In the control retina, single Ki67-positive cells were detected in the GCL (Supplementary Fig. 2y, z and Fig. 4k, l), whereas a significantly higher percentage of positive cells was detected in the sheet-like growing compartment of RBS lesions (p = 0.0003, Supplementary Fig. 2ac, ad and Fig. 4m, n). Here, MKI67 is linked to Roberts-SC phocomelia syndrome.