In summary, our reclassification offers several advantages: 1) identifying patients with severe HeFH where PCSK9 inhibitor should be very effective to reduce their LDL cholesterol; 2) clarifying that the presence of cutaneous xanthomas during infancy is the specific phenotype as HoFH (typical of severe); and 3) identifying the most severe patients complicated with supravalvular aortic stenosis in their childhood where the most intensive treatments should be considered during their infancy. This evidence concerns the gene PCSK9 and supravalvular aortic stenosis.