To test this novel strategy, we created RPE1 and HEK293T cells expressing COG4 mutations COG4-G516R (Saul-Wilson syndrome) and COG4-R729W (COG-CDG type IIj) under the endogenous COG4 promoter. Here, COG4 is linked to microcephalic osteodysplastic dysplasia, Saul-Wilson type.