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RESEARCH REPORT |
1 Department of Pediatric Dentistry, Faculty of Dentistry, Chiang Mai University, Chiang Mai 50200, Thailand;
2 Department of Cell and Molecular Pathology, St Johns Institute of Dermatology, The Guys, Kings College and St Thomas Hospitals Medical School, St Thomas Hospital, Lambeth Palace Road, London SE1 7EH, UK;
3 Department of Dermatology, Kurume University School of Medicine, 67 Asahimachi, Kurume, Fukuoka 830-0011, Japan; and
4 Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Chiang Mai University, Chiang Mai 50200, Thailand;
*corresponding author, dnpdi001{at}chiangmai.ac.th
| ABSTRACT |
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KEY WORDS: AEC syndrome dental anomalies palmoplantar keratoderma p63 gene Rapp-Hodgkin syndrome
| INTRODUCTION |
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Nevertheless, RHS does display some clinical overlap with other ectodermal dysplasia syndromes, notably Ectrodactyly-Ectodermal Dysplasia-Clefting (EEC) syndrome (OMIM 129900) and Ankyloblepharon-Ectodermal Dysplasia-Clefting (AEC), also known as Hay-Wells syndrome (Hay-Wells Syndrome, OMIM 106260) (van Bokhoven and McKeon, 2002). Differentiating features of AEC and RHS appear to be the presence of ankyloblepharon in AEC and microsomia in RHS, but making an accurate diagnosis on clinical grounds alone may be difficult. Indeed, this was highlighted in a case of a woman with RHS whose son had features of EEC syndrome (Moerman and Fryns, 1996). The affected child also had ankyloblepharon, a component of AEC syndrome. Other overlap syndromes have also been reported (Cambiaghi et al., 1994; Rowan, 1996), suggesting that perhaps there might be a common genetic pathology to many of these and other related ectodermal dysplasia syndromes. It is noteworthy that some parents with AEC syndrome had affected children without ankylobleparon. Furthermore, the ankyloblepharon of some affected individuals is so subtle or friable at birth that it often goes unrecognized, and these cases may subsequently be diagnosed as RHS.
The molecular basis of most cases of EEC syndrome has recently been shown to involve mutations in the p63 gene (Celli et al., 1999). The majority of mutations is comprised of heterozygous missense changes in the DNA-binding domain of p63 (van Bokhoven et al., 2001). Moreover, AEC syndrome has subsequently been reported to result from missense mutations in p63, specifically within the sterile alpha motif (SAM) (McGrath et al., 2001). Thus, both these disorders are caused by heterozygous germline mutations in p63, and a genotype-phenotype correlation for the site of the mutation (DNA-binding domain or SAM domain) has been defined. To date, no pathogenetic mutations in p63 have been reported in patients with RHS. Therefore, in this study we investigated the molecular basis of RHS to further examine the possibility of allelic heterogeneity.
| MATERIALS & METHODS |
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Skin Biopsy
Following informed consent, a 4-mm punch biopsy was taken from the patients palm while he was under general anesthetic (given for dental surgery). Skin was fixed in 10% formalin and processed for routine light microscopy with paraffin-embedding. Five-micron sections were stained with hematoxylin and eosin and photographed.
| RESULTS |
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sequence [Yang et al., 1998], GenBank accession no. AF075430). The mutation converted a serine residue (TCC) to proline (CCC) and was designated S545P (Fig. 3
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| DISCUSSION |
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In addition to disclosing the initial p63 gene mutation in RHS, our study reports the first histological assessment of the erosive palm- and sole-skin thickening that is a characteristic feature of RHS. TP63 is known to have an important role in the regulation of epidermal stem cell proliferation (Schultz et al., 1997; Mills et al., 1999; Parsa et al., 1999; Yang et al., 1999; de Laurenzi et al., 2000), and its expression in keratinocytes has been used to distinguish stem cells from transit amplifying cells and other keratinocytes (Pellegrini et al., 2001). The missense mutation S545P in the p63 SAM domain clearly perturbs normal epidermal differentiation and maturation, leading to acanthosis (thickening) and hyperkeratosis (increased scale) as well as focal impairment of keratinocyte cell-cell attachment and, most notably, numerous apoptotic keratinocytes (colloid bodies). TP63 is known to influence keratinocyte apoptosis (Yang et al., 1998) in response to certain stimuli such as ultraviolet irradiation (Liefer et al., 2000) and in response to knockout mutations (Flores et al., 2002), but inhibition of apoptosis appears to be abrogated in the presence of the heterozygous missense mutation S545P. Analysis of these clinico-pathological data may therefore provide insight into one of the functions of the p63 SAM domain in normal epithelial physiology. Specifically, our case demonstrates the first example of increased epidermal apoptosis in association with a human germline mutation in p63. This is clearly distinct from AEC syndrome, where no increase of apoptosis is observed (McGrath et al., 2001). Palmoplantar keratoderma and mixed hearing loss, found in our patient, have not been reported in other patients affected with RHS (van Bokhoven and Brunner, 2002). The novel finding of hypoplastic scapula might have been related to p63 mutation, or it might have been a coincidence.
The p63 mutation detected may also be relevant to our understanding of the dental pathology present in some ectodermal dysplasia syndromes. The present patient has unerupted premolar and taurodontism, i.e., large dental pulp and short roots, and although there are no previous reports of p63 expression in dental pulps, the findings in our patient give credence to the significance of p63 expression during dental development, since large pulp chambers are known to occur as a consequence of defective dentin formation in the dental pulp, a key role for normally functioning odontoblasts. This process is evidently disrupted in the RHS patient described here. The SAM domain mutation S545P, and its effects on oral mucosal development, may also be relevant to the pathogenesis of the patients glossy tongue and absence of lingual frenum and of sublingual caruncles, since these are the rare clinical features in other p63-related syndromes.
In summary, this case discloses the molecular basis of RHS and provides new clinico-pathological insight into the consequences of a specific p63 SAM domain mutation on epithelial development.
| ACKNOWLEDGMENTS |
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Received October 1, 2002; Last revision January 9, 2003; Accepted February 3, 2003
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