Elevated human tissue kallikrein levels in the stratum corneum and serum of peeling skin syndrome-type B patients suggests an over-desquamation of corneocytes.

TO THE EDITOR Peeling skin syndrome type B (PSS-type B, MIN 270300) is a congenital skin disease associated with continual skin peeling and ichthyotic erythroderma, known to display various clinical similarities with Netherton syndrome (NS, caused by genetic defects of serine protease inhibitor Kazal-type5 (SPINK5), MIN 256500) (Wile, 1924; Traupe, 1989; Magert et al., 1999; Chavanas et al., 2000). Human tissue kallikreins are a family of 15 trypsinor chymotrypsin-like secreted serine proteases (hK1–hK15) found in a variety of tissues (Yousef and Diamandis, 2001). At least eight different hKs have been identified in the stratum corneum (SC) and sweat as desquamation-related proteases (Komatsu et al., 2005b, 2006). Here, we aimed (1) to clarify the pathogenesis of PSS-type B, (2) to elucidate the relationship between PSS-type B and hK expression, and (3) to explain the reason for the clinical similarities between PSS-type B and NS. Informed consent was obtained from all patients, their parents, and normal volunteers, and our studies were performed according to the Declaration of Helsinki Principles. The Medical Ethics Committee of the Graduate School of Medical Science, School of Medicine, Kanazawa University and Juntendo University, School of Medicine, approved all described studies. Two unrelated 8-year-old female Japanese patients (Patient M and Patient K) were studied (Figure S1 and Table S1). Patients M and K were born with erythroderma accompanied by scaling and their lesions have shown no improvement to date. Patient M suffered significant growth retardation (o 2 SD) since the age of 1 and occasional herpes simplex infections in her perioral region. Both patients experience severe pruritus, temperature instability, and low sweat secretion. Patient M exhibited overabsorption of topical agents from skin, which is also observed in NS (Smith et al., 1995; Allen et al., 2001). Asthma attacks were experienced in Patient M but no allergic diseases were apparent in Patient K. Both patients displayed eosinophilia and elevated serum IgE levels. As many clinical manifestations observed in the patients are common between NS and PSS-type B (Traupe, 1989; Judge et al., 1994; Griffiths et al., 1998), SPINK5 gene mutation analysis by genomic polymerase chain reaction and sequencing was performed for both patients using specific primers (Komatsu et al., 2002). However, no gene mutations were detected in both patients; therefore, NS was ruled out, leaving PSS-type B as the most likely diagnosis. Pathologically, the patients showed an absence of the SC or a few layers of parakeratosis, which tended to be separated from the stratum granulosum, psoriasisforme acanthosis, and perivascular infiltration with mononuclear leukocytes (Figure S2). Immunohistochemistry for hK6, hK8, hK13, and SPINK5 protein showed that they were mainly expressed in the stratum granulosum and SC in normal epidermis (Figure 1). In both patients, the hKs and SPINK5 protein expressions were similarly distributed, and their stainings were deeply expanded into the lower epidermis compared with those in normal skin. It is known that the skin of NS patients shows absent or only faint staining against the same antiSPINK5 protein antibody (Raghunath et al., 2004). Consequently, Patients M and K are unlikely to suffer from NS. In the SC of both Patients M and K, all hK concentrations studied by ELISA were dramatically higher than those in the normal SC samples (Table 1a). The elevation of minor skin hKs (e.g., hK10, hK6, and hK13; o1.0 ng/mg dry weight for normal subjects) were prominent in the SC of the patients (Table 1a). In the serum, hK6, hK7, hK8, hK10, and hK13 concentrations were significantly elevated in the patients (Table 1b). SC trypsin-like serine protease enzymatic activity examined using BocPro-Phe-Arg-AMC (PFR-) as a substrate, and plasmin-like (for Boc-Val-Leu-LysAMC; VLK-) and furin-like (for PyrArg-Thr-Lys-Arg-AMC; R-KR-) activities were significantly elevated, whereas trypsin-like (for Boc-Phe-Ser-Arg-AMC; FSR-) and chymotrypsin-like (for MeOSuc-Arg-Pro-Tyr-pNA-HCl; RPY-) activities showed only mild elevations in both patients (Table 1c). Abbreviations: AMC, 7-amino-4-methyl-commarin; hK, kallikrein protein; NS, Netherton syndrome; pNA, para-nitroanilide; PSS, peeling skin syndrome; SC, stratum corneum; SPINK5, serine protease inhibitor Kazal-type 5