Familial hypertrophic cardiomyopathy associated with a novel missense mutation affecting the ATP-binding region of the cardiac beta-myosin heavy chain

Combining whole exome sequencing with in silico analysis and clinical data to identify candidate variants in pediatric left ventricular noncompaction

BACKGROUND

Understanding the overall variant burden in pediatric patients with left ventricular noncompaction (LVNC) has clinical implications. Whole exome sequencing (WES) allows detection of coding variants in both candidate cardiomyopathy genes and those included on commercial panels. Other lines of evidence, including in silico analysis, are necessary to reduce the overwhelming number of variants to those most likely having a phenotypic impact.

METHODS

Five families, including five pediatric probands with LVNC, 5 other affected, and 10 unaffected family members, had WES performed, followed by bioinformatics filtering and Sanger sequencing. Review of the HGMD, variant classification by ACMG guidelines, and clinical information were used to further refine complex genotypes.

RESULTS

One nonsense and eleven missense variants were identified. In Family 1, affected siblings carried digenic heterozygous variants: E1350K-MYH7 and A276V-ANKRD1. The proband also carried heterozygous W143X-NRG1. Four affected members of Family 2 carried K184Q-MYH7 while unaffected members did not. In Family 3, homozygous A161T-MYH7 and heterozygous P4935T-OBSCN variants were identified in the proband with the latter being absent in his unaffected brother. In Family 4, proband's father and half-sibling have mild hypertrabeculation and carry T3796I-PLEC. The proband, carrying T3796I-PLEC and V2878A-OBSCN, demonstrated higher trabeculation burden. The proband in Family 5 carried four variants, R3247W-PLEC, C92Y-ERG, T1233M-NCOR2, and E54K-HIST1H4B. Application of ACMG criteria and clinical data revealed that W143X-NRG1, P4935T-OBSCN, and V2878A-OBSCN likely have no phenotypic role.

CONCLUSIONS

We report nine variants, including novel T3796I-PLEC and biallelic A161T-MYH7, likely contributing to phenotypes ranging from asymptomatic hypertrabeculation to severe LVNC with heart failure.

Motor Proteins and Spermatogenesis

Unlike the intermediate filament- and septin-based cytoskeletons which are apolar structures, the microtubule (MT) and actin cytoskeletons are polarized structures in mammalian cells and tissues including the testis, most notable in Sertoli cells. In the testis, these cytoskeletons that stretch across the epithelium of seminiferous tubules and lay perpendicular to the basement membrane of tunica propria serve as tracks for corresponding motor proteins to support cellular cargo transport. These cargoes include residual bodies, phagosomes, endocytic vesicles and most notably developing spermatocytes and haploid spermatids which lack the ultrastructures of motile cells (e.g., lamellipodia, filopodia). As such, these developing germ cells require the corresponding motor proteins to facilitate their transport across the seminiferous epithelium during the epithelial cycle of spermatogenesis. Due to the polarized natures of these cytoskeletons with distinctive plus (+) and minus (-) end, directional cargo transport can take place based on the use of corresponding actin- or MT-based motor proteins. These include the MT-based minus (-) end directed motor proteins: dyneins, and the plus (+) end directed motor proteins: kinesins, as well as the actin-based motor proteins: myosins, many of which are plus (+) end directed but a few are also minus (-) end directed motor proteins. Recent studies have shown that these motor proteins are essential to support spermatogenesis. In this review, we briefly summarize and evaluate these recent findings so that this information will serve as a helpful guide for future studies and for planning functional experiments to better understand their role mechanistically in supporting spermatogenesis.

Echocardiographic evaluation of pre-diagnostic development in young relatives genetically predisposed to hypertrophic cardiomyopathy

Identification of the first echocardiographic manifestations of hypertrophic cardiomyopathy may be important for clinical management and our understanding of the pathogenesis. We studied the development of pre-diagnostic echocardiographic changes in young relatives to HCM patients during long-term years follow-up. HCM-relatives not fulfilling the diagnostic criteria for HCM and age of <18 years were included in this study. We performed echocardiographic evaluations at inclusion and after 12 ± 1 years follow-up. Based on family screening of 11 sarcomere genes, CRYAB, α-GAL, and titin, we evaluated: (1) non-carriers (known family mutation ruled out-controls), (2) carriers (phenotype negative gene mutation carriers) and (3) phenotype negative relatives with unknown genetic status (relatives from families without identified mutations). At inclusion (age 11 ± 5 years), there were no differences in echocardiographic chamber dimensions, systolic or diastolic function between the three groups. During follow-up (age 23 ± 5 years), carriers (n = 8) developed lower left ventricular end-diastolic dimension (LVEDd) compared to non-carriers (n = 23) (41 ± 4 vs. 46 ± 4 mm; p = 0.04) and a higher ratio of early left ventricular filling velocity and early diastolic velocity of lateral mitral annulus (E/e' 6 ± 1 vs. 5 ± 1; p = 0.003). No significant differences in LVEDd or E/e' were found between relatives with unknown genetic status (n = 24) and non-carriers though Z-scores for these parameters were >2 in a subset of relatives with unknown genetic status. Children carrying pathogenic sarcomere gene mutations develop reduced LVEDd and increased E/e' as first pre-diagnostic echocardiographic manifestations during follow-up into adulthood.

Penetrance of hypertrophic cardiomyopathy in children and adolescents: a 12-year follow-up study of clinical screening and predictive genetic testing

BACKGROUND

The penetrance of hypertrophic cardiomyopathy (HCM) during childhood and adolescence has been only sparsely described. We studied the penetrance of HCM and the short- and long-term outcomes of clinical screening and predictive genetic testing of child relatives of patients with HCM.

METHODS AND RESULTS

Ninety probands and 361 relatives were included in a family screening program for HCM (1994-2001). Eleven sarcomere genes, CRYAB, α-GAL, and titin were screened. Sixty-six relatives and 4 probands were <18 years of age at inclusion. Twelve child relatives were mutation carriers (age, 12 ± 5 years), and 26 had unknown genetic status, ie, relatives from families without identified mutations (n = 21) or not tested (n = 5) (age, 11 ± 5 years). Twenty-eight noncarriers (42%; age, 10 ± 4 years) served as control subjects. Two of 38 child relatives (5%) at risk of developing HCM fulfilled diagnostic criteria for HCM at inclusion. After 12 ± 1 years of follow-up, 2 of the 36 (6%; 95% confidence interval, 2-18) at-risk child relatives who were phenotype negative at inclusion had developed the HCM phenotype at 26 and 28 years of age. During follow-up, none of the child relatives experienced serious cardiac events. Participation in the screening program had no long-term negative psychological impact.

CONCLUSIONS

The penetrance of HCM in phenotype-negative child relatives at risk of developing HCM was 6% after 12 years of follow-up. The finding of phenotype conversion in the mid-20s warrants continued screening into adulthood. Forty-two percent of the child relatives were noncarriers, and repeat clinical follow-up could be safely limited to the remaining children.

Diagnostic yield, interpretation, and clinical utility of mutation screening of sarcomere encoding genes in Danish hypertrophic cardiomyopathy patients and relatives

The American Heart Association (AHA) recommends family screening for hypertrophic cardiomyopathy (HCM). We assessed the outcome of family screening combining clinical evaluation and screening for sarcomere gene mutations in a cohort of 90 Danish HCM patients and their close relatives, in all 451 persons. Index patients were screened for mutations in all coding regions of 10 sarcomere genes (MYH7, MYL3, MYBPC3, TNNI3, TNNT2, TPM1, ACTC, CSRP3, TCAP, and TNNC1) and five exons of TTN. Relatives were screened for presence of minor or major diagnostic criteria for HCM and tracking of DNA variants was performed. In total, 297 adult relatives (>18 years) (51.2%) fulfilled one or more criteria for HCM. A total of 38 HCM-causing mutations were detected in 32 index patients. Six patients carried two disease-associated mutations. Twenty-two mutations have only been identified in the present cohort. The genetic diagnostic yield was almost twice as high in familial HCM (53%) vs. HCM of sporadic or unclear inheritance (19%). The yield was highest in families with an additional history of HCM-related clinical events. In relatives, 29.9% of mutation carriers did not fulfil any clinical diagnostic criterion, and in 37.5% of relatives without a mutation, one or more criteria was fulfilled. A total of 60% of family members had no mutation and could be reassured and further follow-up ceased. Genetic diagnosis may be established in approximately 40% of families with the highest yield in familial HCM with clinical events. Mutation-screening was superior to clinical investigation in identification of individuals not at increased risk, where follow-up is redundant, but should be offered in all families with relatives at risk for developing HCM.

Genetic and phenotypic characterization of mutations in myosin-binding protein C (MYBPC3) in 81 families with familial hypertrophic cardiomyopathy: total or partial haploinsufficiency

Mutations in the MYBPC3 gene, encoding the sarcomere protein myosin-binding protein C, are among the most frequent causes of autosomal dominant familial hypertrophic cardiomyopathy (FHC). We studied the frequency, type, and pathogenetic mechanism of MYBPC3 mutations in an unselected cohort of 81 FHC families, consecutively enrolled at a tertiary referral center. Nine mutations, six of which were novel, were found in 10 (12.3%) of the families using single-strand conformation polymorphism and DNA sequencing. A frameshift mutation in exon 2 clearly suggests that haploinsufficiency is a pathogenetic mechanism in FHC. In addition, splice site mutations in exon 6 and intron 31, a deletion in exon 13, and a nonsense mutation in exon 25, all lead to premature termination codons, most likely causing loss of function and haploinsufficiency. Furthermore, there were two missense mutations (D228N and A833 T) and one in-frame deletion (DeltaLys813). A considerable intrafamilial variation in phenotypic expression of MYBPC3-based FHC was noted, and we suggest that mutations influencing stability of mRNA could play a role in the variable penetrance and expressivity of the disease, perhaps via partial haploinsuffciency.

One third of Danish hypertrophic cardiomyopathy patients have mutations in MYH7 rod region

Familial hypertrophic cardiomyopathy (FHC) is, in most cases, a disease of the sarcomere, caused by a mutation in one of 10 known sarcomere disease genes. More than 266 mutations have been identified since 1989. The FHC disease gene first characterized MYH7, encodes the cardiac beta-myosin heavy chain, and contains more than 115 of these mutations. However, in most studies, only the region encoding the globular head and the hinge region of the mature cardiac beta-myosin heavy chain have been investigated. Furthermore, most studies carries out screening for mutations in the most prevalent disease genes, and discontinues screening when an apparent disease-associated mutation has been identified. The aim of the present study was to screen for mutations in the rod region of the MYH7 gene in all probands of the cohort, regardless of the known genetic status of the proband. Three disease-causing mutations were identified in the rod region in four probands using capillary electrophoresis single-strand conformation polymorphism as a screening method. All mutations were novel: N1327K, R1712W, and E1753K. Two of the probands had already been shown to carry other FHC-associated mutations. In conclusion, we show that in the Danish cohort we find one third of all MYH7 mutations in the rod-encoding region and we find that two of the patients carrying these mutations also carry mutations in other FHC disease genes stressing the need for a complete screening of all known disease genes in FHC-patients.