TP63 Mutations Research Articles

Facial clefting in Tp63 deficient mice results from altered Bmp4, Fgf8 and Shh signaling

During embryogenesis, the transcription factor Tp63 is expressed in the basal cells of multiple epithelial tissues. In humans, mutations in TP63 have been identified in five distinct human developmental disorders that are characterized by limb abnormalities, ectodermal dysplasia, and facial anomalies. To dissect the molecular pathogenesis of the bilateral cleft lip and cleft palate that results from mutation of Tp63, we analysed Tp63 mutant mice. At E10.5, Tp63-deficient mice exhibited abnormal morphogenesis of the medial nasal, lateral nasal and maxillary processes. Analysis of key signaling molecules revealed that these defects result from increased Bmp4 signaling in the epithelia of the facial processes. Acting antagonistically on Fgf8 and Shh, this aberrant signaling led to a reduction in mesenchymal cell proliferation and increased cell death in specific regions of the facial processes. In addition, a proliferative defect in the mesenchyme of the maxillary processes at E11.5 resulted in absence of the anterior region of the palatal shelves and, subsequently, cleft palate. Our results are consistent with a role for Tp63 in the regulation of Bmp signaling controlling the growth, modelling and fusion events underlying facial development and shed new light on the complex abnormality of facial clefting.

A new mutation in TP63 is associated with age-related pathology

Increases in the number of allelic malformation syndromes have led to their classification according to their pathogenesis rather than their clinical specific phenotype. TP63 (also known as TP73L) mutations have been identified in several such syndromes characterized by autosomal dominant transmission and various combinations of ectodermal dysplasia, limb malformations and orofacial clefting. TP63 has not yet been implicated in early aging phenotype in humans, even though p63 activates a program of cellular senescence and p63-compromised mice display features of accelerated aging. We report on a family with four affected adult females presenting with Rapp-Hodgkin syndrome (RHS), an autosomal dominant clinical entity that associates anhidrotic ectodermal dysplasia with cleft lip and palate. Features between RHS and EEC syndrome (ectrodactyly, ectodermal dysplasia and cleft lip/palate) have led to the recent identification of mutations in the TP63 gene, located on 3q27, in this condition. Our patients present typical clinical features of RHS, but also ophthalmic anomalies such as corneal dystrophy and premature menopause (around 30 years). The latter findings have never been reported in this condition, and could be secondary to a new TP63 deletion that has been identified in this family.

EEC syndrome, Arg227Gln TP63 mutation and micturition difficulties: Is there a genotype–phenotype correlation?

We report on two unrelated families with EEC syndrome (ectrodactyly, ectodermal dysplasia, cleft lip/palate), each with an Arg227Gln TP63 gene mutation, where the phenotype overlapped extensively with the allelic disorder, limb-mammary syndrome (LMS). Features common to both families were an ectodermal dysplasia principally affecting tooth, breast and nipple development, dacryostenosis and severe micturition difficulties. Additional findings included post-axial digital hypoplasia, cleft uvula, anal stenosis, hypoplasia of the perineal body and biopsy-proven interstitial cystitis. No individual had cleft lip. Split hand-split foot malformation (SHFM) occurred in one child-born after the molecular diagnosis was established. Unlike previous reports, the urinary symptoms were refractory to treatment with oral Fibrase and persisted into adulthood. Of the six cases/families now reported with EEC syndrome and Arg227Gln TP63 mutation, four have manifested this distinct urological abnormality, indicative of a genotype-phenotype correlation.

Frequency of genomic rearrangements involving the SHFM3 locus at chromosome 10q24 in syndromic and non‐syndromic split‐hand/foot malformation

Split-hand/foot malformation (SHFM), or ectrodactyly, is characterized by underdeveloped or absent central digital rays, clefts of the hands and feet, and variable syndactyly of the remaining digits. SHFM occurs as both an isolated finding and a component of many syndromes. SHFM is a heterogeneous condition caused by multiple loci, including SHFM1 (chromosome region 7q21-q22), SHFM2 (Xq26), SHFM3 (10q24), SHFM4 (3q27), and SHFM5 (2q31). Mutations in TP63 at the SHFM4 locus are known to underlie both syndromic and non-syndromic forms SHFM, but the causes of most non-syndromic SHFM cases remain unknown. The recent identification of submicroscopic tandem chromosome duplications affecting the SHFM3 locus in seven families with non-syndromic SHFM has helped to further unravel the molecular basis of this malformation. In our ongoing studies of the SHFM3 locus in 44 additional cases of syndromic and non-syndromic SHFM, we have identified similar chromosome rearrangements in eight additional cases (18%), using pulsed-field gel electrophoresis (PFGE). We have also utilized real-time quantitative PCR (qPCR) to test for the duplications. Seven of the cases with rearrangements were non-syndromic. The current findings bring the total of SHFM3-associated cases with chromosome rearrangements to 15, which constitute 29% (15 of 51) of the cases screened to date. This includes 9 of 9 cases (100%) with known linkage to the SHFM3 locus, all of whom have non-syndromic SHFM, and 6 of 42 additional cases (14%), four of whom have non-syndromic SHFM. Thus, SHFM3 abnormalities underlie a substantial proportion of SHFM cases and appear to be a more frequent cause of non-syndromic SHFM than mutations in TP63.

Two Novel TP63 Mutations Associated With the Ankyloblepharon, Ectodermal Defects, and Cleft Lip and Palate Syndrome

Ankyloblepharon, ectodermal defects, and cleft lip and palate (AEC) syndrome is a rare autosomal dominant disorder caused by mutations in the sterile alpha motif region of TP63, a homologue of the tumor suppressor TP53. Recent structure-function studies have identified complexities in the genotype-phenotype correlation of the p63 syndromes. We report 2 sporadic cases of AEC syndrome in infants. Both patients demonstrated skin erosions with prominent scalp involvement. Histologic studies demonstrated mild basal layer vacuolization and rare dyskeratotic keratinocytes, with evidence of both acantholysis and cytolysis at the blister edge. Immunohistochemistry using anti-p63 monoclonal antibody demonstrated basal epidermal nuclear staining in both healthy control and patient tissue samples. Ultrastructural studies showed focal disruption of anchoring fibrils near the blister edge of one patient and normal desmosomes, hemidesmosomes, and basement membrane zone in the nonblistered skin of the other patient. The DNA analysis of each patient revealed 2 novel missense mutations in the TP63 gene that resulted in L514S and R555P amino acid substitutions within the sterile alpha motif region of the p63 protein. We report 2 novel TP63 mutations resulting in AEC syndrome. The R555P mutation is the most carboxy-terminal of all the reported AEC missense mutations of p63. The presence of skin fragility, manifested as erosive skin lesions in body areas in addition to the scalp, is postulated to be an important diagnostic feature of AEC syndrome.

The Rapp-Hodgkin syndrome results from mutations of the TP63 gene.

The Rapp-Hodgkin syndrome (RHS, MIM 129400) corresponds to a rare form of anhydrotic ectodermal dysplasia, which shares some features with the ectrodactyly, ectodermal dysplasia and cleft lip/palate syndrome (EEC, MIM 604292) resulting from TP63 mutations. We report here, in two unrelated patients with RHS, the identification of two distinct TP63 mutations, corresponding to a novel frameshift mutation (1709DelA, exon 14) located downstream the sterile alpha motif (SAM) domain and to a missense mutation (R279H, exon 7) within the DNA binding domain. Functional analysis of the R279H mutation, which had previously been reported in several EEC families, shows that this mutation disrupted the dominant negative activity of the DeltaNp63alpha and gamma isoforms on the transcriptional activity of TP53. This report shows, on a molecular basis, that RHS is also an EEC-like syndrome resulting from mutations of the TP63 gene, and highlights the wide phenotypic spectrum associated to TP63 mutations.