Oculocutaneous Albinism Type I (TYR gene, Burmese 2)
Specific alterations in the TYR gene, which regulates melanin production, can cause reduced pigmentation in areas of the body. These changes are also associated with oculocutaneous albinism type I.
Definition
Type I oculocutaneous albinism in the Burmese breed is characterized by a uniform mocha (light brown) coat along with seawater-colored eyes and pink nose and plantar pads. This condition is caused by mutations in the TYR gene, which encodes the enzyme tyrosinase, crucial for melanin production. Deficiency of this enzyme prevents melanin synthesis, causing lack of coloration in some areas.
Genetic basis
The C locus in the TYR gene determines coat coloration. At this locus there is the following allelic series: C > c^b = c^s > c, c^2. The C allele corresponds to the wild-type allele that produces melanin. In this case, we analyzed the c^m allele that causes a characteristic coloration pattern due to the c.820_936delinsAATCTC alteration in the TYR gene. The c^m variant is recessive for the C locus, although the interactions with the c^b and c^s alleles are still unclear. This trait is inherited in an autosomal recessive manner, which means that it requires the presence of two copies of the genetic variant for expression of the phenotype. Cats that have only one copy of this variant will not show the trait, but can transmit the allele to their offspring with a 50% probability.
Other relevant information
Other alleles of the same C locus are associated with other characteristic coats: the C allele allows normal melanin production, the c allele causes complete absence of coloration, while the c^b (Burmese cat) and c^s (Siamese cats) alleles reduce melanin production, creating specific color patterns. Although the TYR gene is related to oculocutaneous albinism, in this case this mutation does not cause complete albinism but hypopigmentation.
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