At least four forms of OCA and one of OA are known, associated with TYR (OCA1), OCA2 (OCA2), TYRP1 (OCA3), SLC45A2 (OCA4) and GPR143 (OA1) loci, respectively.
Those genes include agouti signalling protein (ASIP), tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), oculocutaneous albinism II (OCA2), various solute carrier genes and transporters.
Blood samples were collected from 23 probands and 13 affected family members from 23 genetically unrelated Indian families (22 diagnosed as OCA and 1 diagnosed as OA) and analyzed by bidirectional DNA sequencing of the classic OCA genes--tyrosinase (TYR, or oculocutaneous albinism IA), pink eyed dilution (P; or oculocutaneous albinism II (OCA2]), tyrosinase-related protein 1 (TYRP1), solute carrier family 45, member 2 (SLC45A2; or membrane-associated transporter protein [MATP])--and the OA1 gene, G protein-coupled receptor 143 (GPR143).
Remarkably, this heterologous expression system recapitulates the defective processing and mistrafficking of tyrosinase observed in OCA2 albino melanocytes and certain amelanotic melanoma cells.
We studied the tyrosinase and P genes in three patients with type II oculocutaneous albinism, one of whom also had Prader-Willi syndrome, and in one patient with a milder syndrome known as autosomal recessive ocular albinism.
In addition, we report a mutation in both copies of the human P gene in one case of tyrosinase-positive (type II) oculocutaneous albinism, recently linked to 15q11-q13 (ref.9).
We therefore propose that the molecular basis for the development of tyrosinase-positive oculocutaneous albinism exists as a defect in other proteins required for the activation of tyrosinase or in other regions of the tyrosinase gene.
(1978) to also obtain a genetical classification, supported by the hairbulb test, has not proved to be useful for the classification of tyrosinase negative (TNOCA), tyrosinase positive oculocutaneous albinism (TPOCA), and autosomal recessive ocular albinism (AROA) as genetically distinct forms.