HTRA1 and CARASIL: Mammalian high temperature requirement protease A1 (HTRA1) is one of four HtrA serine protease family members [1, 2], having recently come into prominence by virtue of its predicted involvement in the genetic disorders age-related macular degeneration (AMD) [3, 4] and cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL) [5, 6].