restrictive cardiomyopathy ( rcm ) is very rare in children and it is characterized by dilated atria , elevated end - ventricular diastolic pressure , and severe diastolic dysfunction resulting from increased stiffness of the myocardium , .
rcm carries a poor prognosis with a low survival rate and ultimately requires heart transplantation. pediatric rcm is most commonly idiopathic and its molecular basis is still unclear .
recently , mutations in the sarcomeric protein genes ( cardiac troponin i , tnni3 ; cardiac troponin t , tnnt2 ; -cardiac actin , actc ; -myosin heavy chain , myh7 ) have been identified in pediatric rcm , which suggests that sarcomeric protein mutations may be important causes of rcm. here , we performed genetic investigations of candidate genes that have been reported in rcm and identified a missense mutation in the tnni3 gene in a 12-year - old girl with rcm .
the patient and her family were recruited at nanjing children 's hospital into an ongoing research protocol approved by the institution 's ethics committee .
all participants gave informed consents and were evaluated by family history , physical examination , electrocardiogram and echocardiogram .
genomic dna was extracted from peripheral blood samples using a puregene dna purification kit ( gentra systems , minneapolis , mn , usa ) according to the manufacturer 's instructions .
genetic analysis was performed for 4 candidate genes ( tnni3 , tnnt2 , actc , myh7 ) known to associate with rcm by bidirectional sequencing of all the coding exons .
the patient and her family were recruited at nanjing children 's hospital into an ongoing research protocol approved by the institution 's ethics committee .
all participants gave informed consents and were evaluated by family history , physical examination , electrocardiogram and echocardiogram .
genomic dna was extracted from peripheral blood samples using a puregene dna purification kit ( gentra systems , minneapolis , mn , usa ) according to the manufacturer 's instructions .
genetic analysis was performed for 4 candidate genes ( tnni3 , tnnt2 , actc , myh7 ) known to associate with rcm by bidirectional sequencing of all the coding exons .
the patient was a 12-year - old chinese girl and experienced her first episode of dyspnea on exertion .
an echocardiogram disclosed that the girl had a structurally normal heart with normal biventricular dimensions , normal biventricular wall thickness and normal systolic functions , but with massive biatrial enlargement ( fig 1 ) , markedly left ventricular ( lv ) diastolic dysfunction , which is consistent with restrictive lv filling pattern : a decreased e - wave deceleration time ( 102 ms , normal > 150 ms ) , an abnormal e / a wave ratio of 2.29 ( normal < 2 ) , and a decreased isovolumic relaxation time ( 30 ms , normal > 70 ms ) .
electrocardiogram ( ecg ) showed sinus rhythm , and biatrial enlargement , and diffuse t - wave changes ( fig 2 ) .
the case had a mild short pr interval , but showed no evidence of neuromuscular diseases and metabolic diseases .
magnetic resonance imaging ( mri ) revealed no delayed gadolinium enhancement and demonstrated enlargement in both atria .
etiologic investigations revealed normal karyotype , normal plasma amino acids and urine organic acids , and normal plasma autoantibody .
the results of the major laboratory tests were within normal range except for a marked elevation in plasma pro - bnp level ( 1023 ng / l ) ( the upper limit of normal range , 115 ng / l ) .
endomyocardial biopsy was not performed in this case due to refusal by the parents . a 2-dimensional echocardiographic image ( apical 4-chamber view ) showing a markedly enlarged la and ra with normal biventricular size .
ecg showing sinus rhythm , incomplete right bundle branch block , st segment depression in the inferior leads , and marked biatrial enlargement .
genetic analysis was performed for 4 candidate genes ( tnni3 , tnnt2 , actc , and myh7 ) known to associate with restrictive cardiomyopathy by bidirectional sequencing of all the coding exons .
a heterozygous 575 g > a mutation in exon 8 of tnni3 was identified in the patient .
the mutation resulted in the substitution of histidine for arginine at amino acid 192 ( r192h ) .
amino acid 192 ( arginine ) is highly conserved across species and this missense mutation has previously been described to be associated with both restrictive and hypertrophic cardiomyopathy , ( fig .
3 ) . this mutation was absent in her parents and 100 healthy subjects screened at our institution .
the patient was a 12-year - old chinese girl and experienced her first episode of dyspnea on exertion .
an echocardiogram disclosed that the girl had a structurally normal heart with normal biventricular dimensions , normal biventricular wall thickness and normal systolic functions , but with massive biatrial enlargement ( fig 1 ) , markedly left ventricular ( lv ) diastolic dysfunction , which is consistent with restrictive lv filling pattern : a decreased e - wave deceleration time ( 102 ms , normal > 150 ms ) , an abnormal e / a wave ratio of 2.29 ( normal < 2 ) , and a decreased isovolumic relaxation time ( 30 ms , normal > 70 ms ) .
electrocardiogram ( ecg ) showed sinus rhythm , and biatrial enlargement , and diffuse t - wave changes ( fig 2 ) .
the case had a mild short pr interval , but showed no evidence of neuromuscular diseases and metabolic diseases .
magnetic resonance imaging ( mri ) revealed no delayed gadolinium enhancement and demonstrated enlargement in both atria .
etiologic investigations revealed normal karyotype , normal plasma amino acids and urine organic acids , and normal plasma autoantibody .
the results of the major laboratory tests were within normal range except for a marked elevation in plasma pro - bnp level ( 1023 ng / l ) ( the upper limit of normal range , 115 ng / l ) .
endomyocardial biopsy was not performed in this case due to refusal by the parents . a 2-dimensional echocardiographic image ( apical 4-chamber view ) showing a markedly enlarged la and ra with normal biventricular size .
ecg showing sinus rhythm , incomplete right bundle branch block , st segment depression in the inferior leads , and marked biatrial enlargement .
genetic analysis was performed for 4 candidate genes ( tnni3 , tnnt2 , actc , and myh7 ) known to associate with restrictive cardiomyopathy by bidirectional sequencing of all the coding exons .
a heterozygous 575 g > a mutation in exon 8 of tnni3 was identified in the patient .
the mutation resulted in the substitution of histidine for arginine at amino acid 192 ( r192h ) .
amino acid 192 ( arginine ) is highly conserved across species and this missense mutation has previously been described to be associated with both restrictive and hypertrophic cardiomyopathy , ( fig .
3 ) . this mutation was absent in her parents and 100 healthy subjects screened at our institution .
over the past decade , molecular genetic analyses have revealed dozens of mutations in sarcomeric protein genes , which encode the contractile unit of cardiac muscles , in both dcm and hcm .
these findings have shown that mutations in specific functional regions of sarcomeric protein genes result in different phenotypes .
an interesting feature of cardiomyopathies is that rcm may overlap with hcm , especially in many familial cases . up to now ,
more than 900 mutations have been confirmed to be associated with hcm . since the first sarcomere gene mutation was identified in the tnni3 gene in rcm in 2003 ,
several heterozygous mutations in tnni3 , tnnt2 , actc , and myh7 have been reported to be associated with rcm , indicating that rcm may also be caused by single heterozygous mutations in the genes encoding sarcomeric proteins . in this report
, we identified a known heterozygous missense mutation in exon 8 of tnni3 ( r192h ) in a 12-year - old chinese girl . according to our knowledge ,
the r192h ctni mutation was firstly reported by mogensen in 2003 in a 19-year - old rcm patient , who died of heart failure .
this mutation was also found in a rcm family with hypertrophic physiology , in which all the three persons affected had a early onset of rcm from the first to third decades .
all those reports suggest that this mutation may have a good genotype - phenotype correlation with early age of disease onset .
rcm and hcm may occur in one family with the same sarcomere gene mutation , which shows phenotypic heterogeneity in cardiomyopathies , .
the r192h mutation is located in the highly conserved c - terminal region in tnni3 and in vitro studies showed that this mutation disrupts interactions within the troponin complex .
found that the r192h mutation increased the ca sensitivity of force development in skinned fibers .
furthermore , du et al . showed that the transgenic r193h mice , similar to human r192h , demonstrated rcm characteristics .
cardiomyocyte contraction is regulated primarily by the interactions between the intracellular calcium concentration and its major senor - the troponin complex .
tnni3 is the inhibitory component of the troponin complex and it can bind to actin - tropomyosin and prevent muscle contraction by inhibition of actin - tropomyosin - activated myosin atpase activity , .
the occurrence of tnni3 mutations in rcm was first reported by mogensen , who found 6 novel mutations located in the conserved and functional important regions of the gene . to date
, at least eight tnni3 mutations including seven substitutions and one deletion were identified in rcm that occupied several critical functional domains : the inhibitory region , the switch region and the c - terminus , , .
studies found that the c - terminus of ctni plays an important role in maintaining the diastolic parameters of the heart .
three of the eight mutations are located in the conserved c - terminal region of tnni3 protein .
tnni3 c - terminus is required for normal inhibitory function and studies using transgenic mice demonstrated that mutations existing in this region had serious consequences for cardiac function . in vitro studies also have revealed rcm - linked tnni3 c - terminus mutations sensitized the myofilaments to ca , slowed relaxation and ca transient decay rate .
however , most identified hcm linked tnni3 mutations clustered within the same functional domains shared by rcm , and the molecular mechanism whereby mutations in the same functional region of tnni3 result in diverse phenotypic expression needs further studies . in summary
, we report a tnni3 missense mutation ( r192h ) in idiopathic rcm in a 12-year - old chinese girl .
this case further improves our knowledge of the causes of cardiomyopathic disease and shows that the spectrum of sarcomeric gene mutations may be involved in pediatric rcm .
 pediatric restrictive cardiomyopathy is rare and most commonly idiopathic in origin . here 
 , we applied a candidate gene approach and identified a missense mutation in the cardiac troponin i gene in a 12-year - old chinese girl with restrictive cardiomyopathy . 
 this study indicates that mutation in sarcomere protein genes may play an important role in idiopathic pediatric restrictive cardiomyopathy . 