The difficulties in using PCSK9 inhibitors in all patients with HoFH were borne out by results from the TESLA and TAUSSIG trials, which demonstrated that the PCSK9 inhibitor evolocumab had diminished activity in HoFH patients with negative functional mutations versus those with mutations allowing some residual LDL-R activity [22, 23]. The gene discussed is PCSK9; the disease is homozygous familial hypercholesterolemia.