Type 2 oculocutaneous albinism (OCA2) is another subtype of oculocutaneous albinism characterized by a genetic mutation that affects melanin production in the skin, hair, and eyes. Unlike OCA1, in OCA2, there is some residual activity of the tyrosinase responsible for melanin synthesis. OCA2 is sometimes referred to as "tyrosinase-positive albinism." The worldwide prevalence of OCA2 is estimated to be 1 in 38.000, except the African population, which has a prevalence of 1:3.900.
Type 2 oculocutaneous albinism 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 2 oculocutaneous albinism are:
- Genetic Basis: OCA2 is primarily caused by mutations in the OCA2 gene. The OCA2 gene provides instructions for producing a protein that is involved in the regulation of melanin production. Mutations in this gene can lead to reduced melanin synthesis.
- Variable Pigmentation: Individuals with OCA2 typically have more pigmentation than those with OCA1. Skin, hair, and eye color can vary widely and may include a range of shades from very light to brown. Various genetic factors influence the degree of pigmentation.
- Eye Characteristics: The eyes of individuals with OCA2 often have a blue or grayish hue, and they may appear lighter than those of individuals without albinism. Nystagmus (involuntary eye movement) and strabismus (misalignment of the eyes) are common, contributing to visual impairment.
- Hair and Skin Color: Hair color in OCA2 individuals can range from blond to brown. Skin color varies from very light to light brown. While individuals with OCA2 have more pigmentation than those with OCA1, they are still at an increased risk of sunburn and skin damage.
- Visual Impairment: OCA2 is associated with visual impairment, including reduced visual acuity and sensitivity to light. Vision problems may affect daily activities and may require visual aids for improvement.
- Management: Management of OCA2 involves addressing the consequences of reduced melanin production. Sun protection measures, including sunscreen, sunglasses, and protective clothing, are essential to minimize the risk of sun-induced skin damage. Visual aids and interventions may also be recommended to support individuals with visual impairment.
It's important to note that while OCA2 is associated with less severe pigment reduction compared to OCA1, it still presents challenges related to vision and skin health.
More Information
People with OCA2 have pathogenic variants in the OCA2 gene. This gene produces a protein involved in the transport of the enzyme tyrosinase to the melanosome, and alterations in the OCA2 gene affect melanin production.
OCA2 follows an autosomal recessive mode of inheritance and can manifest in compound heterozygosity, especially in non-African patients.
The difference with oculocutaneous albinism type 1 is that phenotypically the type 2 form is less severe, and patients accumulate small amounts of melanin with age.
Other syndromes can manifest with albinism and affect other genes, such as Hermansky Publak, Angelman, and Prader-Willi.
It has been observed that the presence of pathogenic OCA2 variants could be related to a greater predisposition to develop certain types of melanomas.
One of the best-known pathogenic variants described in the OCA2 gene is c.1327 C>T or V443I, which is the most frequent in Northern European patients. Several authors have observed that the presence of this variant in homozygosis or compound heterozygosis (one copy of this mutation together with another copy of another mutation in the OCA2 gene or in other genes related to type II albinism) produces oculocutaneous albinism.
Another pathogenic mutation in the OCA2 gene has been described as one that can lead to the development of oculocutaneous albinism, known as c.1441 C>T or A481T. However, it should be noted that there are still conflicts of interpretation about its pathogenicity, so if this mutation is present, the data should be interpreted with caution and based on symptomatology. The c.1441 C>T variant reduces the protein's function to 70%, causing a moderate form of the disease when found in compound heterozygosis with another pathogenic variant. In homozygosis c.1441 C>T may not be deleterious.
Type 2 oculocutaneous albinism genetic testing analyzes the 10 most frequent pathogenic mutations of the OCA2 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).
