Albinism overview
|
Albinism Microchapters |
|
Diagnosis |
|---|
|
Treatment |
|
Case Studies |
|
Albinism overview On the Web |
|
American Roentgen Ray Society Images of Albinism overview |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Shadan Mehraban, M.D.[2]
Overview
Albinism is an inherited disease that is caused by a genetic mutation. This mutation impairs melanin synthesis; therefore, the number of melanocytes is preserved. The different types of albinism include, Oculocutaneous albinism(OCA), Hermansky-Pudlak syndrome (HPS),Chediak-Higashi syndrome (CHS), and Ocular albinism (OA). Patients may present cutaneous and ocular findings. Cutaneous features include hypopigmented/ white hair, skin, and eyelashes. Ocular features include photophobia, decreased visual acuity, pink eyes, and hypopigmentation of iris, refractive errors, strabismus, nystagmus, foveal hypoplasia, and iris transillumination. The management of cutaneous and ocular manifestations of albinism include avoidance of prolonged sun exposure, periodic dermatologist evaluation for skin cancer, corrective lenses for refractive errors, tinted lenses/glasses for photophobia, bifocal or low-vision aids in older children, eye-patching in infants for reduction of strabismus, contact lenses or eye surgery in presence of nystagmus. Additionally, nitisinone can be used to improve pigmentation in OCA1.
Historical Perspective
Albinism was first discovered in 1908 by a British physician named Sir Archibald Edward Garrod. At first, it was believed that albinism is caused by a lack of melanocytes. In late 1950, it was proved that albinism is caused by tyrosine kinase inactivity.
Classification
Albinism is classified based on genetic mutation. The different types of albinism include Oculocutaneous albinism(OCA), Hermansky-Pudlak syndrome (HPS),Chediak-Higashi syndrome (CHS), and Ocular albinism (OA).
Pathophysiology
Melanocytes are derived from neural crest ectoderm and are found in hair follicles, skin, eyes, and inner ear. Melanocytes produce melanin which protects skin from ultraviolet. Tyrosinase converts tyrosine to DOPA, dopaquinone, and then melanin. Mutation in Tyrosinase enzyme is responsible for causing albinism. Additionally, melanin is responsible for development of the fovea, optic nerves, optic tracts, and visual cortex.Decussation of some optic nerve fibers at optic chiasm are essential for binocular vision. However, in albinism, most of nerve fibers decussate at optic chiasm and cause monocluar vision presented as strabismus. In ocular albinism, macular pigment is absent and fovea hypoplasia leads to decreased visual acuity.
Causes
Albinism is caused by genetic mutations that impair melanin synthesis. The number of melanocytes is preserved.
Differentiating Albinism from other Diseases
Oculocutaneous albinism and ocular albinism must be differentiated from the following rare disease: Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, Griscelli syndrome, Waardenburg syndrome type II, Vici syndrome, Tietz albinism-deafness syndrome, Angelman syndrome, Prader-Willi syndrome, Cross-McKusick-Breen syndrome, Achromatopsia, Aland Island eye disease (Forsius-Eriksson syndrome), Aniridia, and Congenital nystagmus.
Epidemiology and Demographics
The prevalence of albinism is estimated to be 1:17,000 to 1: 20,000 in the general population.The Prevalence of different types of albinism varies and the most prevalent form is Oculocutaneous albinism 2 (OCA2).
Risk Factors
Albinism is inherited due to genetic mutations. Individuals with positive familial history are at risk of having albinism.
Screening
There is no screening test for albinism.Individuals with familial history of albinism can undergo genetic sequence analysis.
Natural History, Complications and Prognosis
The complications of albinism include skin cancer, sunburn, decreased visual acuity, poor self-image and self-isolation lead to depression. Patients with albinism has a normal life expectancy and do not have developmental delay or mental retardation.
Diagnosis
History and Symptoms
Patients may present both cutaneous and ocular findings. Cutaneous features include hypopigmented/ white hair, skin, and eyelashes. Ocular features include photophobia, decreased visual acuity, pink eyes, and hypopigmentation of iris.
Physical Examination
Ocular physical examination findings include refractive errors, strabismus, nystagmus, foveal hypoplasia, iris transillumination, decreased iris pigmentation. Cutaneous finding varies from white to hypopigmented or light brown skin, hair, eyebrow, and eyelashes.
Laboratory Findings
The laboratory tests for diagnosis of albinism include hair bulb assay for determination of tyrosinase activity, Genetic sequence testing which is the most definite test, bleeding tests in suspected patients with Hermansky-Pudlak syndrome, and evaluation of polymorphonuclear leukocyte function in suspected patients with Chediak-Higashi syndrome.
Electrocardiogram
There are no electrocardiogram findings associated with albinism.
X Ray
There are no x-ray findings associated with albinism.
CT
There are no CT findings associated with albinism.
MRI
There are no MRI findings associated with albinism.
Echocardiography or ultrasound
There are no echocardiography or ultrasound findings associated with albinism.
Other Imaging Findings
Macular optical coherence tomography can be used in young patients with nystagmus and foveal abnormalities to determine the cause.
Other Diagnostic Studies
Ophthalmology examination and evaluation should be done to confirm the diagnosis. Visual-evoked potential testis used for recognition acuity in children and shows misrouting of optic nerves.
Treatment
Medical Therapy
The management of cutaneous and ocular manifestations of albinism include avoidance of prolonged sun exposure, periodic dermatologist evaluation for skin cancer, corrective lenses for refractive errors, tinted lenses/glasses for photophobia, bifocal or low-vision aids in older children, eye-patching in infants for reduction of strabismus, contact lenses or eye surgery in presence of nystagmus. Additionally, nitisinone can be used to improve pigmentation in OCA1.
Surgery
Eye muscles surgery can improve ocular alignment and vision in patients with severe ocular features. However, it may not be really helpful in strabismus improvement due to lack of necessary ocular connections.
Primary Prevention
Genetic consultation is recommended for couples diagnosed with albinism, familial history of albinism or parents of albino child who consider having future pregnancy.
Secondary Prevention
There is no secondary prevention for albinism.