Novel homozygous deletion of the plakophilin-1 gene in a Chinese patient with ectodermal dysplasia-skin fragility syndrome

Ectodermal dysplasia-skin fragility (EDSF) syndrome is a rare autosomal recessive disease characterized by skin fragility, chronic cheilitis, palmoplantar keratoderma, abnormal hair growth and nail dystrophy. EDSF syndrome is caused by mutations in the PKP1 gene encoding plakophilin-1, which result in desmosomal abnormality and poor intercellular cohesion between epidermal cells. Herein, we report a novel homozygous deletion of the PKP1 gene in a Chinese boy with EDSF syndrome. Our study expands the database on PKP1 mutations and emphasizes the key role played by PKP1 in the structure and function of the epidermal desmosomes. In addition, we describe the ultrastructural changes of the curly hair in patients with EDSF syndrome for the first time.

Ectodermal dysplasia-skin fragility syndrome: Two new cases and review of this desmosomal genodermatosis

BACKGROUND

Desmosomes are intercellular cadherin-mediated adhesion complexes that anchor intermediate filaments to the cell membrane and are required for strong adhesion for tissues under mechanical stress. One specific component of desmosomes is plakophilin 1 (PKP1), which is mainly expressed in the spinous layer of the epidermis. Loss-of-function autosomal recessive mutations in PKP1 result in ectodermal dysplasia-skin fragility (EDSF) syndrome, the initial inherited Mendelian disorder of desmosomes first reported in 1997.

METHODS

To investigate two new cases of EDSF syndrome and to perform a literature review of pathogenic PKP1 mutations from 1997 to 2019.

RESULTS

Sanger sequencing of PKP1 identified two new homozygous frameshift mutations: c.409_410insAC (p.Thr137Thrfs*61) and c.1213delA (p.Arg411Glufs*22). Comprehensive analyses were performed for the 18 cases with confirmed bi-allelic PKP1 gene mutations, but not for one mosaic case or 6 additional cases that lacked gene mutation studies. All pathogenic germline mutations were loss-of-function (splice site, frameshift, nonsense) with mutations in the intron 1 consensus acceptor splice site (c.203-1>A or G>T) representing recurrent findings. Skin fragility and nail involvement were present in all affected individuals (18/18), with most cases showing palmoplantar keratoderma (16/18), alopecia/hypotrichosis (16/18) and perioral fissuring/cheilitis (12/15; not commented on in 3 cases). Further observations in some individuals included pruritus, failure to thrive with low height/weight centiles, follicular hyperkeratosis, hypohidrosis, walking difficulties, dysplastic dentition and recurrent chest infections.

CONCLUSION

These data expand the molecular basis of EDSF syndrome and help define the spectrum of both the prototypic and variable manifestations of this desmosomal genodermatosis.