Oculocutaneous albinism type I

Alternate names

OCA1; Oculocutaneous albinism type 1A; OCA1A; Oculocutaneous albinism, tyrosinase negative; ATN; Albinism 1

Definition

Oculocutaneous albinism type 1 is a condition that affects the coloring of the skin, hair, and eyes.

Types

OCA1 is divided into two categories:

• OCA1A, associated with no melanin synthesis in any tissue, and
• OCA1B, associated with minimal amounts of melanin synthesis in the hair, skin, and eyes.

The ocular features of OCA1A and OCA1B are identical except for the amount of iris pigment.

Cause

OCA1A is caused by null variants in TYRgene that produce a completely inactive or an incomplete tyrosinase enzyme polypeptide. The total lack of tyrosinase enzyme function blocks the first step of the melanin biosynthetic pathway and, thus, no melanin forms in any melanocyte. OCA1B is caused by pathogenic variants in TYR that produce a partially active or hypomorphic tyrosinase enzyme.

Inheritance

Autosomal recessive inheritance, a 25% chance

OCA1 is inherited in an autosomal recessive manner, which means both copies of a gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they do not show signs and symptoms of the condition.

Signs and symptoms

Oculocutaneous albinism type 1 (OCA1) is characterized by hypopigmentation of the skin and hair and the distinctive ocular changes found in all types of albinism, including: nystagmus; reduced iris pigment with iris translucency; reduced retinal pigment with visualization of the choroidal blood vessels on ophthalmoscopic examination; foveal hypoplasia with substantial reduction in visual acuity, usually in the range of 20/100 to 20/400; and misrouting of the optic nerve fiber radiations at the chiasm, resulting in strabismus, reduced stereoscopic vision, and altered visually evoked potentials (VEP). Individuals with OCA1A have white hair, white skin that does not tan, and fully translucent irides, none of which darken with age. At birth, individuals with OCA1B have white or very light yellow hair that darkens minimally with age, white skin that over time develops some minimal generalized pigment and may tan slightly with judicious sun exposure, and blue irides that darken to green/hazel or light brown/tan with age, although transillumination defects persist. Visual acuity may be 20/60 or better in some eyes.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Abnormal morphology of the choroidal vasculature
• Abnormality of visual evoked potentials
• Blue irides(Blue eyes)
• Cutaneous photosensitivity(Photosensitive skin)
• Depigmented fundus
• Generalized hypopigmentation(Fair skin)
• Generalized hypopigmentation of hair
• Hypoplasia of the fovea
• Iris hypopigmentation(Light eye color)
• Iris transillumination defect
• Nystagmus(Involuntary, rapid, rhythmic eye movements)
• Optic nerve misrouting
• Photophobia(Extreme sensitivity of the eyes to light)

30%-79% of people have these symptoms

• Amblyopia(Lazy eye)
• Strabismus(Cross-eyed)
• White eyebrow(Pale eyebrow)
• White eyelashes(Blonde eyelashes)

5%-29% of people have these symptoms

• Thickened skin(Thick skin)

1%-4% of people have these symptoms

• Actinic keratosis

Diagnosis

• The diagnosis of OCA1 is established by clinical findings of profound hypopigmentation of the skin and hair and characteristic ocular findings.
• Molecular genetic testing of TYR (encoding tyrosinase) is used infrequently in diagnosis, except to distinguish between types 1A and 1B, as the phenotypes may be nearly identical in the first year of life.

Treatment

• Correction of refractive errors with spectacles or (when age-appropriate) contact lenses may improve visual acuity; strabismus surgery can be considered for either functional (improved peripheral fusion) or cosmetic reasons.
• Hats with brims and dark glasses or transition lenses often reduce discomfort in bright light (photodysphoria).
• Protection from sun exposure with appropriate skin-covering clothing and sunscreens prevents burning, consequent skin damage, and the enhanced risk of skin cancer.
• Skin cancer, including a slightly enhanced risk for cutaneous melanoma, is treated as for the general population.[1].

NIH genetic and rare disease info

• NIH info on Oculocutaneous albinism type I

Oculocutaneous albinism type I is a rare disease.

Oculocutaneous albinism type I Resources
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