PTDSS1 and primary bone dysplasia with increased bone density: Indeed, gain-of-function pathogenic variants in PTDSS1 coding PS synthase cause sclerosing bone dysplasia and intellectual disability (Lens-Majewski syndrome; OMIM # 151050), and pathogenic variants in PISD1 coding PS decarboxylase cause Spondyloepimetaphyseal dysplasias (31, 32).