👤 Curtis D Klaassen

MYBPC3 is the most frequently affected gene in hypertrophic cardiomyopathy (HCM), which is an autosomal-dominant cardiac disease caused by mutations in sarcomeric proteins. Bi-allelic truncating MYBPC3 mutations are associated with severe forms of neonatal cardiomyopathy. We reprogrammed skin fibroblasts from a HCM patient carrying a heterozygous MYBPC3 truncating mutation into human induced pluripotent stem cells (iPSC) and used CRISPR/Cas9 to generate bi-allelic MYBPC3 truncating mutation and isogenic control hiPSC lines. All lines expressed pluripotency markers, had normal karyotype and differentiated into endoderm, ectoderm and cardiomyocytes in vitro. This set of three lines provides a useful tool to study HCM pathomechanisms. Show less

The underlying genetic mechanisms and early pathological events of children with primary cardiomyopathy (CMP) are insufficiently characterized. In this study, we aimed to characterize the mutational spectrum of primary CMP in a large cohort of patients ≤18 years referred to a tertiary center. Eighty unrelated index patients with pediatric primary CMP underwent genetic testing with a panel-based next-generation sequencing approach of 89 genes. At least one pathogenic or probably pathogenic variant was identified in 30/80 (38%) index patients. In all CMP subgroups, patients carried most frequently variants of interest in sarcomere genes suggesting them as a major contributor in pediatric primary CMP. In MYH7, MYBPC3, and TNNI3, we identified 18 pathogenic/probably pathogenic variants (MYH7 n = 7, MYBPC3 n = 6, TNNI3 n = 5, including one homozygous (TNNI3 c.24+2T>A) truncating variant. Protein and transcript level analysis on heart biopsies from individuals with homozygous mutation of TNNI3 revealed that the TNNI3 protein is absent and associated with upregulation of the fetal isoform TNNI1. The present study further supports the clinical importance of sarcomeric mutation-not only in adult-but also in pediatric primary CMP. TNNI3 is the third most important disease gene in this cohort and complete loss of TNNI3 leads to severe pediatric CMP. Show less

Dominant mutations in the MYH7 and MYBPC3 genes are common causes of inherited cardiomyopathies, which often demonstrate variable phenotypic expression and incomplete penetrance across family members. Biallelic inheritance is rare but allows gaining insights into the genetic mode of action of single variants. Here, we present three cases carrying a loss-of-function (LoF) variant in a compound heterozygous state with a missense variant in either MYH7 or MYBPC3 leading to severe cardiomyopathy with left ventricular noncompaction. Most likely, MYH7 haploinsufficiency due to one LoF allele results in a clinical phenotype only in compound heterozygous form with a missense variant. In contrast, haploinsufficiency in MYBPC3 results in a severe early-onset ventricular noncompaction phenotype requiring heart transplantation when combined with a de novo missense variant on the second allele. In addition, the missense variant may lead to an unstable protein, as overall only 20% of the MYBPC3 protein remain detectable in affected cardiac tissue compared to control tissue. In conclusion, in patients with early disease onset and atypical clinical course, biallelic inheritance or more complex variants including copy number variations and de novo mutations should be considered. In addition, the pathogenic consequence of variants may differ in heterozygous versus compound heterozygous state. Show less

Developmental regulation of gene expression is controlled by distinct epigenetic signatures catalyzed by various epigenetic modifiers. Little is known about the ontogeny and tissue distribution of these epigenetic modifiers. In the present study, we used a novel approach of RNA-sequencing to elucidate hepatic ontogeny and tissue distribution of mRNA expression of 142 epigenetic modifiers, including enzymes involved in DNA methylation/demethylation, histone acetylation/deacetylation, histone methylation/demethylation, histone phosphorylation and chromosome remodeling factors in male C57BL/6 mice. Livers from male C57BL/6 mice were collected at 12 ages from prenatal to adulthood. Many of these epigenetic modifiers were expressed at much higher levels in perinatal livers than adult livers, such as Dnmt1, Dnmt3a, Dnmt3b, Apobec3, Kat1, Ncoa4, Setd8, Ash2l, Dot1l, Cbx1, Cbx3, Cbx5, Cbx6, Ezh2, Suz12, Eed, Suv39h1, Suv420h2, Dek, Hdac1, Hdac2, Hdac7, Kdm2b, Kdm5c, Kdm7, Prmt1-5, Prmt7, Smarca4, Smarcb1, Chd4 and Ino80e. In contrast, hepatic mRNA expression of a few epigenetic modifiers increased during postnatal liver development, such as Smarca2, Kdm1b, Cbx7 and Chd3. In adult mice (60 d of age), most epigenetic modifiers were expressed at moderately (1-3-fold) higher levels in kidney and/or small intestine than liver. In conclusion, this study, for the first time, unveils developmental changes in mRNA abundance of all major known epigenetic modifiers in mouse liver. These data suggest that ontogenic changes in mRNA expression of epigenetic modifiers may play important roles in determining the addition and/or removal of corresponding epigenetic signatures during liver development. Show less

Left ventricular noncompaction of the myocardium (LVNC) has been recognized as a cardiomyopathy with a genetic etiology. Mutations in genes encoding sarcomere proteins were shown to be associated with LVNC. We evaluated the potential clinical impact of genetic analysis of sarcomere genes in patients with LVNC. We identified 5 mutations in cardiac myosin-binding protein C (MYBPC3) and 2 mutations in α-tropomyosin (TPM1) in a cohort of unrelated adult probands with isolated LVNC. The mutations in MYBPC3 and TPM1 and in 6 other previously reported sarcomere genes in this cohort resulted in a total of 18 (29%) heterozygous mutations in 63 probands. β-myosin heavy chain (MYH7) was the most prevalent disease gene and accounts for 13% of cases, followed by MYBPC3 (8%). Comparing sarcomere mutation-positive and mutation-negative LVNC probands showed no significant differences in terms of average age, myocardial function, and presence of heart failure or tachyarrhythmias at initial presentation or at follow-up. Familial disease was found in 16 probands of whom 8 were sarcomere mutation positive. Nonpenetrance was detected in 2 of 8 mutation-positive families with LVNC. Mutations in sarcomere genes account for a significant (29%) proportion of cases of isolated LVNC in this cohort. The distribution of disease genes confirms genetic heterogeneity and opens new perspectives in genetic testing in patients with LVNC and their relatives at high risk of inheriting the cardiomyopathy. The presence or absence of a sarcomere gene mutation in LVNC cannot be related to the clinical phenotype. Show less