PISD and Liberfarb syndrome: For example, gain-of-function pathogenic variants in PTDSS1 coding phosphatidylserine synthase causes Lens-Majewski syndrome (OMIM # 151050) characterized by skeletal deformities and intellectual disability; similarly, pathogenic variants in PISD coding phosphatidylserine decarboxylase were associated with Liberfarb syndrome (OMIM # 618889), also characterized by skeletal deformities (31, 32).