While the use of siRNAs, the overexpression of kinase dead Rsk mutants or cells from Rsk2-deficient mice or from patients with Coffin–Lowry syndrome have been helpful, the simultaneous expression of the Rsk1, 2 and 3 in most cell types has complicated the study of their cellular functions. The gene discussed is RPS6KA1; the disease is Coffin-Lowry syndrome.