ABCA4 and Menkes disease: The genetic heterogeneity of MD and CD/CRD has been replicated in all other studies e.g. in a French cohort of 96 CD/CRD patients screened with an NGS panel of 123 genes, Boulanger-Scemama et al.27 found likely causative variants in 62% of cases with the ABCA4 gene being again the most commonly affected (25.4%, 15 out of 59 solved cases) followed by GUCY2D (8.5%, 5/59), CRX and PROM1 (6.7%, 4/59 cases each).