The distinct effects of O-glycans on Notch receptors, coupled with differential expression of the relevant glycosyltransferases explain why different human diseases arise from mutation of POFUT1 (Dowling-Degos disease), LFNG (Spondylocostal Dysostosis) and EOGT (AOS) (Basmanav et al., 2014). This evidence concerns the gene POFUT1 and Dowling-Degos disease.