The overall objective of the STAIR Consortium is to study a group of diseases bound by common biochemistry, impact on health, and rarity. These diseases are all caused by impaired sterol or isoprenoid metabolism and include Smith-Lemli-Opitz Syndrome (SLOS), Sjögren-Larsson Syndrome (SLS), Hyperimmunoglobulinemia D with Periodic Fever Syndrome (HIDS), Sitosterolemia, and Cerebrotendinous Xanthomatosis (CTX). In five years, the STAIR Consortium will conduct several clinical studies, support a full-scale training program in the field of sterol and isoprenoid diseases, and engage several PAGs in consortium activities. In summary, the STAIR Consortium will foster multidisciplinary clinical research, promote training and education and support projects to explore promising leads in the understanding, diagnostics, and treatment of sterol and isoprenoid diseases.