We confirmed that three Chinese pedigrees affected with EEC or AEC harboring a distinct TP63 mutation, and described novel clinical phenotypes of EEC and AEC, including the presence of cubitus valgus deformity and taurodontism, which were discordant to their classical disease features.
Tumor protein p63 (TP63)-related disorders can be divided into at least six categories, including ectrodactyly-ectodermal dysplasia-cleft lip/palate syndrome 3 (EEC syndrome 3), ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC syndrome), acro-dermo-ungual-lacrimal-tooth syndrome (ADULT syndrome), limb-mammary syndrome (LMS), Rapp-Hodgkin syndrome (RHS) and split-hand/foot malformation 4 (SHFM4), and are all a result of heterozygous mutations of TP63.
Here, we show that multiple AEC-associated p63 mutations, but not those causative of other diseases, lead to thermodynamic protein destabilization, misfolding, and aggregation, similar to the known p53 gain-of-function mutants found in cancer.
Collectively, advancement in understanding the molecular mechanisms by which epidermal cell junctions precisely exert their functions and how p63 orchestrates their coordinated expression, will ultimately lead to insight into developing future strategies for the treatment of AEC syndrome and more in generally for diseases that share an overlapping phenotype.
For example, it has been postulated that reduced desmosomal protein expression occurs in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC), a skin fragility disorder caused by mutations in the transcription factor TP63.
The third hallmark of the EEC syndrome is orofacial clefting, in particular lip and palate. p63 mutations also cause the other five inherited syndromes: symptoms are overlapping, but each of these diseases has its own characteristic phenotypic features: for instance AEC syndrome (ankyloblepharon-ectodermal defects-cleft lip/palate) has as distinctive feature ankyloblepharon, while mammary glands and nipples hypoplasia are frequent findings in LMS syndrome and in ADULT syndrome (acro-dermato-ungual-lacrimal-tooth syndrome).
Mutations in TP63, mainly missense in exons 13 and 14 encoding the sterile alpha motif (SAM) and the transactivation inhibitory (TI) domains, account for 99% of mutations in individuals with AEC syndrome.
ADULT syndrome is much less common than the more classical forms of TP63-associated ectodermal dysplasias, such as ectrodactyly-ectodermal dysplasia-cleft lip/palate (EEC) syndrome and ankyloblepharon-ectodermal defects-cleft lip/palate syndrome.
These findings establish a functional link between FGF signalling and p63 in the expansion of epithelial progenitor cells and provide mechanistic insights into the pathogenesis of AEC syndrome.
Here, we characterize the transcriptional activity and protein stability of ΔNp63 mutants (that is, mutants of a p63 isoform that lacks the N-terminal transactivation domain) that are found in ectrodactyly-ectodermal dysplasia-cleft syndrome (EEC), ankyloblepharon-ectodermal dysplasia-clefting syndrome (AEC) and nonsyndromic split-hand/split-foot malformation (SHFM).
Several missense and heterozygous frame shift mutations, encoded within exon 13 and 14 of the p63 gene, have been identified in the p63α SAM domain in patients suffering from ankyloblepharon-ectodermal dysplasia-clefting syndrome.
We present an infant with AEC syndrome due to a novel TP63 mutation (F552S), who demonstrated neonatal erythroderma followed by extensive depigmentation.
Since DeltaNp63alpha is the predominantly expressed TP63 isoform in postnatal skin, we hypothesized that mutant DeltaNp63alpha proteins are primarily responsible for skin fragility in AEC patients.
These findings demonstrate that distinct AEC TP63 mutants can differentially compromise expression of downstream targets, providing a rationale for the variable spectra of symptoms seen in AEC patients.