Dilated cardiomyopathy (DCM) is a primary heart
muscle disease characterized by left ventricular dilation
and systolic dysfunction, with secondary diastolic dys-
function and occasionally associated right ventricular
disease (1). This disorder has an incidence of
3.5–8.5/100,000 population per year and a prevalence
of approximately 36/100,000 population (2, 3), which
appears to be on the rise. In addition, DCM is the most
common reason for heart failure and for cardiac trans-
plantation in the US, with an estimated cost of $10 bil-
lion to $40 billion yearly (4).
The underlying causes of DCM are heterogeneous (5,
6), including myocarditis, drug toxicity (adriamycin),
and ischemia-induced, metabolic, mitochondrial, and
genetic abnormalities. A genetic cause of DCM is identi-
fied in approximately 30% of cases (7–9), with autosomal
dominant inheritance being the most common (6). X-
linked, autosomal recessive, and mitochondrial inheri-
tance have also been reported, albeit less frequently (10).
In the past several years, the genetic basis of DCM has
been sought, resulting in the identification of multiple
genetic loci and five genes causing DCM to date. For X-
linked DCM, two genes have been identified, including
tafazzin (G4.5)in cases of the infantile-onset DCM (Barth
syndrome) (11, 12) and isolated left ventricular non-
compaction (13, 14), and dystrophin in later-onset X-
linked cardiomyopathy (XLCM) (15–17). In the more
common autosomal dominant DCM, five loci have been
mapped for pure DCM (1q32 [ref. 18], 2q31 [ref. 19],
9q13-q22 [ref. 20], 10q21-q23 [ref. 21], and 15q14 [ref.
22]), and four loci have been mapped in families with
DCM and associated with conduction disease (1p1-1q21
[ref. 23], 2q14-q22 [ref. 24], 2q35 [ref. 25], 3p25-p22 [ref.
26], and 6q23 [ref. 27]). Thus far, only the gene on chro-
mosome 15q14 encoding cardiac actin (22), the gene on
chromosome 2q35 encoding desmin (25), and the gene
on chromosome 1p1-1q21 encoding laminA/C(28) have
been identified and mutations characterized.
We have proposed a “final common pathway”
hypothesis (29, 30), which states that hereditary car-
diovascular diseases with similar phenotypes and
genetic heterogeneity will occur due to abnormalities
in genes encoding proteins of similar function or genes
encoding proteins participating in a common pathway
cascade. In the case of DCM, we have proposed that
mutations affect elements of the cell cytoarchitecture,
based around the cytoskeleton (i.e., a cytoskeletalopa-
thy) and sarcolemma, but also including elements that
interact with the cytoskeleton including dystrophin,
The Journal of Clinical Investigation|September 2000| Volume 106| Number 5
Mutations in the human δ-sarcoglycan gene in familial
and sporadic dilated cardiomyopathy
Shinichi Tsubata,1,2Karla R. Bowles,3Matteo Vatta,2Carmelann Zintz,2Jack Titus,4
Linda Muhonen,5Neil E. Bowles,2and Jeffrey A. Towbin2,3,6
1Department of Pediatrics, Toyama Medical and Pharmaceutical University, Toyama, Japan
2Department of Pediatrics, Section of Cardiology, and
3Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA
4The Jesse Edwards Cardiac Registry, Minneapolis, Minnesota, USA
5Department of Pediatrics, Section of Cardiology, Orange County Children’s Hospital, Orange, California, USA
6Department of Cardiovascular Sciences, Baylor College of Medicine, Houston, Texas, USA
Address correspondence to: Jeffrey A. Towbin, Department of Pediatrics, Section of Cardiology, Baylor College of Medicine,
One Baylor Plaza, Room 333E, Houston, Texas 77030, USA.
Phone: (713) 798-7342; Fax: (713) 798-8085; E-mail: email@example.com.
Received for publication December 21, 1999, and accepted in revised form July 25, 2000.
Dilated cardiomyopathy (DCM) is a major cause of morbidity and mortality. Two genes have been
identified for the X-linked forms (dystrophin andtafazzin), whereas three other genes (actin, lamin A/C,
and desmin) cause autosomal dominant DCM; seven other loci for autosomal dominant DCM have
been mapped but the genes have not been identified. Hypothesizing that DCM is a disease of the
cytoskeleton and sarcolemma, we have focused on candidate genes whose products are found in these
structures. Here we report the screening of the human δ-sarcoglycangene, a member of the dystrophin-
associated protein complex, by single-stranded DNA conformation polymorphism analysis and by
DNA sequencing in patients with DCM. Mutations affecting the secondary structure were identified
in one family and two sporadic cases, whereas immunofluorescence analysis of myocardium from
one of these patients demonstrated significant reduction in δ-sarcoglycanstaining. No skeletal mus-
cle disease occurred in any of these patients. These data suggest that δ-sarcoglycanis a disease-causing
gene responsible for familial and idiopathic DCM and lend support to our “final common pathway”
hypothesis that DCM is a cytoskeletalopathy.
J. Clin. Invest. 106:655–662 (2000).
the dystrophin-associated glycoprotein complex (DAG;
i.e., the sarcoglycans and dystroglycans), and interme-
diate filaments. Other final common pathways for spe-
cific cardiac phenotypes include the sarcomere in
hypertrophic cardiomyopathy (31) and ion channels in
cardiac rhythm disorders, such as long QT syndromes
and Brugada syndrome (32).
Animal models of cardiomyopathy have also been
described, including the BIO14.6 hypertrophic car-
diomyopathy and the TO-2 DCM hamsters (33, 34),
which are both due to mutations in the δ-sarcoglycan
gene (35–37). These animals also exhibit histological
features of muscular dystrophy (38). Mutations in
this gene in humans cause autosomal recessive limb-
girdle muscular dystrophy, LGMD2F (39), a disorder
in which skeletal muscle disease can vary from mild
(i.e., ambulatory beyond 15 years, similar to Becker
muscular dystrophy [BMD]) to severe (i.e., similar to
Duchenne muscular dystrophy [DMD] with early
requirement of a wheelchair), and cardiac involve-
ment has been documented in some patients (40). In
addition, other LGMD2 disorders (LGMD2C, 2D, 2E)
are caused by sarcoglycan mutations (γ-, α-, and β-
sarcoglycan, respectively), suggesting that some
LGMD phenotypes are sarcoglycanopathies. LGMDs
may also include cardiac involvement associated with
skeletal myopathy (41).
For these reasons, we have begun to analyze
patients with DCM for mutations in genes encoding
these proteins. In this report, we describe the identi-
fication of mutations in the δ-sarcoglycan gene in
familial and sporadic cases of pure DCM. This
extends the spectrum of phenotypes seen with sarco-
glycanopathies, now adding pure DCM to the poten-
tial clinical presentation.
Patient evaluation. All patients were evaluated by physi-
cal examination (particularly focused in the cardiac
and neuromuscular systems), chest radiography, elec-
trocardiography, and echocardiography. The left ven-
tricular size and function was evaluated off M-mode
and two-dimensional echocardiographic images as
described previously (17–19). Cardiac catheterization,
angiography and endomyocardial biopsy was per-
formed in some patients based on clinical indication.
After informed consent, blood for lymphoblastoid cell
line immortalization and DNA extraction was
obtained, as described previously (17, 18, 21).
Control individuals. Two hundred unrelated and unaf-
fected individuals (100 male, 100 female), as deter-
mined by history, physical examination, and echocar-
diography, were analyzed. After written informed
consent, blood for lymphoblastoid cell line immortal-
ization and DNA extraction was obtained.
Isolation and characterization of δ-Sarcoglycan genomic
clones. A human BAC DNA PCR pool library (Research
Genetics, Huntsville, Alabama, USA) was screened by
PCR using primers designed to amplify each of the
exons containing the coding region. PCR was per-
formed in a 10-µL reaction containing 1.5 mM MgCl2,
10 pmol of each primer, 0.5 U Taq DNA polymerase
(Life Technologies Inc., Rockville, Maryland, USA),
using a Stratagene Robocyler (La Jolla, California,
USA). After a 5-minute denaturation step at 94°C, 35
rounds of amplification (94°C for 30 seconds,
54–60°C for 30 seconds, and 72°C for 20 seconds)
were performed. This was followed by a 72°C incuba-
tion for 2 minutes.
The exons of δ-sarcoglycan were subcloned into the
vector pZero (Invitrogen, Carlsbad, California, USA).
Clones were identified by whole cell PCR (20 µL reac-
tion) and sequenced using an ABI373 (Perkin-Elmer
Applied Biosystems, Foster City, California, USA) and
Big Dye Terminator chemistry, according to the man-
Single-strand conformational polymorphism analysis.
Mutation analysis was performed using a modifica-
tion of the method of Orita et al. (42). PCR primers
were designed to amplify across the entire human δ-
sarcoglycan gene in an exon-by-exon manner using the
primers in Table 1. Radioactive PCR was performed
with 100 ng genomic DNA in a 10 µL reaction con-
taining 1.5 mM MgCl2, 10 pmol of each primer, 0.05
µCi [α-32P] dCTP (Amersham Life Sciences Inc.,
Arlington Heights, Illinois, USA), 0.5 U TaqDNA poly-
merase, and 30 rounds of amplification (92°C for 30
seconds, Y°C for 30 seconds, 72°C for 30 seconds),
where Y represents the annealing temperature shown
in Table 1. After PCR amplification, the samples were
denatured and then electrophoresed for 24 hours in a
denaturing 10% polyacrylamide:bisacrylamide (50:1;
Bio-Rad Laboratories Inc., Hercules, California, USA)
gel with and without 12% glycerol, at 8 W in a 4°C cold
room. Bands were visualized by exposure of the dried
gels to Kodak BioMax MS-1 film (Eastman Kodak Co.,
Rochester, New York, USA).
DNA sequencing and protein structural analysis. Normal
and aberrant single-strand conformational polymor-
phism (SSCP) conformers were cut directly from dried
gels, eluted in 100 µL of distilled water (65°C for 30
minutes), and then reamplified. After purification
using Qiaquick columns (QIAGEN Inc., Valencia, Cal-
ifornia, USA), PCR products were sequenced, as
already described here. Protein secondary structure
predictions were performed using the Garnier-
Osguthorpe-Robson algorithm (43) with the Wiscon-
sin Package (version 10.0), Genetics Computer Group
(Madison, Wisconsin, USA).
Immunohistochemistry. Frozen myocardial sections (5-
µm) were cut from the left and right ventricles. Unfixed
sections were stained, using anti–α-, anti–β-, anti–γ-,
and anti–δ-sarcoglycan antibodies, as well as antidys-
trophin (COOH-terminal antibody; Novocastra, New-
castle, United Kingdom). Each primary antibody was
diluted 1:10 in PBS (pH 7.2) containing 5% BSA and
then added to the sections; these were incubated for 30
minutes at room temperature. The slides were washed
The Journal of Clinical Investigation|September 2000|Volume 106|Number 5
three times in 0.1X PBS (pH 7.2) at room temperature.
The sections were then incubated with secondary anti-
body (FITC-conjugated anti-mouse; Novocastra), dilut-
ed 1:400 in PBS (pH 7.2) containing 5% BSA, for 15 min-
utes at room temperature. The slides were washed three
times in 0.1X PBS (pH 7.2) and mounted with Cytoseal
280 mounting medium (Stephens Scientific, Riverdale,
New Jersey, USA) before observation.
Phenotypic analysis: familial DCM. One family with famil-
ial DCM (FDCM no. 1100) was identified by history,
physical examination, and echocardiography. All
affected individuals were symptomatic with evidence
of congestive heart failure at young age (Table 2). Neu-
romuscular examination was normal in all individu-
als, including muscle bulk and strength, reflexes, and
gait. All affected individuals remained athletic until
their onset of heart failure or sudden death. Echocar-
diographically, all affected individuals had severely
dilated left ventricular chambers (with Z scores > 4)
and moderate to severe systolic dysfunction (ejection
fractions < 35%). None of the clinically unaffected
members of the family had abnormal echocardio-
grams. Cardiac transplantation was necessary in the
21-year-old son (III:7) of the proband (II:5) as seen in
the pedigree (Figure 1). Before transplant, cardiac
catheterization with angiography was performed. The
coronary arteries were normal on selective angiogra-
phy. Gross and histopathologic examination of the
explanted heart demonstrated features of classic
DCM, including increased heart weight, left ventricu-
lar dilatation, histopathologic evidence of myocyte
hypertrophy, and moderate fibrosis. No evidence of
ischemia was noted, and no inclusions were seen. The
coronary arteries were normal by inspection and his-
tologically. Creatine kinase (CK) was mildly elevated in
this patient (Table 2), with the muscle isoform (CK-
MM) entirely responsible for the elevation. No other
affected members of the family had CK levels analyzed
before death, and the unaffected members (II:2, II:3,
III:3, III:4, and III:5) had normal levels. Autopsy speci-
mens for deceased individuals were pathologically sim-
ilar to those found in the explant of patient III:7, and
the coronary arteries were normal in all cases.
Phenotypic analysis: sporadic DCM. Fifty patients rang-
ing in age from 3 days to 18 years (mean, 9.5 years) with
clinically apparent DCM presenting with heart failure
and echocardiograms diagnostic for DCM were identi-
fied. Cardiac catheterization, angiography and
endomyocardial biopsy was performed in 17 patients,
and inflammatory infiltrate consistent with borderline
(n =4) or active (n =2) myocarditis using the Dallas cri-
teria was found in 35% of these individuals. The
remaining patients were negative for inflammatory
infiltrates. Coronary angiography was normal in all
cases. In eight patients, cardiac transplantation was
performed, whereas five patients died prematurely and
without transplantation. Coronary arteries were nor-
mal in all cases. CK levels were also normal in these
individuals (Table 2).
Molecular analysis: genomic sequences. The cDNA
sequence published by Nigro et al. (44) (GenBank
accession no. X95191) and by Jung et al. (45). (Gen-
Bank accession no. U58331) identified alternative
sequences at the 3′ end of the mRNA in expressed
sequence tags (ESTs) identified in muscle (44) or in pla-
centa (45). Subsequently, we refer to these spliced
forms as the muscle (M) and placental (P) isoforms,
respectively, although both are expressed in the heart
(data not shown).
Screening of a human BAC library identified five
BACs encoding the exons of δ-sarcoglycan. BACs 523E7
and 417E23 encoded exons 2 and 3; BACs 555B9 and
557H6 encoded exons 4, 5, 6, and 7; and BAC 212M24
encoded exons 8 and 9. Subcloning of these BACs into
plasmid vectors, followed by DNA sequence analysis,
produced the sequences of the exon-intron bound-
aries, and primers complementary to intron sequences
were synthesized for SSCP analysis (Table 1). Primers
were designed to amplify across each of the exons
including exon 9 of both the muscle isoform (D-
Sarc9mF and D-Sarc9mR; Table 1) (44) and the pla-
cental isoform (D-Sarc9pF and D-Sarc9pR: Table 1)
(45). Nigro et al. (44) reported the locations of seven
introns within the coding region of human δ-sarcogly-
can mRNA. We identified an eighth intron located
within the 5′ UTR. The location of this intron within
the 5′ UTR suggests that the initiation codon is locat-
ed within exon 2, as occurs in the hamster.
Molecular analysis: SSCP
Familial DCM. SSCP was performed using the primers
designed to amplify across the δ-sarcoglycangene. In fam-
ily FDCM no. 1100, three affected individuals were iden-
The Journal of Clinical Investigation| September 2000|Volume 106| Number 5
Familial DCM pedigree. Pedigree of family FDCM no. 1100. Note the
severity of disease with early-onset CHF and sudden deaths in affect-
ed individuals. SCD, sudden cardiac death; CHF, congestive heart
failure; yo, year old. Filled circles and squares represent affected
females and males, respectively; open circles and squares represent
unaffected females and males, respectively; diagonal line indicates
death; and the arrow is the index case.
tified with abnormal SSCP conformers (Figure 2). None
of the unaffected members of the family and none of the
200 control individuals had this abnormal conformer.
DNA sequence analysis identified a single nucleotide
change, 451T→G in exon 6, which changes the amino
acid at codon 151 from serine to alanine (S151A). This
change from a polar to nonpolar amino acid is signifi-
cant and is predicted to alter the secondary structure of
δ-sarcoglycan, enabling an extended α-helix. Computer
modeling of this portion of the protein (43) supports
secondary structural changes (data not shown) as well,
but functional studies are required to confirm the effect
of these mutations.
Sporadic DCM. SSCP analysis of the fifty sporadic
cases of DCM identified four patients with abnormal
conformers. In two patients, a 3-bp deletion (either
710–712delAGA or 711–713delGAA) of δ-sarcoglycan
exon 9p was identified (Figure 3) that deletes a codon
encoding the amino acid lysine at position 238
(∆K238); screening 200 control individuals, as well as
the phenotypically normal parents of these children,
did not identify the same abnormality. The deletion of
lysine 238 is predicted to result in a change in the sec-
ondary structure in which the folding of the protein is
disrupted, consistent with a disease-causing mutation.
In addition, two other patients had abnormal con-
formers that, upon sequencing, appear to be polymor-
phisms. In one case, a 290G→A transition in exon 4,
which changes the arginine at codon 97 to glutamine
(R97Q), was identified. This 290G→A transition was
previously reported to be a polymorphism (45). In
another patient, a T→A transversion within intron 4,
38 nucleotides from the intron 4–exon 5 boundary, was
found. One of 200 controls was identified with the
identical change, most likely representing a polymor-
phism, especially considering the distance from the
intron-exon boundary. However, in an attempt to doc-
ument whether this caused a change in the splicing of
the mRNA, RNA was isolated from lymphoblastoid cell
lines (from the patient and from a control) and sub-
jected to RT-PCR using primers designed to amplify
this region. However, amplification was unsuccessful,
probably due to limited illegitimate transcription of δ-
sarcoglycan in lymphoblasts.
Immunohistochemistry. Tissue from the explanted heart
of one of the patients with the ∆K238 deletion was avail-
able for immunohistochemical analysis. Frozen sections
of right and left ventricle were stained with antibodies
against α-, β-, γ-, and δ-sarcoglycan, or the COOH-ter-
minus of dystrophin. In parallel, myocardial sections
from the explanted heart of a patient with congenital
heart disease (i.e., control patient) were stained for com-
parison. Although the staining of dystrophin and α-, β-
(data not shown), and γ-sarcoglycan (Figure 4) was
indistinguishable between the control and affected
patient samples, the staining for δ-sarcoglycan was sig-
nificantly reduced in the patient with the ∆K238 muta-
tion (Figure 4). Interestingly the δ-sarcoglycan antibody
is NH2-terminal specific whereas the mutation is
COOH-terminal, suggesting this mutation leads to a
significant change in δ-sarcoglycan structure.
Although the pathophysiology of DCM is well known
(5), the underlying genetic mechanism for this disorder
has remained unclear. Whether the disease results from
The Journal of Clinical Investigation| September 2000|Volume 106| Number 5
Oligonucleotide primers used for SSCP analysis of the human δ-sarco-
Exon Primer Primer sequence
TA(°C) PCR product
TAis the annealing temperature used in the PCR reactions. 9m is exon 9 of the iso-
form identified by Nigro et al. (36) by sequencing an EST of muscle origin, where-
as 9p is exon 9 of the isoform sequenced by Jung et al. (45) from a placental EST.
Mutation analysis of δ-sarcoglycan in familial DCM. (a) SSCP per-
formed using primers for exon 6 of δ-sarcoglycan identifies an abnor-
mal conformer in affected individuals only (arrow). (b) Sequence
analysis demonstrates a T→G substitution at position 151, which
changes the wild-type serine to alanine (S151A).
inflammation, autoimmune, or genetic causes has been
speculated upon for decades (46) but a unifying mech-
anism has not been proved. During the past several
years, however, a variety of clues to the underlying cause
of DCM, as well as the underlying basis for other inher-
ited cardiovascular diseases, have emerged. This has led
us to speculate on the existence of a final common
pathway of cardiovascular disease in which specific
phenotypes result from mutations in families of pro-
teins essential for specific functions. For instance, the
basis for hypertrophic cardiomyopathy (HCM), a pri-
mary heart muscle disease in which ventricular wall
thickening (hypertrophy) and diastolic dysfunction
occur, has been demonstrated to be due to mutations
in genes encoding sarcomeric proteins such as β-
myosin heavy chain, α-tropomyosin, cardiac troponin
T, cardiac troponin I, myosin binding protein-C, essen-
tial and regulatory myosin light chains(reviewed in ref.
31), and cardiac actin (47). In addition, the inherited
long QT syndromes (LQTS) have been shown to be due
to mutations in genes encoding ion channels, such as
the potassium channel genes KVLQT1, KCNE1, and
HERG, KCNE2, and the cardiac sodium channel gene
SCN5A (reviewed in ref. 32). Owing to the consistent
protein classes found to be mutated in phenotypically
similar patients (i.e., the final common pathways of sar-
comeric proteins in HCM; ion channels in LQTS), we
used this final common pathway hypothesis (29, 30,
48) to speculate that similar protein types would be
mutated in DCM as well.
Five genes have been previously identified and char-
acterized in cases of familial DCM. In Barth syn-
drome, the gene G4.5, which encodes a novel protein
family called tafazzins, is mutated (11–14). Although
well characterized at the molecular level, to our
knowledge the function of the encoded protein is not
currently known. However, the gene responsible for
XLCM, dystrophin, is well defined (15–17). This gene,
which also causes Duchenne (DMD) and Becker
(BMD) muscular dystrophy when mutated (49),
encodes a large (427-kDa) cytoskeletal protein that
resides at the inner face of the sarcolemma, colocaliz-
ing with β-spectrin and vinculin. Dystrophin protein
is thought to assume a rod-shaped
structure with an actin-binding domain
at the NH2-terminus. The COOH-ter-
minal domain is associated with a large
transmembrane glycoprotein complex,
the DAG, which is thought to mechan-
ically stabilize the plasma membrane of
muscle cells as well as serving a cell sig-
naling role. This complex is formed by
the dystroglycan subcomplex (α-dys-
troglycan and β-dystroglycan), sarco-
glycan subcomplex (α-, β-, γ-, and δ-
sarcoglycan), caveolin-3, syntrophin,
dystrobrevin, and sarcospan and serves
as a link between cytoplasmic actin, the
membrane, and the extracellular matrix
of muscle via laminin-α2 (50, 51). Mutations in dys-
trophin, the DAG subcomplexes, or laminin result in a
wide spectrum of skeletal myopathy and/or car-
diomyopathy in humans and animal models such as
the mouse or hamster (30–36, 52).
The third mutant gene thus far identified, cardiac
actin, has been identified as the gene responsible for the
chromosome 15q14-linked autosomal dominant
FDCM (22). This gene encodes a member of the thin fil-
ament of the sarcomeric unit. When mutated near the
dystrophin-binding site, DCM occurs. However, when
mutations near the sarcomeric end of actin occur, a
The Journal of Clinical Investigation| September 2000|Volume 106| Number 5
Mutation analysis of δ-sarcoglycan in sporadic DCM. (a and b) Abnor-
mal SSCP conformers in two individuals with sporadic DCM. (c)
Sequence analysis identifies a 3-bp deletion in exon 9p that deletes the
codon for the amino acid lysine at position 238 (∆K238).
Clinical characteristics of patients
FDCM no. 1100
Clinical presentationLVEDD (Z score)EF (Z score)CK (MM%)
CHF, SCD, age 38 y
CHF, SCD, age 14 y
CHF, SCD, age 36 y
CHF, SCD, age 17 y
CHF, transplant, age 21 y
62 mm (5.1)
68 mm (4.0)
70 mm (4.5)
20% (7.1)350 (100%)
CHF, age 9 mo.
CHF, age 14 y
40 mm (8.5)
58 mm (4.8)
CHF, congestive heart failure; SCD, sudden cardiac death; LVEDD, left ventricular end diastolic
dimension; Z score, standard deviation; EF, ejection fraction; CK, creatine kinase; CK (MM%),
creatine kinase muscle isoform percent; ND, not determined.
HCM phenotype develops (46). The likely reason that
this mutant gene causes a DCM phenotype is that the
link between dystrophin and actin is disrupted, thereby
disassociating the actin cytoskeleton from the muscle
membrane and extracellular matrix, leading to cellular
degeneration and necrosis. Recently, mutations in α-
actin were shown to cause the skeletal muscle disorders
actin myopathy and nemaline myopathy as well (53).
The other two genes identified in FDCM are desmin
(2q35) (ref. 25) and lamin A/C(1p1-1q21) (ref. 28), both
of which are thought to cause abnormalities of struc-
tural support when mutated, as well. Interestingly,
these genes have both been shown to be associated with
skeletal myopathy and, in some cases, with conduction
system disease (28, 54, 55). The identification of muta-
tions in δ-sarcoglycan, another member of the cytoskele-
ton/sarcolemmal structural support, further supports
our final common pathway hypothesis (29, 30, 48).
Furthermore, mutations in this gene have previously
been shown to cause either dilated or hypertrophic car-
diomyopathies in the hamster and mouse, providing
support that this gene, which maps to chromosome
5q33-34 in humans (42), is disease-causing in the
patients described in this report.
LGMDs are a group of disorders that are character-
ized by progressive muscle weakness affecting both
upper and lower limbs. They mainly have autosomal
recessive inheritance, elevated CK, and are due to
mutations in sarcoglycans, including LGMD2C (γ-
sarcoglycan), LGMD2D (α-sarcoglycan), LGMD2E (β-
sarcoglycan), and LGMD2F (δ-sarcoglycan). LGMD2F
was initially reported by Nigro et al. (56) in four
Brazilian families, and all affected members had a
frameshift mutation in exon 7 (∆656C) that resulted
in premature truncation of the translatable δ-sarco-
glycan protein. These patients had severe DMD-like
disease. Duggan et al. (57) and Moreira et al. (40) iden-
tified homozygous mutations (W30X and R165X
nonsense mutations, and E262K missense mutation,
respectively) in δ-sarcoglycan in patients with DMD-
like disease as well. In the case of the family studied by
Moreira et al., the electrocardiogram was consistent
with left ventricular hypertrophy, but no other cardiac
information (i.e., echocardiogram) was reported.
Thus, LGMD associated with sarcoglycan mutations
appears to be inherited as a recessive disease. However,
in the patients with DCM described in this report, we
propose that dominant negative mutations in δ-sarco-
glycan result in absent skeletal myopathy in the face of
late-onset DCM. These mutations are similar to those
described in LGMD2F, except that they are heterozy-
gous. Although heterozygotes within LGMD2F fami-
lies have not been described to be affected, it is possible
that cardiac evaluation overlooked cardiac pathology
or the cardiac dysfunction had not become apparent at
the time of evaluation, given that DCM is, in many
instances, age dependent. In DMD and BMD, disorders
of dystrophin, female carriers commonly develop car-
diomyopathy but usually do so later in life than the
affected males. Further, as cardiac disease is now
appearing to be common in most (if not all) skeletal
myopathies, it is not surprising that δ-sarcoglycanmuta-
tions could have wide clinical phenotypic heterogene-
ity. Melacini et al. (41) reported DCM to be relatively
common in sarcoglycanopathies (about 30%), although
they did not find DCM with δ-sarcoglycanmutations in
the LGMD patients with DCM studied.
Interestingly Nigro et al. (44) identified a dominant
missense mutation (N211Y) in δ-sarcoglycan in a fam-
ily with mild proximal myopathy and mild CK eleva-
tions (threefold). Four autosomal dominant forms of
LGMD have also been described (LGMD1A-D). To
our knowledge, only genes for LGMD1B, which is
associated with atrioventricular conduction distur-
bances, and LGMD1C have been identified, namely,
lamin A/C (58) and caveolin-3 (59), respectively. It is
The Journal of Clinical Investigation| September 2000| Volume 106| Number 5
Immunohistochemical analysis of the DAG
complex and dystrophin. The detection of
δ-sarcoglycan (a) and γ-sarcoglycan (b) in
the myocardium of the patient with the
∆K238 mutation of δ-sarcoglycan. Note the
reduction in the intensity of staining of δ-
sarcoglycan, whereas γ-sarcoglycan remains
the same as the control.
possible that mutations in different domains of δ-
sarcoglycan result in either a cardiac or skeletal mus-
cle phenotype, similar to that described for dys-
trophin (15–17, 49). Similarly, these differences could
account for the modes of inheritance (i.e., autosomal
recessive or autosomal dominant).
Multiple animal models with sarcoglycan deficien-
cy have been produced or are naturally occurring,
including the cardiomyopathic hamster due to dele-
tion of exons 1 and 2 of δ-sarcoglycan (35). Hack et al.
(60) generated a γ-sarcoglycan–deficient mouse that
developed progressive muscular dystrophy, pro-
nounced cardiac muscle degeneration, and reduced
survival. These mice also had reduced levels of β- and
δ-sarcoglycan staining of muscle (with normal dys-
trophin, dystroglycan, and laminin-α2) and elevated
CK at baseline (suggesting CK release occurs by mech-
anisms other than mechanical injury) and with exer-
cise. Coral-Vazquez et al. (61) studied mice deficient
in α-sarcoglycan and δ-sarcoglycan and demonstrat-
ed that only δ-sarcoglycan null mice developed car-
diomyopathy, with focal areas of necrosis by 3 months
of age; death occurred by 6 months of age typically.
Coronary artery abnormalities, particularly constric-
tion with pre- and poststenotic dilation and reduction
in lumen size, were noted. This has been supported in
studies in humans (62), but no coronary artery disease
has been found in any of the patients described
here. Coronary angiography and echocardiography
(transthoracic and in some cases transesophageal)
identified normal coronary arteries in all patients
with δ-sarcoglycan mutations, and no evidence of
ischemia was found in the myocardium. Histological-
ly and by gross evaluation, the coronary arteries were
normal in the explanted hearts of the transplanted
sporadic and familial cases. Araishi et al. (63) studied
β-sarcoglycan–deficient mice, which exhibited pro-
gressive muscular dystrophy, muscular hypertrophy,
severe elevations in CK (about 100 times higher than
in wild type), and cardiac fibrosis. Immunohisto-
chemical staining demonstrated α-, β-, γ-, and δ-sarco-
glycan and sarcospan to be absent in the sarcolemma,
whereas laminin-α2, α- and β-dystroglycan, and dys-
trophin were normal. In one patient with a ∆K238
deletion, no reduction in α-, β-, or γ-sarcoglycan or
dystrophin, was noted.
In conclusion, the description of mutations in δ-
sarcoglycan in patients with DCM provides further
support for the concept that the final common path-
way for DCM is the cytoarchitecture, comprising the
cytoskeleton, sarcolemma, and interacting compo-
nents. In addition, the fact that mutations in δ-sarco-
glycan and dystrophin, as well as mutations in G4.5, can
also result in skeletal myopathy, suggests that
patients with DCM should be carefully evaluated for
skeletal muscle weakness and that neurologists caring
for patients with skeletal myopathies should be cog-
nizant of the potential for associated cardiomy-
opathies in their patients.
We thank P. Sen of the Child Health Research Center,
Baylor College of Medicine, for the DNA sequence
analysis. K. Bowles is a Howard Hughes Medical Insti-
tute predoctoral fellow. This work was supported by
the Abercrombie Cardiology Fund of Texas Children’s
Hospital (N.E. Bowles), Texas Children’s Hospital
Foundation Chair in Pediatric Cardiac Research (J.A.
Towbin) and NIH grants from the National Heart,
Lung, and Blood Institute (J.A. Towbin).
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