Updated allele frequencies of SERPINB7 founder mutations in Asian patients with Nagashima-type palmoplantar keratosis/keratoderma

History and prospects of Nagashima-type palmoplantar keratosis, the most common palmoplantar keratoderma in east Asian populations

Nagashima-type palmoplantar keratosis (NPPK) has been shown to represent a form of autosomal recessive palmoplantar keratosis due to biallelic pathological variants of SERPINB7, which encodes a serine protease inhibitor expressed in the epidermis. Approximately 10 years have elapsed since NPPK was demonstrated to be an independent genetic disease, and the most prevalent palmoplantar keratoderma (PPK) in East Asian countries due to a high prevalence of founder mutations in SERPINB7. Since then, it has become evident that biallelic pathological variants of SERPINA12, which encodes a serine protease inhibitor expressed in the epidermis, can also manifest symptoms analogous to those of NPPK. Furthermore, a pathological variant of SERPINB7 was identified as a risk factor for the development of atopic dermatitis in a genome-wide association study (GWAS) of atopic dermatitis, indicating that the frequent co-occurrence of NPPK and atopic dermatitis is not a mere coincidence. Despite the documentation of NPPK cases in Japan since the 1970s, there have been no reports of individuals with similar symptoms from other regions, including Europe and the USA. Consequently, the existence and independence of the disease remained uncertain until its genetic cause was identified. The disease's independence was established through the accumulation of data on affected individuals, including the provision of accurate descriptions of their symptoms, which enabled the identification of the genetic cause. This review presents a comprehensive overview of the history and prospects of NPPK with a particular focus on the history of the process of establishing NPPK as an independent disease.

Nagashima-type palmoplantar keratoderma: Case series and two novel variants

Nagashima-type palmoplantar keratoderma (PPK) is an autosomal recessive PPK. We report four patients, highlight two new genetic variants, and emphasize the possibility of misdiagnosing the condition. Concomitant atopic dermatitis, specifically, may make correct diagnosis challenging. Clinicians should consider the diagnosis of Nagashima-type PPK in patients presenting with mild PPK with transgrediens and understand the importance of individualized multimodal treatment regimens.

Investigation of Nagashima-type palmoplantar keratoderma in China: A cross-sectional study of 234 patients

Nagashima-type palmoplantar keratoderma (NPPK) is the most prevalent hereditary palmoplantar keratoderma (PPK) in China, but there is a paucity of epidemiological data on the Chinese population. To explore the clinical and genetic characteristics, evaluate the demographic distribution, and estimate the burden of disease of NPPK. A total of 234 Chinese patients with NPPK were enrolled from two medical centers and an online PPK support group. Next-generation sequencing and Sanger sequencing were performed to screen out and confirm pathogenic mutations in SERPINB7. Clinical features and quality of life (QOL) were evaluated using self-completed questionnaires. In total, 14 pathogenic mutations were identified in SERPINB7 from the cohort. The top four recurrent mutations were c.796C>T (355, 75.9%), c.522dupT (66, 14.1%), c.650_653delCTGT (24, 5.1%), and c.455G>T (12, 2.6%), accounting for 97.6% of Chinese NPPK patients. Other mutations (11, 2.4%) include c.455-1G>T, c.336+2T>G, c.635delG and seven novel mutations c.2T>C, c.434delG, c.455-16A>G, c.656T>C, c.745-553T>G, c.832C>T, c.1036G>T. The estimated prevalence of NPPK in China was found to be 0.975/10 000 based on Chinese databases. Clinically, there were no apparent genotype-phenotype correlations in NPPK patients. Pediatric patients mainly presented with palmoplantar peeling, while adults presented with scale (p < 0.001). The most common comorbidities in NPPK patients were onychomycosis (40.0%), eczema (36.8%), and tinea pedis (30.3%). As for burden of disease, NPPK patients' QOL was decreased by a moderate degree. In this study, pathogenic mutations' allele frequencies in SERPINB7 were updated, and prevalence of NPPK in China was estimated. This large-scale cohort study provides evidence-based recommendations for patient management. Identification of new mutations are important for timely diagnosis of NPPK. Palmoplantar peeling in children can be used as a hallmark for early recognition of NPPK.

SERPINB7 mutation causes Nagashima-type palmoplantar keratosis and its spatiotemporal expression in zebrafish

Serine protease inhibitor B7 (SERPINB7) mutations have been reported to cause Nagashima-type palmoplantar keratosis (NPPK), but their biological effects are largely unknown. We conducted whole-exome sequencing and identified a c.796C>T (p.Arg266Ter) mutation in SERPINB7 in a Chinese pedigree, which presented as an autosomal recessive inheritance pattern. We assessed the function of SERPINB7 in homozygous and heterozygous mutation carriers, and the results suggested that the single c.796C>T mutation may alter the subcellular localization of SERPINB7. One of the homozygous mutation patients (II-3) was treated with ixekizumab and showed moderate improvement in keratinization. In addition, we analysed the spatiotemporal expression of serpinb1l1 and serpinb1l3, the zebrafish homologue of human SERPINB7, which is expressed in larvae and adults. In larvae, both serpinb1l1 and serpinb1l3 were expressed in the digestive tract. Then, we performed RT-PCR on adult fins based on similarity to the site of NPPK expression in humans and found that the genes were expressed in five fins (pectoral, pelvic, dorsal, anal and caudal) of the zebrafish distal extremity. Taken together, our results demonstrated that the single c.796C>T (p.Arg266Ter) mutation may alter the location of SERPINB7-encoded protein in the skin, while zebrafish SERPINB7 homologue was expressed in adult fins. These findings will enable us to construct knock-out models to explore the pathogenesis of palmoplantar keratosis.

Ceramide profiling of stratum corneum in Sjögren-Larsson syndrome

BACKGROUND

Sjögren-Larsson syndrome (SLS) is a neurocutaneous disorder whose causative gene is the fatty aldehyde dehydrogenase ALDH3A2 and of which ichthyosis is the major skin symptom. The stratum corneum contains a variety of ceramides, among which ω-O-acylceramides (acylceramides) and protein-bound ceramides are essential for skin permeability barrier formation.

OBJECTIVES

To determine the ceramide classes/species responsible for SLS pathogenesis and the enzymes that are impaired in SLS.

METHODS

Genomic DNA was collected from peripheral blood samples from an SLS patient and her parents, and whole-genome sequencing and Sanger sequencing were performed. Lipids were extracted from stratum corneum samples from the SLS patient and healthy volunteers and subjected to ceramide profiling via liquid chromatography coupled with tandem mass spectrometry.

RESULTS

A duplication (c.55_130dup) and a missense mutation (p.Lys447Glu) were found in the patient's ALDH3A2 gene. The patient had reduced levels of all acylceramide classes, with total acylceramide levels at 25 % of healthy controls. Reductions were also observed for several nonacylated ceramides: ceramides with phytosphingosine or 6-hydroxysphingosine in the long-chain base moiety were reduced to 24 % and 41 % of control levels, respectively, and ceramides with an α-hydroxy fatty acid as the fatty acid moiety were reduced to 29 %. The fatty acid moiety was shortened in many nonacylated ceramide classes.

CONCLUSION

These results suggest that reduced acylceramide levels are a primary cause of the ichthyosis symptoms of SLS, but reductions in other ceramide classes may also be involved.