NCJ Number
246420
Journal
Forensic Science International: Genetics Volume: 7 Issue: 5 Dated: September 2013 Pages: 508-515
Date Published
September 2013
Length
8 pages
Annotation
In this study, we present a new objective method for measuring the eye colour on a continuous scale that allows researchers to associate genetic markers with different shades of eye colour.
Abstract
In this study, we present a new objective method for measuring the eye colour on a continuous scale that allows researchers to associate genetic markers with different shades of eye colour. With the use of the custom designed software Digital Iris Analysis Tool DIAT, the iris was automatically identified and extracted from high resolution digital images. DIAT was made user friendly with a graphical user interface. The software counted the number of blue and brown pixels in the iris image and calculated a Pixel Index of the Eye PIE-score that described the eye colour quantitatively. The PIE-score ranged from -1 to 1 brown to blue. The software eliminated the need for user based interpretation and qualitative eye colour categories. In 94% 570 of 605 analyzed eye images, the iris region was successfully extracted and a PIE-score was calculated. A very high correlation between the PIE-score and the human perception of eye colour was observed. The correlations between the PIE-scores and the six IrisPlex SNPs HERC2 rs12913832, OCA2 rs1800407, SLC24A4 rs12896399, TYR rs1393350, SLC45A2 rs16891982 and IRF4 rs12203592 were analyzed in 570 individuals. Significant differences p < 10 -6 in the PIE-scores of the individuals typed as HERC2 rs12913832 G PIE = 0.99 and rs12913832 GA PIE = -0.71 or A PIE = -0.87 were observed. We adjusted for the effect of HERC2 rs12913832 and showed that the quantitative PIE-scores were significantly associated with SNPs with minor effects OCA2 rs1800407, SLC24A4 rs12896399 and TYR rs1393350 on the eye colour. We evaluated the two published prediction models for eye colour IrisPlex 1 and Snipper 2 and compared the predictions with the PIE-scores. We found good concordance with the prediction from individuals typed as HERC2 rs12913832 G. However, both methods had difficulties in categorizing individuals typed as HERC2 rs12913832 GA because of the large variation in eye colour in HERC2 rs12913832 GA individuals. With the use of the DIAT software and the PIE-score, it will be possible to automatically compare the iris colour of large numbers of iris images obtained by different studies and to perform large meta-studies that may reveal loci with small effects on the eye colour.