The MBTPS1 gene, which is located on chromosome 16q24, encodes the membrane-bound transcription factor protease site-1 (MBTPS1), commonly referred to as site-1 protease (S1P). S1P can process a variety of substrates independently or in conjunction with membrane-bound transcription factor protease site-2 (MBTPS2, also known as S2P), including sterol regulatory element binding proteins (SREBPs), activating transcription factor 6 (ATF6) and cyclic-AMP responsive element‑binding protein 3 (CREB3). Variants in the MBTPS1 gene can lead to multiple clinically distinct disorders with different phenotypes, including spondyloepiphyseal dysplasia of Kondo-Fu type (SEDKF), Cataract, alopecia, oral mucosal disorder, and psoriasis-like (CAOP) syndrome, and Silver-Russell-like syndrome (SRS). This review presents the structural and functional characteristics of S1P, enumerates the relevant substrates and elucidates the spectrum of associated disorders resulting from pathogenic variants of MBTPS1, and discusses the correlations investigates the genotype-phenotype correlations underlying these distinct clinical manifestations.