To test whether the shRNA-mediated downregulation of MLH1 was reversible, cells from each subclone were split into two separate cultures, with one culture maintained in the presence of doxycycline to maintain MLH1 deficiency, and the other culture grown in the absence of doxycycline to allow MLH1 expression. Here, MLH1 is linked to hyperinsulinemic hypoglycemia, familial, 4.