Oculocutaneous albinism (OCA) is a group of autosomal recessive disorders characterised by hypopigmentation in the skin, hair and eyes due to disorders in the melanin biosynthesis. There are different types of OCA in which OCA type 1 and type 2 (OCA1 and OCA2) are the most common. Defects in the tyrosinase gene (TYR) and the oculocutaneous albinism gene (OCA2 formerly known as the P-gene) are considered to be causes of OCA1 and OCA2, respectively.
The protein encoded by the OCA2 gene is the P protein, whereas the protein encoded by the TYR gene is tyrosinase. The tyrosinase protein is important during the initial steps of melanin production, while the P protein (OCA2) is a transporter protein. The OCA2 gene (24 exons) spans ~344 kb of genomic DNA and is located on 15q12-q13.1, 28 Mb from the p-telomere. The TYR gene (5 exons) spans ~118 kb of genomic DNA and is located on 11q14.3, 89 Mb from the p-telomere.
The P325-A2 probemix contains 26 probes for the OCA2 gene, including probes for all exons of the gene with the exception of exons 8 and 23. Furthermore, four probes are present in or near the common 2.7-kb deletion area. For the TYR gene one probe for each exon is included in the probemix with the exception of exon 5. In addition, 11 reference probes are included in this probemix, detecting several different autosomal chromosomal locations.
This SALSA® MLPA® probemix is designed to detect deletions/duplications of one or more sequences in the aforementioned genes in a DNA sample. Heterozygous deletions of recognition sequences should give a 35-50% reduced relative peak height of the amplification product of that probe. Note that a mutation or polymorphism in the sequence detected by a probe can also cause a reduction in relative peak height, even when not located exactly on the ligation site! In addition, some probe signals are more sensitive to sample purity and small changes in experimental conditions. Therefore, deletions and duplications detected by MLPA should always be confirmed by other methods. Not all deletions and duplications detected by MLPA will be pathogenic; users should always verify the latest scientific literature when interpreting their findings. We have no information on what percentage of defects in these genes is caused by deletions/duplications of complete exons. Finally, note that most defects in this gene are expected to be small (point) mutations which will not be detected by this SALSA® MLPA® test.