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Alejandra Young, Richard A Lewis, Debora B Farber; Screening the DNA of Ocular Albinism Patients for Possible Mutations in GNAI3 (Guanine Nucleotide Binding Protein, Alpha Inhibiting Activity Polypeptide 3 gene). Invest. Ophthalmol. Vis. Sci. 2014;55(13):6438.
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© ARVO (1962-2015); The Authors (2016-present)
Ocular albinism type 1 (OA) is the most common form of ocular albinism. It has an estimated prevalence of 1/50,000 in the general population of the United States. Although the cutaneous manifestations of OA are very mild, affected patients present abnormal, giant melanosomes in both the RPE and skin and show abnormal crossing of the optic axons at the brain optic chiasm. This disease is caused by mutations in the OA1 gene that encodes a G-protein coupled receptor, OA1, which in the eye is specifically localized to RPE melanosomal membranes. We have previously demonstrated by in-vivo and in-vitro studies on mice that the heterotrimeric G protein Gαi3 signals in the same transduction pathway controlled by Oa1 to regulate melanosomal biogenesis and axonal growth through the optic chiasm. Mutations in the OA1 gene in humans could render the OA1 protein incapable of activating the heterotrimeric Gαi3 on the surface membrane of the melanosome. The same effect would be observed in the absence of Oa1 or Gαi3 in the corresponding knockout mice. We hypothesized that the presence of macromelanosomes in the RPE of ocular albino patients in whom a mutation in OA1 had not been found, might be explained by mutations in GNAI3, the human ortholog of the mouse Gαi3 gene. Thus, the objective of this work was to screen the DNA of this type of OA patients.
DNA from 26 patients diagnosed with OA and presenting a phenotype consistent with the disease but who did not show mutation(s) in OA1 were tested for mutations in GNAI3. We sequenced the entire GNAI3 gene (~47Kb) using Agilent’s Haloplex Technology. Several primers were designed to amplify the coding region (9 exons), including its upstream 5’ UTR in boundary with the GPR61 gene, and its 3’ UTR bordering the MIR197 gene.
Agilent’s Haloplex sequencing of the 26 OA patients’ DNAs identified several new sequence variants in the 5’ and 3’ UTRs. However, 6 control subjects shared these variants.
Our results show that the sequence variants observed in the 5’ and 3’ UTRs of the GNAI3 gene from the 26 OA patients studied are common in normal humans and, therefore, cannot be the cause of the abnormal phenotype observed in their RPE.
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