Researchers at King’s College London, UK have reported that 192,986 European participants, across 10 populations, have identified 124 independent associations arising from 61 discrete genomic regions, including 50 previously unidentified for eye colour. The study suggests that 53.2% of eye colour variation explains using common single-nucleotide polymorphisms (SNPs). Researchers commented that “the genetic complexity of human eye colour considerably exceeds previous knowledge and expectations, highlighting eye colour as a genetically highly complex human trait”. A lead researcher in the study, Dr. Pirro Hysi at King’s College, as reported in GenomeWeb(www.genomeweb.com), stated that, “by describing [new] genes related to eye colour, we are identifying other genes that can potentially be the cause of cases of optic disc and retinal abnormalities that have previously remained unexplained and were not understood”.
Researchers have outlined that eye colour generally determines the ratio of two forms of melanin – eumelanin and pheomelanin – in addition to light absorption and scattering to give irises their colour. The eumelanin : pheomelanin ratio are higher in brown colour, while blue or green colour have little of the both pigments, and relatively more pheomelanin. Iris colour is well known to be heritable and the prevalence of blue eyes “correlates with geographic latitude across Europe and neighbouring areas, likely as a result of human migration, sexual, and possibly natural selection”. In their current study, UK researchers conducted the largest eye colour GWAS to date (genome wide association study) involving 192,986 European participants from 10 populations, as well as 1,636 Asian participants (of Han Chinese and Indian ancestry).
The findings of the study collectively explained 53.2% (95% CI, 45.4 – 61.0%) of eye colour variation using common SNPs, a total of 11,532,091 SNPs from 157,485 individuals of European ancestry. In addition to the current SNPs and eleven (11) previously known eye colour genes, there were fifty (50) novel eye colour–associated genetic loci which potentially “explains previously missing heritability of eye colour variability in European populations”. Researchers accept that further additional studies will be required to understand and unravel the science on how melanin biology works and how melanin metabolism may impact on the development of the optic disc and the development of the retina, including other gaps of knowledge awaiting.