A novel heterozygous pathogenic frameshift deletion variant (exon1:c.58_80del:p.G20fs) was identified in the <i>SOX2</i> gene, which was confirmed by Sanger sequencing in both affected brothers and did not exist in healthy parents, indicating germline mosaicism.<h4>Conclusion</h4>Most SOX2 mutations known look to arise de novo in probands and are diagnosed through anophthalmia or microphthalmia. The gene discussed is SOX2; the disease is microphthalmia.