FTX and microphthalmia: Because Ftx deficiency has a small effect on genome-wide gene expression in male mice, we propose that functional loss of Ftx causes a failure in the proper silencing of genes on the inactive X chromosome, which directly or indirectly can lead to downregulation of genes involved in eye development and eventually to microphthalmia in a subset of females homozygous or heterozygous for the Ftx mutation (Supplementary Fig. 12).