Correlation between SPINK5 Gene Mutations and Clinical Manifestations in Netherton Syndrome Patients

Netherton syndrome (NS) is a congenital ichthyosiform dermatosis caused by serine protease inhibitor Kazal-type 5 (SPINK5) mutations. Tissue kallikreins (KLKs) and lymphoepithelial Kazal-type-related inhibitor (LEKTI) (SPINK5 product) may contribute to the balance of serine proteases/inhibitors in skin and influence skin barrier function and desquamation. SPINK5 mutations, causing NS, lead to truncated LEKTI; each NS patient possesses LEKTI of a different length, depending on the location of mutations. This study aims to elucidate genotype/phenotype correlations in Japanese NS patients and to characterize the functions of each LEKTI domain. Since we were unable to demonstrate truncated proteins in tissue from patients with NS, we used recombinant protein to test the hypothesis that the length of LEKTI correlated with protease inhibitory activity. Genotype/phenotype correlations were observed with cutaneous severity, growth retardation, skin infection, stratum corneum (SC) protease activities, and KLK levels in the SC. Predominant inhibition by LEKTI domains against overall SC protease activities was trypsin-like (Phe-Ser-Arg-) activity by LEKTI domains 6-12, plasmin- and trypsin-like (Pro-Phe-Arg-) activities by domains 12-15, chymotrypsin-like activity by all domains, and furin-like activity by none. KLK levels were significantly elevated in the SC and serum of NS patients. These data link LEKTI domain deficiency and clinical manifestations in NS patients and pinpoints to possibilities for targeted therapeutic interventions.