Pathogenic MBTPS2 variants also cause (1) IFAP syndrome, characterized by the clinical triad of ichthyosis, photophobia, and atrichia (Oeffner et al., 2009); (2) keratosis follicularis spinulosa decalvans (KFSD), characterized by hyperkeratosis predominantly of the palms and soles, photophobia, and sparse hair (Aten et al., 2010); (3) Olmsted syndrome, characterized by mutilating palmoplantar keratoderma and alopecia (Haghighi et al., 2013); and (4) osteogenesis imperfecta (OI), characterized by fragile bones and recurrent fractures (Lindert et al., 2016). The gene discussed is MBTPS2; the disease is osteogenesis imperfecta.