MBTPS2 and keratosis follicularis spinulosa decalvans: Genetic variants in MBTPS2 lead to three related genodermatoses in human patients: ichthyosis follicularis, atrichia, and photophobia (IFAP, OMIM #308205, Oeffner et al. 2009), Olmsted syndrome/palmoplantar keratoderma (OLMSX, OMIM #300918, Haghighi et al. 2013), and keratosis follicularis spinulosa decalvans (KFSDX, OMIM #308800, Aten et al. 2010).