RARE DISEASES. A proposal for a clinical approach for EEC Syndrome
The EEC syndrome (Ectrodactyly-Ectodermal DysplasiaClefting) is a rare genetic disorder resulting from mutations in the p63 gene and characterized by ocular surface defects and also by ectrodactyly, ectodermal dysplasia and cleft lip and palate (1/1.000.000 in the Italian population). Patients develop progressive total bilateral limbal stem cell deficiency, which eventually results in corneal blindness. While in childhood clefting and hand deformities are the main clinical features, during early adulthood ocular problems become the predominant clinical aspect of EEC syndrome. Patients often show ocular surface alterations such as recurrent blepharitis and conjunctivitis, superficial microlesions of the cornea, spontaneous corneal perforation and ulceration, defective regeneration and poor reepithelialization following trauma or penetrating keratoplasty (PK). They are characterised by dense vascularized corneal pannus, leading to progressive corneal clouding and eventually severe visual impairment. Alterations leading to these symptoms are: (1) the atresia of the lacrimal duct system and the absence of meibomian glands causing tear film instability and (2) the epithelial defects of the cornea caused by mutations in the p63 gene. While tear film instability and dry eye symptoms can be overcome with tear supplements, no curative treatments are currently available for the epithelial defects.
The preliminary results of our research network (Fondazione Banca degli Occhi del Veneto and the Department of Molecular Medicine, University of Padova, based in Padova, Italy) suggest that the phenotypic effects of the mutations can be reverted, with optimal results if treatments are started at early ages (data published in international peer-reviewed journals: Stem Cells and Stem Cells Translational Medicine, 2016). Limbal stem cell deficiency (LSCD) can be caused either by primary genetic dysfunctions (as in the EEC syndrome) or be the result of acquired factors. Common therapeutic strategies, such as penetrating keratoplasty (PK) and even cell therapy strategies based on transplantation of autologous cultured limbal stem cells, cannot be a definitive cure, since p63 mutations severely compromise the ability of autologous stem cells to regenerate the corneal epithelium. Since LSCD in the EEC syndrome usually occurs in the 2nd-3rd decade and leads to severe corneal failure in the 4th to 5th decade, this provides a therapeutic window to correct the genetic defect using preventive strategies, which could maintain a clear cornea, prevent blindness and obviate pain and photophobia.
For patients carrying the R279H mutation, in the early phases of the disease when limbal epithelial stem cells are still present in the limbus, the use of eye drops containing mutant-specific siRNAs may be a practical therapeutic option. When LSCD is well established and no limbal stem cells are left, the corneal pathology may be improved by ex vivo gene correction of autologous cultured oral mucosa stem cells with p63 mutant-specific siRNAs. For the unique patient, homozygous for a novel and de novo R311K mutation in the p63 gene, and characterized from a somatic mosaicism (80% of homozygous mutant cells and 20% heterozygous cells), cultured autologous oral mucosal epithelial stem cell sheets obtained by selecting heterozygous R311K-p63 stem cells might become an effective therapy and bypass the need for gene therapy.
With this proposal, our goal is to move forward towards a clinical study and correcting the genetic defect using either preventive strategies (using eye drops containing siRNA molecules towards the p.R279H mutation) or a stem cell approach (for p.R311K mutation). If successful, our clinical approach could have a tremendous impact on the quality of life of EEC patients.
