A Sporadic Case of Mal de Meleda Caused by Gene Mutation in SLURP-1 in Korea

Identification of a novel compound heterozygous mutation and a homozygous mutation of SLURP1 in Chinese families with Mal de Meleda

BACKGROUND

Mal de Meleda is an autosomal recessive palmoplantar keratoderma, with SLURP1 identified as the pathogenic gene responsible. Although over 20 mutations in SLURP1 have been reported, only the mutation c.256G > A (p.G87R) has been detected in Chinese patients. Here, we report a novel heterozygous SLURP1 mutation in a Chinese family.

METHODS

We assessed the clinical manifestations of two Chinese patients with Mal de Meleda and collected specimens from the patients and other family members for whole-exome and Sanger sequencing. We used algorithms (MutationTaster, SIFT, PolyPhen-2, PROVEAN, PANTHER, FATHMM, mCSM, SDM and DUET) to predict the pathogenetic potential of the mutation detected. We also employed AlphaFold2 and PyMOL for protein structure analysis.

RESULTS

Both patients displayed the typical manifestation of palmoplantar keratoderma. In Proband 1, we detected a novel compound heterozygous mutation (c.243C > A and c.256G > A) in exon 3 of SLURP1. Proband 2 was an adult female born to a consanguineous family and carried a homozygous mutation (c.211C > T). Algorithms indicated both mutations to be probably disease causing. We used AlphaFold2 to predict the protein structure of these mutations and found that they cause instability, as shown by PyMOL.

CONCLUSIONS

Our study identified a novel compound heterozygous mutation (c.243C > A and c.256G > A) in a Chinese patient with Mal de Meleda that has the potential to cause instability in protein structure. Moreover, this study expands on the existing knowledge of SLURP1 mutations and contributes to knowledge of Mal de Meleda.

Abnormal keratinization and cutaneous inflammation in Mal de Meleda

Mal de Meleda (MDM) is a rare, autosomal recessive form of palmoplantar keratoderma due to mutations in the gene, encoding for secreted lymphocyte antigen 6/urokinase-type plasminogen activator receptor related protein 1 (SLURP1). We report a four-year-old Taiwanese MDM female case whose biopsy specimen of hyperkeratotic lesions showed abnormal keratinization and cutaneous inflammation with characteristic transmission electron microscopic (TEM) findings and immunostaining results. The patient presented with pruritic and severely hyperkeratotic plaques on the bilateral palms and soles whichwere fringed with erythematous scaly areas. A homozygous c.256 G>A mutation, predicting a conversion of p.Gly86Arg, in SLURP1gene was detected. Histopathological examinations showed marked hyperkeratosis, acanthosis and hypergranulosis in the epidermis, accompanied by perivascular lymphocytic infiltrates in the dermis. The whole layers of the epidermis and perivascular infiltrates of the dermis were stained positive with anti-tumor necrosis factor alpha (TNFα) antibody in the biopsy specimen from the sole and the ankle. TEM examination of the biopsy specimen from the plantar hyperkeratotic plaque showed various-sized vacuoles surrounding nuclei of many keratinocytes in the spinous layer. In addition, there were numerous irregular keratohyaline granules in the granular layer. Several microorganisms and many lipid-like droplets were found in the thickened cornified layer. SLURP1 protein is known as a marker of late differentiation, predominantly expressed in the granular layer, and also known to have an inhibitory effect on TNFα release. Our results exhibited excessive TNFα expression in keratinocytes and perivascular infiltrates of the dermis, and several characteristic morphological observations of keratinocytes in MDM.

Patient with Mal de Meleda in whom a Novel Gene Mutation was Identified

Mal de Meleda, also known as keratoderma palmoplantaris transgrediens, is a rare type of autosomal recessive palmoplantar keratoderma. A 19-year-old male presented with a congenital yellowish discoloration and thickening of both palms and soles of the feet. His family history revealed that there was no consanguinity between the mother and the father and that the patient had three healthy brothers. The second- and third-degree relatives, five females and one male, also exhibited similar skin findings. From the isolated DNA samples, the extrinsic regions of the SLURP1 gene were screened using the sequence analysis and the Sanger sequencing was performed with the 3130 Sequence Analyzer. Results of this analysis show that a p.Arg 96 Pro (R96P) (c.287 CGA>CCA) homozygous missense point mutation was detected on the SLURP 1 (a secreted toxin-like mammalian lymphocyte antigen 6/urokinase-type plasminogen activator receptor-related protein 1) gene of the patients, while heterozygous p.Arg 96 Pro (R96P) (c.287 CGA>CCA) mutation was detected in the mother, father, and brothers. Our search of the Human Genome Mutation Database and previous literature revealed no reports of this mutation in mal de Meleda. We report this case due to the identification of a novel gene mutation in a patient with mal de Meleda, a palmoplantar keratoderma.

Mal de Meleda: A Focused Review

Mal de Meleda is a rare autosomal recessive palmoplantar keratoderma (PPK) disease with an estimated prevalence of 1:100,000. Clinically, the onset of the disease is typically soon after birth and features a transgrediens (plantar surface progressing to dorsal surface) and progrediens (worsening with age) pattern of hyperkeratosis of the palms and soles. The disease can feature other potentially disfiguring effects on the hands and feet that can severely impact function. Histologically, the lesions show hyperkeratosis and acanthosis without epidermolysis in the epidermis, accompanied by perivascular lymphocytic infiltrate in the dermis. Secreted LY6/urokinase-type plasminogen activator receptor (uPAR)-related protein-1 (SLURP-1) genetic mutations are implicated in Mal de Meleda. SLURP-1 is involved in mediation of inflammation as well as keratinocyte apoptosis regulation. Because the disease is so rare, there are no set guidelines for management, but the accepted approach tends to include oral acitretin plus topical keratolytic therapy. Genetic counseling should also be offered. This focused review highlights the clinical and histological features, differential diagnoses, genetic background, and the current thoughts on management of Mal de Meleda.

Palmoplantar keratoderma along with neuromuscular and metabolic phenotypes in Slurp1-deficient mice

Mutations in SLURP1 cause mal de Meleda, a rare palmoplantar keratoderma (PPK). SLURP1 is a secreted protein that is expressed highly in keratinocytes but has also been identified elsewhere (e.g., spinal cord neurons). Here, we examined Slurp1-deficient mice (Slurp1^−/−) created by replacing exon 2 with β-gal and neo cassettes. Slurp1^−/− mice developed severe PPK characterized by increased keratinocyte proliferation, an accumulation of lipid droplets in the stratum corneum, and a water barrier defect. In addition, Slurp1^−/− mice exhibited reduced adiposity, protection from obesity on a high-fat diet, low plasma lipid levels, and a neuromuscular abnormality (hind limb clasping). Initially, it was unclear whether the metabolic and neuromuscular phenotypes were due to Slurp1 deficiency because we found that the targeted Slurp1 mutation reduced the expression of several neighboring genes (e.g., Slurp2, Lypd2). We therefore created a new line of knockout mice (Slurp1X^−/− mice) with a simple nonsense mutation in exon 2. The Slurp1X mutation did not reduce the expression of adjacent genes, but Slurp1X^−/− mice exhibited all of the phenotypes observed in the original line of knockout mice. Thus, Slurp1 deficiency in mice elicits metabolic and neuromuscular abnormalities in addition to PPK.

Particular Mal de Meleda phenotypes in Tunisia and mutations founder effect in the Mediterranean region

Mal de Meleda (MDM) is a rare, autosomal recessive form of palmoplantar keratoderma. It is characterized by erythema and hyperkeratosis of the palms and soles that progressively extend to the dorsal surface of the hands and feet. It is caused by mutations in SLURP-1 gene encoding for secreted mammalian Ly-6/uPAR-related protein 1 (SLURP-1). We performed mutational analysis by direct sequencing of SLURP-1 gene in order to identify the genetic defect in three unrelated families (families MDM-12, MDM-13, and MDM-14) variably affected with transgressive palmoplantar keratoderma. A spectrum of clinical presentations with variable features has been observed from the pronounced to the transparent hyperkeratosis. We identified the 82delT frame shift mutation in the SLURP-1 gene in both families MDM-12 and MDM-13 and the missense variation p.Cys99Tyr in family MDM-14. To date, the 82delT variation is the most frequent cause of MDM in the world which is in favour of a recurrent molecular defect. The p.Cys99Tyr variation is only described in Tunisian families making evidence of founder effect mutation of likely Tunisian origin. Our patients presented with very severe to relatively mild phenotypes, including multiple keratolytic pits observed for one patient in the hyperkeratotic area which was not previously reported. The phenotypic variability may reflect the influence of additional factors on disease characteristics. This report further expands the spectrum of clinical phenotypes associated with mutations in SLURP1 in the Mediterranean population.