Since the protein sequence of mouse Eif2s3y is highly conserved (over 97% similarity) with those of mouse Eif2s3x and human X-linked EIF2S3, and there is no Y-linked homolog of Eif2s3y in humans (Supplementary Figures 7A,B), overexpression of Eif2s3y in male and female mice may partially resemble patients with Klinefelter Syndrome (47,XXY) and XXX Syndrome (47,XXX), respectively. Here, EIF2S3 is linked to Klinefelter syndrome.