早老素（英语：Presenilin ，又译为早老蛋白）是一族相关联的多跨膜蛋白充当了一部分的γ-分泌酶（作为催化剂）膜内蛋白酶复合物。

Presenilins are a family of related multi-pass transmembrane proteins which constitute the catalytic subunits of the gamma-secretase intramembrane protease complex. They were first identified in screens for mutations causing early onset forms of familial Alzheimer's Disease by Peter St George-Hyslop at the Centre for Research in Neurodegenerative Diseases at the University of Toronto, and now also at the University of Cambridge. Vertebrates have two presenilin genes, called PSEN1 (located on chromosome 14 in humans) that encodes presenilin 1 (PS-1) and PSEN2 (on chromosome 1 in humans) that codes for presenilin 2 (PS-2). Both genes show conservation between species, with little difference between rat and human presenilins. The nematode worm C. elegans has two genes that resemble the presenilins and appear to be functionally similar, sel-12 and hop-1.