[Nagashima-type palmoplantar keratoderma: A little-known palmoplantar keratoderma in Europe]

Herein we present a case of palmoplantar keratoderma (PPK) in a young adopted girl of Chinese origin living in France.

The patient, aged six years, had presented transgressive PPK since birth, as well as erythema progressing in congestive inflammatory episodes, palmoplantar hyperhidrosis and progressive characteristics (moderate hyperkeratosis in areas of rubbing other than the palms and soles, namely the elbows and knees). Histopathological examination of a skin biopsy revealed a thick epidermis with lengthening and thickening of crests. The epithelium displayed a thick granular layer. Electron microscopy showed hyperorthokeratosis with hypergranulosis and loss of lamellar structure of the keratinosomes, as well as cleavage between corneocytes. Molecular studies showed the presence of two composite heterozygous mutations of the SERPINB7 gene, enabling a diagnosis of Nagashima-type PPK (NPPK) to be made.

NPPK is an autosomal recessive disease caused by a mutation in the SERPINB7, a member of the superfamily of serine protease inhibitors. It was described by Nagashima in 1977 with molecular characterisation by Kubo following in 2013. It is the most widespread form of PPK in Asia (with a prevalence of 1.2/10,000 in Japan and 3.1/10,000 in China). It is distinguished from the other PPKs in terms of transgressive soft hyperkeratosis, inflammatory episodes and hyperhidrosis, as well as by its non-progressive nature. In the present case, while the clinical presentation was characteristic, diagnosis was only made thanks to sequencing of a panel of over 50 genes responsible for PPK. The disease is effectively little-known in Europe. This study highlights the increasing importance of diagnostic investigation methods involving the use of gene panels.