The relative contribution of the X chromosome to ocular phenotypes

The X chromosome is unique, both in terms of functional expression and evolutionary history. Population frequencies for a minority of conditions, such as mental retardation, are directly related to the X chromosome. To explore these ideas, we investigated the general role of the X chromosome in ocular genetics through bioinformatic analysis of the distribution of eye-related genes in the human genome. The proportion of eye-disease loci located on the X chromosome compared to those eye diseases with an autosomal locus was calculated. The resultant figure (3.47) is lower than that calculated for mental retardation (9.74). A comparison between the number of X chromosome genes expressed in the eye compared to the number of autosomal genes expressed in the eye also did not reveal significant differences. Of all genes expressed in the eye, 2.9% are thought to be located on the X chromosome, fewer than found for the larger autosomes (which range from 10.1% to 3.6%). The eye's functional genetic components appear to be dispersed throughout the human genome, possibly to ensure survival in the event of significant cytogenetic derangement.