However, the distinctly lower penetrance of IBD in Turner syndrome compared with X-linked monogenic IBD defects in genes like CYBB, FOXP3, and WAS suggests a more complex genetic interplay.6,54–56 As the loss of one X chromosome or its parts has broad effects on gene expression across the whole genome, development of IBD and other autoimmune disease in patients with Turner syndrome could be due to cumulative gene dosage effects on multiple loci. This evidence concerns the gene CYBB and Turner syndrome.