Here we described the clinical profile of nine patients (belong to seven different families) with Papillon-Lefèvre Syndrome (PLS), from the northwestern Mexican state of Sinaloa. They showed keratosis palmoplantaris and aggressive periodontitis with variable expression, which are the classical features of this syndrome . In contrast to the nearly 30% of consanguinity of PLS cases reported in different countries [2, 3], our PLS patients were born to non-consanguineous parents, and their families were not related.
PLS patients showed a DPPI activity reduction up to 85%, while parents and siblings showed a partial reduction of nearly 50%. This enzymatic deficiency was not due to diminished CTSC gene expression levels, as no significant differences were found between all groups. In agreement with our findings, more than 80% of all PLS cases reported show CTSC deficiency due to gene mutations [14, 34]. Zhang et al. found less than 10% of the normal enzymatic activity in PLS patients and 50% in parents . To our knowledge, there are no reports of CTSC messenger quantification using qPCR technique for this purpose in the literature.
Cases 2P and 4P were found to be compound heterozygous for c.203 T >; G and c.458C >; T, while all other cases were found to be homozygous for c.203 T >; G. Of note, all parents, as well as four siblings, carried either c.203 T >; G or c.458C >; T. These findings could explain the reduction in DPPI activity observed in these subjects, and seems to confirm the autosomal recessive mode of inheritance of PLS.
According to the Human Gene Mutation Database (HGMD), 77 variants of the CTSC gene have been reported. The c.203 T >; G substitution we report here, is a novel loss-of function mutation, and associates with the diminished enzymatic activity observed in our PLS patients. In accordance, frequency of allele G (c.203 T >; G) was higher in patients and relatives in comparison to population controls (all P ≤ 0.05).
The substitution c.458C >; T has been reported as both a common polymorphism in some populations, and as causal mutation in PLS patients [47–49]. c.458C >; T has been reported as causal mutation in one Australian PLS patient (compound heterozygous for c.458C >; T and c.199_222del) . However, a genotypic study for the c.458C >; T polymorphism in the Spanish population reported frequencies of 81% for homozygote normal and 19% for heterozygote . In accordance, allele T (c.458C >; T) was found relatively frequent in our population (9%), with no significant differences between the studied groups, and PolyPhen-2 software predicted a probably benign mutation. Therefore, the results of cases 2P and 4P remain inconclusive as the pathogenic variant other than c.203 T >; G remains unidentified in the coding region.
Some patients in this study showed increased susceptibility to bacterial skin infections. This condition seems to be due to an impairment of the immune system, which is involved in the pathoetiology of PLS. Therefore, we genotyped HLA class I and II alleles of PLS patients, their relatives and controls to evaluate any particular HLA association with this disease. We found fourteen HLA-A, twenty-nine HLA-B, twelve HLA-DRB1 and six HLA-DQB1 alleles (online Additional file 1), with HLA-A*02, B*35, DRB1*04, and DQB1*0301 being the most frequent in the population. A common HLA-A/B/DR/DP haplotype was not found in the families, confirming the lack of relationship among them.
With exception of HLA-DRB1*11, our results are in agreement with other reports showing no particular association of HLA alleles with PLS [32, 34]. We found that HLA-DRB1*11 allele was significantly more frequent (P = 0.0071) in our PLS patients than in controls (33.33% vs. 7.32%, respectively), resulting in an estimated relative risk index of 6.33. Interestingly, this allele has been also associated with scleroderma in Caucasian patients . HLA-A*24(9), HLA-B*35, DRB1*04 and DR51 showed higher frequency in our PLS patients than in controls, but the differences were not statistically significant. HLA-A*24(9) DRB1*04 and DR51 alleles have been associated with different kinds of periodontitis in other countries [33, 51–53].
Mexicans, Mestizos in general, have a high degree of genetic heterogeneity due to centuries of mixing with Native Americans, Africans and Europeans. In the South and Central parts of Mexico, the predominant HLA type is more Amerindian than European or African, but in Sinaloa, half of the most common HLA haplotypes are believed to be of European origin. Allelic frequencies of the population found in this work were in accordance with a previous report . An important difference is that our more extensive molecular study had included, for the first time, the side-by-side comparison of PLS families with unrelated, healthy controls.
Although the exact pathogenesis of PLS is still unknown, biochemical and genetic analysis allows for genetic counseling and opportune treatment, especially for those patients with familial history of this disease. Furthermore, some authors believe that if treatment is started at an early age, patients would possibly have normal adult dentition . One of the studied cases (7P) is only 18-months-old, and will be under treatment and observation to avoid serious complications.
While in México the general prevalence of this syndrome is still unknown, and the number of reported cases is very low, the finding so far of 20 patients in the state of Sinaloa highlights the need for more studies of this nature. Due to the concentrated number of PLS patients found in our population, none of them previously described, is would be possible to argue that there is a founder effect for CTSC gene mutation. An haplotype analysis of DNA markers in CTSC gene region can help to determine if c.203 T >; G mutation has this founder effect.