Oculocutaneous albinism (OCA) is a group of genetic disorders characterized by a reduction or absence of melanin pigment in the skin, hair, and eyes. There are several types of OCA, and type 1 oculocutaneous albinism (OCA1) is one of them. The worldwide incidence of oculocutaneous albinism is 1 in 17.000 individuals, although it may vary between populations. The Cuna Indians (in Panama and Colombia) have the highest reported incidence, approximately 6 cases per 1.000 inhabitants.
Oculocutaneous albinism type 1 genetic testing is included in Diagnostiki Athinon Monogenic Diseases Genetic Testing along with approximately 100 other inherited diseases, including cystic fibrosis (71 mutations) and hereditary breast cancer (genes BRCA1 415 mutations & BRCA2 419 mutations).
The key features and aspects of type 1 oculocutaneous albinism are:
- Genetic Basis: OCA1 is typically caused by TYR gene mutations, which provide instructions for producing the enzyme tyrosinase. Tyrosinase is essential for the production of melanin from the amino acid tyrosine.
- Absence of Melanin: Individuals with OCA1 produce little to no melanin, resulting in very light skin, hair, and eye color. Melanin is responsible for skin, hair, and eyes pigmentation.
- Skin and Hair Characteristics: The skin in individuals with OCA1 is usually very fair or white and prone to sunburn. Hair color can range from white to light yellow or blond. Freckles and moles may be absent or very few.
- Eye Characteristics: The most noticeable feature of OCA1 is the lack of eye pigmentation. The irises may appear blue, and the red retina is often visible, giving the characteristic red-eye reflection in flash photography. Vision problems, such as nystagmus (involuntary eye movement) and reduced visual acuity, are common.
- Nystagmus and Strabismus: Individuals with OCA1 often have nystagmus (involuntary back-and-forth eye movement) and may also experience strabismus (crossed or misaligned eyes). These conditions can contribute to visual impairment.
- Visual Impairment: OCA1 is associated with visual impairment due to the absence or reduction of melanin in the retina. The severity of visual impairment varies among individuals, but many have some degree of decreased visual acuity.
- Subtypes: OCA1 can be further classified into two subtypes: OCA1A, where there is a complete absence of melanin production, and OCA1B, where minimal melanin production may occur later in life.
- Management: There is no cure for OCA1, and treatment is supportive. Sun protection, including sunscreen, sunglasses, and protective clothing, is essential to prevent sunburn and reduce the risk of skin cancer. Visual aids and interventions may be recommended to address visual impairment.
More Information
OCA1 is caused by homozygosis or compound heterozygosis of pathogenic variants in the TYR gene coding for the enzyme tyrosinase. Deficiency in this enzyme leads to insufficient melanin production.
The main difference with oculocutaneous albinism type 2 is that phenotypically, the type 2 form is less marked, and patients have some pigmentation. In addition, the gene involved is OCA2. However, it is sometimes difficult to differentiate between the two types of albinism based solely on the patient's physical characteristics because of the great phenotypic variability, even between people with precisely the same mutations.
Over 300 potentially pathogenic variants have been described in TYR. In addition, certain variants in the TYR and OCA2 genes could be related to the predisposition to develop amelanotic and hypomelanotic melanomas.
One of the mutations in the TYR gene that can cause type I ocular albinism is c.140G>A or G47D. This variant causes the substitution of an amino acid glycine for an aspartic, changes the structure of the protein, and thus impairs the tyrosinase function.
Some of the mutations in the TYR gene are more frequent in specific populations, such as c.1205G>A and c.140G>A, which are usually found in Caucasian patients. The c.1037-7T>A variant is predominant in the Ashkenazi Jewish population and patients of Italian origin.
Oculocutaneous albinism type 1 genetic testing analyzes the 30 most frequent pathogenic mutations of the TYR gene.
The technique used for genetic testing analyzes only the gene's specific mutations, which are the most important and frequent in the literature. However, it should be noted that there are likely other gene or chromosomal mutations in the gene to be tested that cannot be identified with this method. Different analysis techniques can be used for these cases, such as next-generation sequencing (NGS).
