the nystagmus at near.

On slit lamp exam, albinos demonstrate speckled or diffuse transillumination defects and variable depigmentation of the iris (▶ Fig. 40.1). Patients with more severe OCA1A can have light blue to pink irides, while those with less severe forms, like OCA1B, may have green or brown irides. Patients with OCA2, -3, and -4 may have better visual acuity than patients with OCA1 and can demonstrate increases in pigmentation over time in the iris, skin, choroid, and retinal pigment epithelium (RPE). Hypopigmentation of the RPE may reveal visible choroidal macular vessels on dilated fundus exam, and foveal hypoplasia leads to absence of the foveal pit and the foveal light reflex (▶ Fig. 40.2). Patients with OA and AROA demonstrate similar ocular findings to OCA but have normal pigmentation of the skin and hair.

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