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SHORT COMMUNICATION
Homozygous Nonsense Mutation and Additional Deletion of an Amino Acid in BPAG1e Causing
Mild Localized Epidermolysis Bullosa Simplex
Yinghong HE, Juna LEPPERT, Holger STEINKE and Cristina HAS*
Department of Dermatology, University Medical Center Freiburg, Hauptstrasse 7, DE-79104 Freiburg, Germany. E-mail: cristina.has@
uniklinik-freiburg.de
Accepted Jan 24, 2017; Epub ahead of print Jan 25, 2017
The bullous pemphigoid antigen 1 (BPAG1) is a
cytoskeletal linker protein connecting intermediate
filaments to the cell membrane. Alternative splicing
gives rise to multiple tissue isoforms with variable
expression in the skin, nervous system and muscles, and
a high functional complexity, which is poorly understood
(1, 2). The biological relevance of BPAG1 isoforms is
underscored by their association with human genetic and
acquired disorders (3).
The 230-kDa epidermal isoform, BPAG1e consists
of a coiled-coil rod domain flanked by globular NH 2 -
terminal head and COOH-terminal tail domains and was
first identified as the autoantigen in bullous pemphigoid
(1, 4). Recently 2 homozygous nonsense mutations,
p.Gln1124* and p.Arg1249* in the BPAG1 gene, dys-
tonin (DST) were reported in patients with a new sub-
type of autosomal recessive epidermolysis bullosa (EB)
simplex (5–7). Both mutations are located within the
coiled-coil rod domain of BPAG1e, which is involved in
homodimerization. The amino terminus is important for
the recruitment of BPAG1e into hemidesmosomes, while
the C-terminus binds to keratin intermediate filaments
(8). Loss of BPAG1e has been shown result in lack of
hemidesmosomal inner plaques in the skin (5, 6).
We describe here a patient with very mild skin fragility
associated with a previously unreported homozygous
nonsense mutation and homozygous deletion of an
amino acid in the coiled-coil rod domain of BPAG1e,
and reveal the consequences of these mutations in the
skin and epidermal keratinocytes.
MATERIALS AND METHODS ( see Appendix S1 1 )
CASE REPORT
The index case was a man who was first examined at the age of 19
years, when no blisters, but only plantar keratoderma was noted
(Fig. 1A). He reported having had recurrent skin blistering since
childhood, mainly following sporting activities, but was otherwise
healthy. His parents were related and originated from Turkey.
His father reported that he and his sister had skin blistering in
childhood, which alleviated after puberty. Initially, we suspected
autosomal dominant localized EB simplex, but mutations in the
keratin 5 and 14 genes were excluded. After being involved in a
fight, the patient presented again, with blisters on the hands (Fig.
1B), lower legs and feet, and a skin biopsy was obtained from a
https://www.medicaljournals.se/acta/content/abstract/10.2340/00015555-2618
1
fresh blister. Skin cleavage was noted in the basal epidermal layer,
and immunoreactivity for BPAG1e was negative in both blistered
and not blistered skin (Fig. 1E), indicating that skin fragility was
due to loss of this protein. Hence, sequencing of DST identified an
homozygous in-frame deletion in exon 17, c.2618_2620delAAG,
which leads to deletion of a glutamic acid residue, p.Glu873del,
and a homozygous transversion in exon 23, c.3805C>T, that
converts glutamine to a premature termination codon, designated
p.Gln1269* (Fig. 1C and D). The first variant is referenced in
databases (rs770713340) with a minor allele count of 0.00003/4,
while the latter has not been reported previously (ExAC, dbSNP,
HGMD professional).
Next, we examined the consequences of these mutations in
keratinocytes isolated from the patient’s skin. Morphologically
the patient’s keratinocytes demonstrated good spreading capacity
(Fig. S1A 1 ). The mutation did not lead to complete mRNA decay
(not shown), but BPAG1e was not detectable in keratinocytes
when using an antibody directed to the N-terminus (Fig. S1A 1 ).
The mRNA levels of collagen XVII were reduced and those of
focal adhesion components were upregulated (not shown). In
cultured keratinocytes, immunoreactivity for integrin α6 was
reduced and collagen XVII was reduced at the periphery of the
cells. Immunoblot analysis revealed that full-length collagen XVII
was increased (3.21-fold) in cell lysates, while the ectodomain
was decreased (0.61-fold) in cell culture media. Integrin β1 and
fibronectin were enhanced (Fig. S1 1 ). In line with this, immunoblot
analysis demonstrated an increase in vinculin (2.21-fold), kindlin-1
(2.22-fold) and 2 (2.44-fold) and fibronectin in the keratinocytes
of the patient compared with the control cells (Fig. S1B 1 ). Mo-
reover, the immunoreactivity, the protein and mRNA levels of
keratin 5, 14 and 15 appeared to be increased in the keratinocytes
of the patient compared with the control (Fig. S1 1 ). These results
suggest that lack of BPAG1e impacts the interconnected mole-
cular complexes, hemidesmosomes, focal adhesions and keratin
intermediate filaments.
DISCUSSION
Th