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

Abstract

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.

Figure 1

Clinical manifestations of MDM. Pronounced yellowish erythematous transgrediens palmoplantar keratoderma over the hands and feet of patient belonging to family MDM-12 ((a)-(b)). Transparent hyperkeratosis with red border delimiting the hyperkeratotic area and multiple keratolytic pits in one patient belonging to family MDM-14 ((c)-(d)).

Figure 2

In silico modeling of the SLURP1 wild type (a) and SLURP1 with the p.Cys99Tyr mutation (b). The model shows the possible structural differences between the mutant and wild-type proteins. The presence of the p.Cys99Tyr variation led to a new protein folding missing the loops conformation. Structures are determined from amino acid sequences with I-Tasser online server and figures produced with PyMOL viewer. The p.Cys99Tyr variation position is showed by red.

Figure 3

Geographic distribution of the SLURP-1 gene reported mutations. Met1Lys (Emirates Bedouin [15]); Ivs1 + 1G > A (Pakistani [16]); Trp15Arg (German [15], Scottish [3], and Dutch [17]); 82delT (Tunisian [3], Scottish [3], Algerian [3], Croatian [9], Kurdish [10], and Italian [11]); Ivs2 + 1G > A (Algerian [3]); Cys43Stop (Turkish [18]); Arg71Pro (Dutch [17]); Cys77Ala (Tunisian [4]); Pro82Ser (Turkish [19]); Gly86Arg (Palestinian [15], Turkish [15]), and Pakistani [16]), Korean [20], Taiwanese [21]); Arg96Stop (Croatian [9], Turkish [10], Korean [20], and Pakistani [16]); Lys98Pro (Turkish [22]); Cys99Tyr (Tunisian [12]); and Arg71His (patient was reported in a study from France, and the origin is not reported [23]).