among the entities that cause dilated cardiomyopathy in children are dystrophinopathies , including duchenne muscular dystrophy ( dmd ) , becker muscular dystrophy ( bmd ) , and x - linked dilated cardiomyopathy , allelic conditions caused by defects in dystrophin ( 1 ) .
dystrophin is an important cytoskeletal protein encoded by the dmd gene located at xp21.2 ( 2 ) .
dmd is caused by complete loss of the dystrophin protein complicated by progressive skeletal muscle dystrophic pathology , whereas bmd often results from expression of an altered dystrophin protein leading to milder and a more variable clinical presentation than dmd ( 3 ) .
approximately 70% of bmd patients develop dilated cardiomyopathy ( dcm ) mostly in the third decade of life or later ( 4 , 5 ) ; they rarely develop severe dcm in childhood ( 6 ) . conserving the reading frame of the protein
mutations in which the reading frame is conserved resulting in a functional amino- and carboxy - terminus with little effect on the central rod domain yield a milder phenotype consistent with bmd ( 7 ) , whereas mutations that disrupt the reading frame cause a more severe phenotype consistent with dmd .
the reading frame rule was found to be 9192% consistent in predicting phenotype in simplex cases of young boys ( 8) .
however , more recent studies have shown that this rule tends to be better at predicting phenotype for dmd , and there are more exceptions to this rule in bmd ( 9 , 10 ) .
genotype - phenotype correlations for specific mutations in dystrophin related to predisposition to or protection against dcm have been proposed ( 6 , 11 ) , but exactly how this leads to dcm is poorly understood . here , we present a family in which two siblings and their nephew are affected by similar skeletal muscle abnormalities consistent with bmd .
they have a novel frameshift mutation in the dmd gene responsible for this unique clinical phenotype of bmd and severe early - onset dcm .
the importance of genetic screening of the male family members for early detection of lethal congestive heart failure ( chf ) will be discussed .
there are three affected males in this family spanning two generations ( figure 1a ) .
the first affected member of the family was diagnosed with bmd at 6 years due to mild skeletal muscle weakness ( ii-3 ) .
dystrophin immunostaining in a muscle biopsy was consistent with bmd , and the dystrophin level was quantified as 310% of normal by western blot ( athena diagnostics , worcester , ma ) .
he was diagnosed with attention deficit hyperactivity disorder ( adhd ) , but otherwise remained relatively symptom - free for a long time . at 12 years , however , he developed persistent cough resistant to conventional bronchodilator treatment .
initial echocardiogram revealed dilated lv with severely diminished lv systolic function ( left ventricle shortening fraction of less than 10% ) .
his clinical status continued to deteriorate despite maximum anti - congestive medications , and he was admitted for further management of intractable chf .
hemodynamic assessment by cardiac catheterization showed severe lv dysfunction : lv end - diastolic pressure ( lvedp ) 35 mmhg and cardiac index ( ci ) 1.8 l / min / m under mechanical ventilation and continuous intravenous inotrope infusion .
he died at age 14 due to a cerebral thromboembolic event despite maximum medical treatment while awaiting a heart transplant .
his younger brother ( ii-4 ; 14 years ) was diagnosed as bmd at 3 years of age with mild muscle weakness and failure to thrive .
he has cognitive impairment with function in the range of 68 years old ( at 14 years old ) and a seizure disorder of unknown etiology .
his cardiac status has been followed closely since 6 years of age because of his brother s history of early - onset of progressive dcm .
sequencing ( emory genetics laboratory , decatur , ga ) revealed a novel frameshift mutation in exon 27 of the dmd gene ( c.3779_3785delctttggainsgg ) in which 7 base pairs are deleted and two are inserted ( figure 1b ) .
this predicts an amino acid substitution and premature termination in the novel reading frame 8 codons downstream ( p.thr1260argfs*8 ) .
no other potential disease - causing variants were found in the gene . despite this predicted truncation of protein translation , immunofluorescence studies of a quadriceps muscle biopsy at age 14 instead showed reduced staining for dystrophin and other proteins of the dystrophin - glycoprotein complex and upregulation of utrophin consistent with bmd ( figure 2 ) .
the greatest reduction in dystrophin immunofluorescence ( perhaps absence of staining ) was with an antibody that detects an epitope encoded by exons 27 - 28 ( figure 2f ) .
dystrophin epitopes on either side of exons 27 - 28 were present ( figure 2c , d , e , and g ) .
dystrophin was also detected in western blots from the same muscle biopsy using a carboxy terminus antibody .
the total amount of the patient s dystrophin was greatly reduced , and the molecular weight appeared to be slightly reduced ( data not shown ) .
he had normal cardiac function through age 11 years , after which progressive lv systolic dysfunction and dilatation were noted by echocardiogram .
his symptoms of chf continued to worsen over the next 2 years despite escalating medical treatment , and he was admitted to the hospital at 14 years because of severe respiratory distress and cardiac cachexia .
echocardiogram showed markedly dilated lv ( lvidd 7.7 cm : z - score + 9.1 ) with severely diminished lv systolic function ( lvsf 15% ) .
initial hemodynamic assessment by cardiac catheterization was consistent with mild to moderate lv dysfunction under continuous intravenous milrinone infusion ( lvedp 12 mmhg and ci 2.1 l / min / m ) .
his clinical condition deteriorated despite maximum medical treatment including mechanical ventilation , and eventually he underwent implantation of left ventricular assist device ( heartware hvad , framingham , ma ) .
he was discharged home with improved quality of life . the 7 year old nephew ( iii-1 ) of these two affected boys
he failed to thrive despite maximizing nutritional efforts ( < 1 percentile ) and showed generalized muscle weakness and mild developmental delay . at 18 months
he was noted to have serum ck above 13,000 iu / l , and he has been followed regularly since that time with a presumed diagnosis of bmd . molecular analysis revealed identical familial frameshift mutation in dmd to his uncle ( ii-4 ) . at 18 months
he was noted to have serum ck above 13,000 iu / l , and he has been followed regularly since that time with a presumed diagnosis of bmd .
female carriers in the family , the siblings mother ( i-2 ) and their sister ( ii-1 ) , have had no symptoms of muscle weakness or chf .
there is no further family history is available for i-2 , as she was adopted in her early childhood .
we report a family in which two male siblings with bmd developed severe , early - onset , progressive dcm . both siblings developed intractable chf by age 12 that was resistant to conventional anti - congestive medications .
bmd patients are known to have milder skeletal muscle involvement than dmd patients and commonly develop dcm in their third decade or later .
cardiac dysfunction is a more frequent primary cause of death in bmd than in dmd ( 4 , 12 , 13 ) .
there are sporadic case reports of early onset dcm in bmd , but our patients are unique because of their earlier onset , multiple family member involvement with the same clinical phenotype , and a novel genotype .
dystrophinopathy refers to a clinical spectrum of mutation of dmd gene encompassing bmd , dmd , and x - linked dcm .
x - linked dcm can present as a similar clinical course as ours , as reported by others ( 1416 ) .
however , all 3 patients here initially presented with primary skeletal muscle weakness with markedly increased serum ck , which is quite different from x - linked dcm where there should be no or very little skeletal muscle involvement ( 14 , 15 , 17 ) . skeletal muscle biopsy demonstrated that two brothers showed markedly reduced but positive dystrophin protein expression consistent with bmd .
collectively , we believe the affected brothers have bmd with severe early - onset dcm rather than x - linked dcm with coincidental skeletal myopathy . disproportionally severe cardiac phenotype has been reported in limb - girdle type muscular dystrophy with relatively mild skeletal involvement ( 18 ) .
the x - linked dmd gene has 79 coding exons covering 2.6 million base pairs .
the large size of the dmd gene makes it vulnerable to mutation , mostly by deletion of one or more exons .
dmd is caused by genetic mutations that lead to disruption of the reading frame of the dystrophin transcript and premature abortion of dystrophin synthesis ( 19 ) .
bmd mutations usually do not disrupt the translational reading frame , and are typically in conjunction with either exon deletions or point mutations that alter splicing such that the resultant mrna maintains the open reading frame and leads to production of a partially functional but aberrant protein ( 2022 ) .
previous reports described patients with bmd phenotype with nonsense mutations as a result of altered exon splicing and exon skipping , excluding the nonsense mutation containing exon ( 20 , 23 , 24 ) in our bmd patients ( ii-4 and iii-1 ) , we postulate that the mutation in exon 27 ( c.3779_3785delctttggainsgg ) results in altered splicing and mrna that allows production of a truncated dystrophin protein .
this interpretation stems from immunohistochemical analysis of a muscle biopsy that demonstrates expression of exons proximal and distal to exon 27 ( see figure 2 ) .
unfortunately , we were unable to recover mrna of sufficient quality from archived muscle to test this hypothesis directly , but we note that disruption of the splicing enhancer sequence within exon 27 of the dmd gene by nonsense mutation can induce partial exon skipping , and thus results in a bmd phenotype ( 20 , 21 ) .
however , this early - onset of severe progressive dcm in bmd patients , as seen in this family , has not been reported and can not be solely explained by the exon skipping mechanism .
kaspar et al . proposed that the deletions affecting the amino - terminal domain ( exons 2 - 8 ) are associated with the early - onset of dcm ( 6 ) , but it does not appear that our cases follow this rule . double or multiple gene mutations are known to be responsible for more severe clinical phenotype in some hypertrophic cardimyopathy ( hcm ) ( 2527 ) and rarely in dcm ( 28 ) .
the possibility of second mutation in our cases can not be ruled out , as we have not performed sequencing of other single gene causes of dcm or whole - exome sequencing .
genetic predictors of early onset of dcm in bmd patients have been studied extensively ( 6 , 11 ) , but the results are not conclusive as to which genotypes predict a worse natural course
. there may be a fundamental difference in regulation of dmd gene transcription between skeletal and cardiac muscle . in this family ,
all three affected children developed a nonspecific central nervous system abnormality , but the clinical hallmark of the two brothers is early - onset lethal dcm . because early detection of this progressive dcm is essential for optimum management , further effort in investigating genotype - phenotype correlation in bmd should be encouraged .
 we report a family in which two male siblings with becker muscular dystrophy ( bmd ) developed severe dilated cardiomyopathy ( dcm ) and progressive heart failure ( hf ) at age 11 ; one died at age 14 years while awaiting heart transplant and the other underwent left ventricular assist device ( lvad ) implantation at the same age 
 . genetic analysis of one sibling showed a novel frameshift mutation in exon 27 of duchenne muscular dystrophy ( dmd ) gene ( c.3779_3785delctttggains gg ) , in which 7 base pairs are deleted and two are inserted . while this predicts an amino acid substitution and premature termination ( p.thr1260argfs*8 ) , muscle biopsy dystrophin immunostaining instead indicates that the mutation is more likely to alter splicing . 
 despite relatively preserved skeletal muscular performance , both siblings developed progressive heart failure secondary to early onset dcm . 
 in addition , their 7 year old nephew with delayed gross motor development , mild proximal muscle weakness , and markedly elevated serum creatine kinase ( ck ) level ( > 13,000 
 iu / l ) at 16 months was recently demonstrated to have the familial dmd mutation . 
 here we report a novel genotype of bmd with early onset dcm and progressive lethal heart failure during early adolescence . 