NS is due to loss-of-function mutations in the SPINK5 gene and to the consequent lack of expression of its encoded protein LEKTI in the skin and all stratified epithelial tissues. Following the identification of the NS causative gene and protein, specific diagnostic tools have been developed, thus breaking up the challenge of distinguishing NS from other congenital ichthyoses with overlapping features, and from severe, early-onset forms of atopic dermatitis or psoriasis.