The SHG-to AF aging index of the dermis (SAAID) is defined as the difference between SHG and AF intensity signals, indicative of type I collagen and elastin, respectively, and normalized to the sum of both signals as follows [52,53,54,55,56]:SAAID = (SHG − AF)/(SHG + AF).(1). The gene discussed is ELN; the disease is atrial fibrillation.