Autosomal Dominant Lamellar Ichthyosis Due to a Missense Variant in the Gene NKPD1

The identification of monogenic causes for cornification disorders has enhanced our understanding of epidermal differentiation and skin barrier function. Autosomal dominant lamellar ichthyosis is a rare condition, and ASPRV1 was the only gene linked to autosomal dominant lamellar ichthyosis to date. We identified a heterozygous variant (ENST00000686631.1:c.1372G>T, p.[Val458Phe]) in the NKPD1 gene in 7 individuals from a 4-generation German pedigree with generalized lamellar ichthyosis by whole-exome sequencing. Segregation analysis confirmed its presence in affected individuals, resulting in a logarithm of the odds score of 3.31. NKPD1 encodes the NKPD1 protein, implicated in the plasma membrane; its role in human disease is as yet unknown. Skin histology showed moderate acanthosis and compact orthohyperkeratosis, and the ultrastructure differed clearly from that in ASPRV1-autosomal dominant lamellar ichthyosis. Although NKPD1 mRNA expression increased during keratinocyte differentiation, stratum corneum ceramides exhibited no significant changes. However, affected individuals showed an elevated ratio of protein-bound ceramides to omega-esterified ceramides. This highlights NKPD1's role in autosomal dominant lamellar ichthyosis, impacting ceramide metabolism and skin lipid barrier formation, as demonstrated through functional characterization.