Split-hand/split-foot malformation with paternal mutation in the p63 gene

Case report: Prenatal diagnosis of Ectrodactyly-Ectodermal dysplasia-Cleft syndrome (EEC) in a fetus with cleft lip and polycystic kidney

Ectrodactyly-ectodermal dysplasia-cleft (EEC) syndrome is an autosomal dominant disorder characterized by ectrodactyly, ectodermal dysplasia, and orofacial clefting. Reduced penetrance is manifested in these core features and additional under-recognized features, especially in prenatal cases. Here, we present a fetus with EEC syndrome at 22 weeks gestation, in which the cleft lip and palate and the right polycystic kidney are shown by prenatal ultrasound. A de novo missense mutation of R304W in the TP63 gene is confirmed by whole-exome sequencing associated with EEC syndrome. We further investigate the reported TP63-related prenatal cases and provide a more complete picture of the prenatal phenotypic spectrum about EEC. It illustrates the potential severity of genitourinary anomalies in TP63-related disorders and highlights the need to counsel for the possibility of EEC syndrome, given the occurrence of genitourinary anomalies with orofacial cleft or limb deformities.

DLX5, FGF8 and the Pin1 isomerase control ΔNp63α protein stability during limb development: a regulatory loop at the basis of the SHFM and EEC congenital malformations

Ectrodactyly, or Split-Hand/Foot Malformation (SHFM), is a congenital condition characterized by the loss of central rays of hands and feet. The p63 and the DLX5;DLX6 transcription factors, expressed in the embryonic limb buds and ectoderm, are disease genes for these conditions. Mutations of p63 also cause the ectodermal dysplasia–ectrodactyly–cleft lip/palate (EEC) syndrome, comprising SHFM. Ectrodactyly is linked to defects of the apical ectodermal ridge (AER) of the developing limb buds. FGF8 is the key signaling molecule in this process, able to direct proximo-distal growth and patterning of the skeletal primordial of the limbs. In the limb buds of both p63 and Dlx5;Dlx6 murine models of SHFM, the AER is poorly stratified and FGF8 expression is severely reduced. We show here that the FGF8 locus is a downstream target of DLX5 and that FGF8 counteracts Pin1–ΔNp63α interaction. In vivo, lack of Pin1 leads to accumulation of the p63 protein in the embryonic limbs and ectoderm. We show also that ΔNp63α protein stability is negatively regulated by the interaction with the prolyl-isomerase Pin1, via proteasome-mediated degradation; p63 mutant proteins associated with SHFM or EEC syndromes are resistant to Pin1 action. Thus, DLX5, p63, Pin1 and FGF8 participate to the same time- and location-restricted regulatory loop essential for AER stratification, hence for normal patterning and skeletal morphogenesis of the limb buds. These results shed new light on the molecular mechanisms at the basis of the SHFM and EEC limb malformations.

Analysis of large phenotypic variability of EEC and SHFM4 syndromes caused by K193E mutation of the TP63 gene

EEC (ectrodactyly, ectodermal dysplasia, clefting; OMIM 604292) is an autosomal dominant developmental disorder resulting mainly from pathogenic mutations of the DNA-binding domain (DBD) of the TP63 gene. In this study, we showed that K193E mutation in nine affected individuals of a four-generation kindred with a large degree of phenotypic variability causes four different syndromes or TP63-related disorders: EEC, Ectrodactyly-ectodermal dysplasia (EE), isolated ectodermal dysplasia, and isolated Split Hand/Foot Malformation type 4 (SHFM4). Genotype-phenotype and DBD structural modeling analysis showed that the K193-located loop L2-A is associated with R280 through hydrogen bonding interactions, while R280 mutations also often cause large phenotypic variability of EEC and SHFM4. Thus, we speculate that K193 and several other DBD mutation-associated syndromes may share similar pathogenic mechanisms, particularly in the case of the same mutation with different phenotypes. Our study and others also suggest that the phenotypic variability of EEC is attributed, at least partially, to genetic and/or epigenetic modifiers.

Discrepancies in upper and lower limb patterning in split hand foot malformation

Discrepancies in upper and lower limb patterning in split hand foot malformation. Split hand foot malformation (SHFM) is genetically heterogeneous with five loci mapped to date. Highly variable in presentation, it can occur as an isolated finding or with other anomalies. The genetic heterogeneity and clinical variability make genetic counselling of SHFM families challenging. By establishing genotype/phenotype correlations, one can provide insight into responsible developmental genes and help to direct mapping efforts and target genetic testing, ultimately providing more accurate information for family members. Preaxial involvement of the upper extremities was a significant discriminating limb-specific variable in our analysis of genetically mapped SHFM cases. This finding, which was originally identified through descriptive epidemiology, was subsequently confirmed by discriminant function analysis (p < 0.0001) to be a significant locus discriminator. Preaxial involvement of the upper extremities was most commonly seen at the SHFM3 locus mapped to chromosome 10q24 (OMIM 600095) and consisted of proximally placed thumbs and/or triphalangeal thumbs (TPT), preaxial polydactyly and/or absence of the first ray. These patients' feet, however, tended to show a classical central longitudinal deficiency without a significant preaxial component. This article discusses this discrepant clefting pattern between the upper and lower extremities and proposes potential mechanisms.

Rubella virus infection dysregulates the pattern of p63 expression

The effect of rubella virus (RV) on the expression of the p63 isoforms was investigated in Vero cells. The levels of all the TAp63 isoforms were elevated, while the expression of a approximately 73 kDa isoform corresponding to DeltaNp63alpha was downregulated in Vero cells infected with the To-336 strain of RV. A approximately 66 kDa isoform corresponding to TAp63beta was the predominant protein species in RV-infected cells. Semi-quantitative end-point dilution RT-PCR analysis, with TAp63beta isoform-specific primers, detected a 4-fold rise in the TAp63beta mRNA level following virus infection. Taken together, our data demonstrate that RV infection alters the stoichiometric ratio of the p63 isoforms. The dysregulated pattern of p63 expression observed in RV-infected cells may represent a mechanism whereby RV exerts its pro-apoptotic effect.

p63 Gene mutations in eec syndrome, limb-mammary syndrome, and isolated split hand-split foot malformation suggest a genotype-phenotype correlation

p63 mutations have been associated with EEC syndrome (ectrodactyly, ectodermal dysplasia, and cleft lip/palate), as well as with nonsyndromic split hand-split foot malformation (SHFM). We performed p63 mutation analysis in a sample of 43 individuals and families affected with EEC syndrome, in 35 individuals affected with SHFM, and in three families with the EEC-like condition limb-mammary syndrome (LMS), which is characterized by ectrodactyly, cleft palate, and mammary-gland abnormalities. The results differed for these three conditions. p63 gene mutations were detected in almost all (40/43) individuals affected with EEC syndrome. Apart from a frameshift mutation in exon 13, all other EEC mutations were missense, predominantly involving codons 204, 227, 279, 280, and 304. In contrast, p63 mutations were detected in only a small proportion (4/35) of patients with isolated SHFM. p63 mutations in SHFM included three novel mutations: a missense mutation (K193E), a nonsense mutation (Q634X), and a mutation in the 3' splice site for exon 5. The fourth SHFM mutation (R280H) in this series was also found in a patient with classical EEC syndrome, suggesting partial overlap between the EEC and SHFM mutational spectra. The original family with LMS (van Bokhoven et al. 1999) had no detectable p63 mutation, although it clearly localizes to the p63 locus in 3q27. In two other small kindreds affected with LMS, frameshift mutations were detected in exons 13 and 14, respectively. The combined data show that p63 is the major gene for EEC syndrome, and that it makes a modest contribution to SHFM. There appears to be a genotype-phenotype correlation, in that there is a specific pattern of missense mutations in EEC syndrome that are not generally found in SHFM or LMS.