Muscular dystrophy in a family of Labrador Retrievers with no

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Neuromuscular Disorders ■■ (2015) ■■–■■
www.elsevier.com/locate/nmd
Muscular dystrophy in a family of Labrador Retrievers with no muscle
dystrophin and a mild phenotype
Natassia M. Vieira a, Ling T. Guo b, Elicia Estrela a, Louis M. Kunkel a, Mayana Zatz c,
G. Diane Shelton b,*
a
The Division of Genetics and Genomics, Boston Children’s Hospital, Department of Pediatrics and Genetics, Harvard Medical School, Boston, MA 02115,
USA
b
Department of Pathology, School of Medicine, University of California San Diego, La Jolla, CA 92093
c
Human Genome and Stem Cell Center, Biosciences Institute, University of Sao Paulo, Brazil
Received 8 November 2014; received in revised form 24 February 2015; accepted 26 February 2015
Abstract
Animal models of dystrophin deficient muscular dystrophy, most notably canine X-linked muscular dystrophy, play an important role in
developing new therapies for human Duchenne muscular dystrophy. Although the canine disease is a model of the human disease, the variable
severity of clinical presentations in the canine may be problematic for pre-clinical trials, but also informative. Here we describe a family of
Labrador Retrievers with three generations of male dogs having markedly increased serum creatine kinase activity, absence of membrane
dystrophin, but with undetectable clinical signs of muscle weakness. Clinically normal young male Labrador Retriever puppies were evaluated
prior to surgical neuter by screening laboratory blood work, including serum creatine kinase activity. Serum creatine kinase activities were
markedly increased in the absence of clinical signs of muscle weakness. Evaluation of muscle biopsies confirmed a dystrophic phenotype with both
degeneration and regeneration. Further evaluations by immunofluorescence and western blot analysis confirmed the absence of muscle dystrophin.
Although dystrophin was not identified in the muscles, we did not find any detectable deletions or duplications in the dystrophin gene. Sequencing
is now ongoing to search for point mutations. Our findings in this family of Labrador Retriever dogs lend support to the hypothesis that, in
exceptional situations, muscle with no dystrophin may be functional. Unlocking the secrets that protect these dogs from a severe clinical myopathy
is a great challenge which may have important implications for future treatment of human muscular dystrophies.
© 2015 Elsevier B.V. All rights reserved.
Keywords: Myopathy; Canine; Animal model
1. Introduction
Duchenne muscular dystrophy (DMD) is a lethal X-linked
condition which affects 1 in 3500 to 5000 male births. It is
caused by mutations in the DMD gene, which result in the
absence of muscle dystrophin [1]. Without any intervention,
affected patients carrying a null mutation show a very similar
severe clinical course. The onset is usually noticed around 3–5
years of age with loss of ambulation between 9 and 12 years of
age. Death occurs in the second or third decade due to
respiratory or cardiac failure.
In contrast to the mdx mouse, the murine model of DMD
with a mild clinical phenotype despite the lack of muscle
dystrophin [2] but a reduced life-span [3], the Golden Retriever
* Corresponding author. Department of Pathology, School of Medicine,
University of California San Diego, La Jolla, CA 92093-0709, USA. Tel.: +1
858 534 1537; fax: +1 858 534 0391.
E-mail address: [email protected] (G.D. Shelton).
Muscular Dystrophy (GRMD) dog represents the best animal
model for DMD [2,4]. Affected founder animals carry a
frameshift mutation in the dystrophin gene that causes the
skipping of exon 7 and a premature stop codon, resulting in the
absence of dystrophin in their muscles [5]. GRMD dogs and
DMD patients have many phenotypic and biochemical
similarities including early progressive muscle degeneration
and atrophy, fibrosis, contractures and markedly elevated serum
creatine kinase (CK) activities. However, unlike humans,
GRMD dogs may have dysphagia and esophageal dysfunction,
but loss of ambulation is uncommon. Early death may occur
within the first weeks of life but is most frequently around 1–2
years of age as a result of respiratory failure or cardiomyopathy.
A striking feature of GRMD is the degree of phenotypic
variability that occurs as a result of dystrophin deficiency. We
have previously reported on a Brazilian GRMD dog colony
(Gene Dog) with an exceptional dog, Ringo, who showed a very
mild course despite the complete absence of muscle dystrophin
[6]. Ringo was born in 2003 and survived with good motor
http://dx.doi.org/10.1016/j.nmd.2015.02.012
0960-8966/© 2015 Elsevier B.V. All rights reserved.
Please cite this article in press as: Natassia M. Vieira, et al., Muscular dystrophy in a family of Labrador Retrievers with no muscle dystrophin and a mild phenotype, Neuromuscular
Disorders (2015), doi: 10.1016/j.nmd.2015.02.012
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N.M. Vieira et al. / Neuromuscular Disorders ■■ (2015) ■■–■■
2
function until 2014. Ringo had 49 offspring born from natural
intercourse with 4 different females. Among them, Suflair, born
in 2006, also shows a milder phenotype although more severe
than Ringo.
Dystrophin deficient muscular dystrophy in Labrador
Retriever dogs (LRMD) is another canine model of DMD. In the
first clinical report of LRMD in a male puppy, severe clinical
signs were described including dysphagia, weakness and
inspiratory stridor [7]. Clinical signs began in the immediate
postnatal period. Over the years 2002 to 2010, muscle biopsies
were submitted to the Comparative Neuromuscular Laboratory,
University of California San Diego (GDS) for pathological and
immunohistochemical diagnosis on 12 additional young, male
Labrador Retrievers. In all of these 12 cases, a dystrophic
phenotype was identified and clinical information described
moderate to severe generalized myopathic signs (Shelton,
unpublished). Generalized weakness and gait abnormalities
were present progressing to variable atrophy and hypertrophy of
different muscle groups including the diaphragm, esophagus and
pharyngeal muscles. Cardiomyopathy and respiratory
insufficiency resulted in early death or euthanasia. The serum
CK activities were markedly increased which helped
differentiate this form of muscular dystrophy from other
congenital myopathies affecting young Labrador Retriever
puppies such as centronuclear myopathy [8], X-linked
myotubular myopathy [9] and collagen VI deficiency [10]. A
mutation in the dystrophin gene has been described in severely
affected LRMD dogs with an insertion between exon 19 and 20
resulting in a premature stop codon [4].
In 2010 we evaluated a muscle biopsy from a young male
Labrador Retriever puppy for which markedly and persistently
increased CK activities were noted in the absence of clinical
signs of myopathy. Over the subsequent 4 years, we followed
this dog and the large family of related Labrador Retrievers
from the northeastern United States. All affected males had
markedly elevated serum CK activities but showed no obvious
clinical signs of myopathy. Dystrophin deficient muscular
dystrophy was confirmed in 12 male dogs from this family
evaluated by histopathology, immunohistochemistry and
western blot.
Here we describe the pathological, immunohistochemical
and western blot results on this family of clinically
asymptomatic Labrador Retrievers with dystrophin deficiency.
The elucidation of the mechanism that is protecting these
exceptions from the deleterious effect of the dystrophin gene
mutation is still unknown, but it could open new avenues for
human DMD future therapies. Our findings add additional
support to the observations that it is possible to have a
functional muscle in a large animal despite the absence of
muscle dystrophin, as previously reported in GRMD [6] and
recently described in humans [11].
2. Methods
2.1. Animals and archived tissues
All affected Labrador Retriever puppies evaluated in this
study were presented to general veterinarians for pre-surgical
screening prior to neuter. Physical examinations were
performed on all dogs. Routine blood evaluations including a
complete blood count (CBC) and serum biochemical profiles
with measurement of CK activity were performed in all dogs.
Unless indicated, muscle biopsies were performed at the time of
neuter for histopathologic diagnosis and immunostaining.
Archived frozen muscles from previously diagnosed severely
affected Labrador Retriever puppies and normal young dogs
were used for comparison in immunohistochemical studies.
Muscle from GRMD and normal Golden Retrievers from the
GRMD Genedog colony at the University of Sao Paulo, Brazil
were also used for comparison.
2.2. Histopathology and immunohistochemistry
Biopsies from the vastus lateralis or biceps femoris muscles
of affected Labrador Retrievers were collected under general
inhalational anesthesia and shipped by an overnight express
service under refrigeration to the Comparative Neuromuscular
Laboratory, University of California San Diego. Immediately
upon receipt, the biopsies were flash frozen in isopentane precooled in liquid nitrogen and stored at −80 °C until further
processed. All control muscles were similarly processed for a
direct comparison to the affected Labrador muscles. A standard
panel of histochemical stains and reactions was performed on
8 µm muscle cryosections [12]. Additional cryosections were
used for immunohistochemical stainings using antibodies
against the rod (1:100, NCL-DYS1, Novocastra Laboratory) and
carboxy terminus (1:100, NCL-DYS2 Novocastra Laboratories)
of dystrophin, α-sarcoglycan (1:200, gift from Eva Engvall),
β-sarcoglycan (1:100, NCL-βSG, Novocastra Laboratories) and
γ-sarcoglycan (1:100, NCL-γSG, Novocastra Laboratories),
laminin α2 (1:200, gift from Eva Engvall), utrophin (1:20,
NCL-DRP2, Novocastra Laboratories), developmental myosin
heavy chain (1:20, NCL-MHCd, Novocastra Laboratories),
dysferlin (1:50, NCL-hamlet, Novocastra Laboratories) and
spectrin (1:10, NCL-SPEC2, Novocastra Laboratories).
Stainings were visualized using immunofluorescent techniques
as previously published [13].
2.3. Western blot
Muscle sample proteins were extracted using RIPA buffer.
Samples were centrifuged at 13,000 g for 10 minutes to
remove insoluble debris. Soluble proteins were resolved by
6% SDS-PAGE, and transferred to nitrocellulose membranes
(Hybond; Amersham Biosciences). All membranes were
stained with Ponceau (Sigma-Aldrich) to evaluate the amount
of loaded proteins. Membranes were blocked for 1 hour in
Tris-buffered saline Tween (TBST) containing 5% powdered
skim milk and incubated overnight with the following primary
antibodies: anti-dystrophin NCL-DYS1 and NCL-DYS2
(1:1000, both from Novocastra Laboratories); 6–10 (1:1000)
[14] and AB15277 antidystrophin antibody (1:1000, Abcam).
Horseradish peroxidase (HRP)-conjugated secondary antibody
(1:1000, Santa Cruz Biotechnology) was used to detect bound
antibodies with enhanced chemiluminescence (ECL) plus kit
(GE Healthcare).
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2.4. PCR genotyping for the GRMD dog mutation
DNA from four of the affected Labrador Retriever dogs,
and affected and carrier dogs from the GRMD colony in
Brazil, were tested for the GRMD mutation as previously
described [15]. The cDNA region flanking the dystrophin
exon 7 was amplified using the following primers: ForwardGATTGCAACAAACCAACAGTG and Reverse-AACTCT
TTCAGTTGCTGATTCT and a 57 °C annealing temperature.
2.5. PCR genotyping for the LRMD dog mutation
DNA from two of the mildly affected Labrador Retriever
dogs, three severely affected dogs, a dog with GRMD and a
control dog from the GRMD colony in Brazil, were tested for the
LRMD mutation. The region flanking the 6363 bp insertion in
3
intron 19 of dystrophin gene was amplified using the following
primers: Forward-TGAAAGTAAGAGCTGAGTCATGG and
Reverse-TCGCCAAAAGTGAATTGAAA and a 60 °C
annealing temperature.
3. Results
3.1. Affected male Labrador Retrievers had markedly
elevated CK activities in the absence of clinical muscle
weakness
A 7 month old male Labrador Retriever puppy without
obvious clinical signs of muscular weakness, atrophy or other
medical problems was presented for pre-neuter screening
(Fig. 1A). No abnormalities were found on general physical and
neurological examination. Laboratory evaluations including
Fig. 1. (A) A seven month old male Labrador retriever puppy (dog 1 in panel B) with a markedly elevated CK activity, histopathologic phenotype consistent with
a muscular dystrophy, and the absence of muscle dystrophin. At the time of neuter there was no clinical evidence of a myopathy. (B) Pedigree showing relationships
of 3 generations of affected Labrador retriever dogs and obligate carriers.
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a CBC and serum biochemical analysis with CK activity
were performed. The CK activity was markedly increased
(>40,000 IU/L, reference <200 IU/L), and upon recheck one
week later, remained elevated (>30,000 IU/L). Because of the
markedly increased CK activities, biopsies were collected from
the vastus lateralis muscle at the time of neuter. Over the
following 2 years, muscle biopsies from 10 additional young
male Labrador Retriever puppies were submitted by general
veterinarians due to markedly elevated CK activities identified
prior to neuter or after identification of relatedness of all
11 dogs (Fig. 1B, pedigree). Muscle weakness, atrophy or
dysphagia was not noted in any of the additional dogs. A further
3 asymptomatic, related, male Labrador Retriever puppies with
markedly elevated CK activities and no clinical signs of
myopathy were also identified, but muscle biopsies were not
collected. All muscle biopsies, including that from the original
case were submitted by veterinarians in the Northeastern
United States.
3.2. Histopathology and immunohistochemistry showed a
dystrophic phenotype, absence of or greatly diminished
muscle dystrophin, and utrophin in regenerating fibers
Hematoxylin and eosin stained cryosections from the first
affected puppy (Puppy 1, Fig. 1B) confirmed degenerative and
regenerative changes consistent with a dystrophic phenotype
(Fig. 2). Degenerating fibers undergoing necrosis and
phagocytosis (Fig. 2Aa), groups of basophilic regenerating
fibers (Fig. 2Ab) and calcific deposits (Fig. 2Ac) were noted.
Immunohistochemical staining using an antibody against
developmental myosin heavy chain confirmed the presence of
Fig. 2. Representative cryosections from dog 1 in Fig. 1B stained with hematoxylin and eosin show the degenerative (a) and regenerative (b) changes typical of the
dystrophic phenotype (A). Calcific deposits were occasionally noted (c). Immunostains from additional affected dogs (dogs 6–10 in Fig. 1B) showed clusters of
regenerating fibers using an antibody against developmental myosin heavy chain. Bar in panel A(c) = 50 µm for all figures.
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Fig. 3. Representative fluorescence immunostaining showing results from dog 8 in Fig. 1B and control. Staining was undetectable using an antibody against the
rod-domain of dystropin. Rare presumptive revertant fibers were noted using an antibody against the carboxy-terminus of dystrophin. Utrophin staining was
increased in groups of myofibers and further investigated in Fig. 4. Staining for spectrin, α sarcoglycan and other dystrophin associated proteins (staining for β and
γ sarcoglycan not shown) was similar to control tissue. Bar = 50 µm for all images.
clusters of regenerating fibers in all dogs (Fig. 2B). Based on
histopathology from all 11 related dogs, a dystrophic myopathy
was diagnosed.
To further investigate a specific type of muscular dystrophy,
immunostaining of muscle cryosections was performed using
antibodies against dystrophin associated proteins as described
in methods. In general, staining was markedly diminished or
absent with antibodies against the rod domain and C-terminus
of dystrophin (Fig. 3). Rare presumptive revertant fibers (2–3
per 500 fibers) were observed. Stainings for all other dystrophin
associated proteins were similar to controls.
To further investigate the pattern of utrophin expression,
serial cryosections from mild and severely affected Labrador
Retrievers, and control muscle, were incubated with antibodies
against utrophin and developmental myosin heavy chain
(Fig. 4). Myofibers expressing utrophin were limited to
regenerating fibers in both the mild and severely affected
Labrador Retrievers. Neither sarcolemmal labeling of utrophin
nor staining of regenerating fibers were found in the control dog
muscle.
3.3. Dystrophin protein was absent using Western blot
analysis
To confirm the absence of dystrophin expression in the
muscles of LRMD dogs, we performed a Western blot analysis
(Fig. 5). Total muscle protein from LRMD dogs 8 and 15 were
compared with two GRMD dogs, and normal human samples.
The dystrophin band of 427 kDa was completely absent in
samples from dogs 8 and 15 as in the GRMD dogs, but was
present in normal amount in the control samples. No small
dystrophin bands with molecular weights below approximately
400 kDa were identified. Four different dystrophin antibodies
were used to confirm the findings: two against the rod-domain
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Retriever puppies (dogs 5 and 8 in Fig. 1B), 2 affected Golden
Retrievers, a Golden Retriever female carrier and a wild type
Golden Retriever. The affected Labradors did not carry the
same mutation found in GRMD dogs (Fig. 6A). The cDNA
region flanking the deleted exon of dystrophin in the GRMD
dog model was amplified from a LRMD dog and a normal
control. Bands of expected size were observed in both samples,
which showed no deletion (Fig. 6B).
3.5. Neither mildly or severely affected Labrador Retriever
dogs with dystrophin deficiency carried the LRMD Mutation
To verify whether these dogs carried the same dystrophin
mutation as previously reported in Labrador Retrievers with
LRMD [4], genotyping was performed using DNA from 2 of
the mildly affected Labrador Retriever puppies (dogs 8 and 15
in Fig. 1B), 3 severely affected LRMD dogs from the tissue
archives of the Comparative Neuromuscular Laboratory, a
GRMD dog from the Brazil colony and a normal dog (Fig. 6C).
Fig. 4. Representative fluorescence immunostaining of serial cryosections
from a mildly affected Labrador Retriever (dog 8 in Fig. 1B), a previously
diagnosed severely affected Labrador Retriever and a control dog using the
DRP2 antibody against utrophin and dMHC antibody to detect regenerating
fibers. The sarcolemma of regenerating fibers was positively stained while the
sarcolemma of non-degenerating fibers was unstained in both the mild and
severe cases. Sarcolemmal staining of control muscle was not detected. Nuclei
were highlighted with DAPI. Bar = 50 µm for all images.
Fig. 5. Dystrophin expression in the muscles of LRMD dogs (dogs 8 and 15 in
Fig. 1B), an affected Golden retriever (GR) and control dog and human muscle
was assessed by western blot. The dystrophin band of 427 kDa was completely
absent in the LRMD and GR dogs, but was present in the dog and human
control samples. Four different dystrophin antibodies were used to confirm the
findings. Beta-actin was used as a loading control.
(DYS-1 and 6–10) and two against the c-terminus region
(DYS-2 and AB15277 from Abcam).
3.4. Mildly affected Labrador Retrievers with dystrophin
deficiency do not carry the GRMD mutation
To verify whether these dogs carried the same dystrophin
mutation as Golden Retrievers with GRMD [6], genotyping
was performed using DNA from 2 of the affected Labrador
Fig. 6. LRMD dogs do not carry the same mutation as the GRMD dogs.
(A) PCR genotyping using DNA from four of the affected Labrador retriever
dogs (dogs 1, 5, 7 and 8 from Fig. 1B), and affected and carrier dogs from the
GRMD colony in Brazil confirmed the LRMD dogs did not carry the GRMD
mutation. (B) Amplification of dystrophin cDNA region flanking exon 7 shows
normal size bands (994 bp) in both a mildly affected LRMD dog (8) and normal
Labrador (Dog) including a negative water control (C). (C) Neither mildly
affected nor severely affected LRMD dogs carry the previously reported
dystrophin mutation since bands of expected size (460 bp) were observed. The
absence of the 6363 bp insertion in the intron 19 of dystrophin gene was
confirmed in samples from mildly affected LRMD dogs (8, 15) and severely
affected LRMD dogs (S) as compared to a GRMD dog (GR) and normal dog
(N).
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Bands of expected size were observed in all samples,
confirming the absence of the 6363 bp insertion.
4. Discussion
The identification of the dystrophin gene and its protein
product provided an explanation for the difference in severity
between DMD and its allelic form, Becker muscular dystrophy
[16]. While DMD is caused by the absence of muscle
dystrophin, the same protein is present but reduced in size or
quantity in BMD. This led to the conclusion that there was a
correlation between the amount of muscle dystrophin and the
severity of the phenotype. Based on this conclusion, most
therapeutic trials for DMD, such as cell or gene therapy [17],
exon skipping [18,19] or the read through approach [PTC
therapeutics [20]] aimed to increase dystrophin expression in an
attempt to ameliorate the course of the disease. However, the
quantity of dystrophin required to rescue the DMD phenotype
and establish a functional muscle has been an unresolved
question.
As in humans, dystrophin deficient muscular dystrophy is
the most common form of muscular dystrophy in dogs [21] and
mutations in the dystrophin gene have been identified for
several breeds. In addition to the Golden Retriever [5,6],
dystrophin mutations have been identified for the Rottweiler
[22], German Short-haired Pointer [23], Cavalier King Charles
Spaniel [24], Welsh Corgi [25] and Labrador Retriever [4]. The
GRMD mutation was also passed to the Beagle breed by mating
with GRMD dogs [26]. In contrast to mdx mice, which are
almost asymptomatic despite the absence of muscle dystrophin,
most dystrophin deficient dogs show a severe phenotype that is
comparable to human DMD. Where a large enough number of
dystrophic dogs have been identified of certain breeds, such as
the Golden Retriever and Labrador Retriever, a spectrum of
clinical severity has been identified with most dogs showing a
severe myopathic phenotype, but exceptions can be noted with
milder phenotypes [6,27].
One exceptional dog, Ringo, was identified in the colony of
Brazilian dystrophic dogs. Ringo and one of his descendants,
Suflair, had a mild clinical course despite no muscle dystrophin.
This observation led us to an investigation of a protective
mechanism that could explain this mild phenotype and suggest
a new therapeutic approach for DMD.
Here we report that LRMD dogs, without muscle dystrophin,
may also be asymptomatic. Evidence that a muscle disease was
present was only indicated on pre-surgical screening of
bloodwork that showed a markedly and persistently elevated
CK activity. Clinical examinations at this early time-point did
not indicate a myopathic phenotype. The diagnosis of a
dystrophic pathologic phenotype was made by biopsy at the
time of neuter. In the following 4 years after the original
diagnosis, clinical signs of mild muscle weakness did develop
and included reluctance or inability to jump into a car or stand
on the pelvic limbs. In this family of dogs with LRMD, the mild
clinical phenotype and absence of dystrophin has been
transmitted in at least 3 generations.
An interesting finding in both the mild and severely affected
Labrador Retrievers in our study was the absence of the
7
previously reported insertion between exons 19 and 20 [4] in
the dystrophin gene in LRMD (Fig. 6C). As in humans with
dystrophin deficiency, this finding suggests that more than one
mutation in dystrophin affects the Labrador Retriever breed.
A striking finding was robust regeneration in the muscles of
all dystrophin deficient asymptomatic Labradors at the time of
muscle biopsy (Fig. 2B). A direct comparison of regeneration in
muscle biopsy specimens of minimally affected Labrador
Retrievers with that of severely affected LRMD dogs with
dystrophin deficiency was not possible as different muscles
were evaluated and at different time points. Expression of
utrophin in regenerating fibers in CXLMD in Golden Retrievers
has been previously described [28]. Here, utrophin expression
in both the mild and severely affected Labrador Retrievers was
limited to regenerating fibers and not expressed on control dog
muscle (Fig. 4). A comparable finding was observed in the
Brazilian dogs, where utrophin expression in the mildly
affected Ringo and Suflair did not differ from severely affected
GRMD dogs [6].
Our observations in this Labrador Retriever family, the
exceptional dogs from the Brazil GRMD colony [6] and rare
DMD patients [11] confirm a paradigm-shift that large
muscles can be partially functional without dystrophin.
Interestingly, although immunostaining and western blot
analysis confirmed the absence of muscle dystrophin in the
LRMD dogs, we did not find any detectable deletion,
duplication or small rearrangement in the dystrophin gene.
Even though a specific mutation has not yet been identified,
our findings lend further support to the hypothesis that, in
exceptional situations, muscle with no dystrophin may be
functional independently of the specific mutation or haplotype.
Sequence analysis of the entire dystrophin cDNA and
promotor is currently underway to search for point mutations
or variants in the promoter region.
In other recent investigations from our group [[29], Pelatti
et al. 2014 unpublished] we found that human mesenchymal
stem cells injected into GRMD dog muscles improved their
clinical phenotype and resulted in an increased lifespan, despite
the fact that in most experiments no dystrophin expression was
found in the injected muscles. This finding also demonstrates
that other factors may have a therapeutic effect protecting
muscles without dystrophin. In short, the observation that a
large animal such as the Golden Retriever or Labrador Retriever
dogs without muscle dystrophin may be almost asymptomatic
opens new avenues for research. Finding the secrets that protect
these dogs is a great challenge which may have important
implications for future treatment.
4.1. Conclusions
Our observations in this Labrador Retriever family, the
exceptional dogs from the Brazil GRMD colony [6] and rare
DMD patients [11] confirm a paradigm-shift that large muscles
can be partially functional without dystrophin. Searching for
modifying factors that protect these dogs and patients from the
deleterious effects of dystrophin deficiency opens new avenues
for research and may have important implications for treating
this devastating condition.
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Authors’ contributions
NMV performed all molecular studies, western blotting and
evaluated affected dogs. LTG conducted the pathological and
immunohistochemical studies and GDS interpreted the results
and determined the clinicopathological diagnosis. EE
performed the pedigree analysis. GDS, LMK, MZ, LMK and
GDS interpreted the data and drafted the manuscript. All
authors read and approved the final manuscript.
Acknowledgements
The authors wish to thank the breeders and owners of the
affected dogs for bringing them for care and attention and for
providing information on their pedigrees. The authors also wish
to thank Drs. Alan Sisson, Sonnya Denis, Stephanie Kube,
Nancy Hatfield, Philip March, Kendra Mikoloski, Julie Pera and
Gena Silver for providing clinical information on affected
Labrador retrievers, Professor Eva Engvall for reading the
manuscript and providing helpful comments, and the funding
agencies FAPESP/CEPID (13/08028-1), CNPQ (303393/20149), INCT (573633/2008-8), ABDIM/AACD and the Duchenne
Research Fund for support.
Abbreviations
CK
GRMD
LRMD
SDS-PAGE
TBST
creatine kinase
Golden retriever muscular dystrophy
Labrador retriever muscular dystrophy
sodium dodecyl sulfate-polyacrylamide
gel electrophoresis
Tris-buffered saline Tween
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