ClinVar Genomic variation as it relates to human health

Nonsense variant predicted to result in protein truncation or nonsense mediated decay in a gene for which loss-of-function is a known mechanism of disease; Published functional studies using cardiomyocytes derived from induced pluripotent stem cells demonstrated this variant activates the nonsense-mediated decay pathway and results in aberrant calcium signaling and dysregulation of a set of other cardiac genes (Seeger et al., 2019); Not observed at significant frequency in large population cohorts (gnomAD); This variant is associated with the following publications: (PMID: 19666645, 23674513, 25335496, 26026863, 18761664, 22569109, 28214152, 30731207, 31006259, 31918855, 31513939, 30847666, 32480058, 22574137, 16679492, 25525159, 26936621, 15519027, 19858127, 27532257, 23396983, 24510615, 22857948, 24111713, 28794111, 28396031, 28005231, 23233322, 20624503, 21839045, 19356534, 19574547, 30165862, 28797094, 29447731, 30742251, 31323898, 33673806, 32665702, 33662488, 32746448, 20505798, 30586709)

This sequence change creates a premature translational stop signal (p.Arg943*) in the MYBPC3 gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in MYBPC3 are known to be pathogenic (PMID: 19574547). This variant is present in population databases (rs387907267, gnomAD 0.007%). This premature translational stop signal has been observed in individuals with hypertrophic cardiomyopathy (PMID: 19574547, 20505798, 20624503, 22574137, 22857948, 23233322, 24111713, 25335496). It is commonly reported in individuals of Dutch ancestry (PMID: 19574547, 20505798, 20624503, 22574137, 22857948, 23233322, 24111713, 25335496). ClinVar contains an entry for this variant (Variation ID: 37039). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may disrupt the consensus splice site. For these reasons, this variant has been classified as Pathogenic.

The variant is observed at an extremely low frequency in the gnomAD v2.1.1 dataset (total allele frequency: 0.001%). Stop-gained (nonsense): predicted to result in a loss or disruption of normal protein function through nonsense-mediated decay (NMD) or protein truncation. Multiple pathogenic variants are reported downstream of the variant. The variant has been reported at least twice as pathogenic with clinical assertions and evidence for the classification (ClinVar ID: VCV000037039 / PMID: 14563344 / 3billion dataset). Therefore, this variant is classified as pathogenic according to the recommendation of ACMG/AMP guideline.

The p.R943* pathogenic mutation (also known as c.2827C>T) located in coding exon 27 of the MYBPC3 gene, results from a C to T substitution at nucleotide position 2827. This changes the amino acid from an arginine to a stop codon within coding exon 27. This mutation has been reported in multiple unrelated probands with hypertrophic cardiomyopathy, having been reported as a Dutch founder mutation (Van Driest SL et al. J Am Coll Cardiol. 2004; 44(9):1903-10; Michels M et al. Neth Heart J. 2007;15(5):184-90; Michels M et al. JACC Cardiovasc Imaging. 2009;2(1):58-64; Christiaans I et al. Neth Heart J. 2010;18(5):248-54; Brito D et al. Rev Port Cardiol. 2012;31(9):577-87; Hathaway J et al. BMC Cardiovasc Disord, 2021 03;21:126). This mutation has been reported as occurring in the homozygous state and also with other alterations in patients with severe, early onset disease with and without other findings such as skeletal myopathy, non-compaction and congenital heart defects (Lekanne Deprez RH et al. J Med Genet. 2006;43(10):829-32; Tajsharghi H et al. J Med Genet. 2010;47(8):575-7; Berge KE et al. Clin Genet. 2014;86(4):355-60; Wessels MW et al. Eur J Hum Genet. 2015;23(7):922-8; van Velzen HG et al. Circ Cardiovasc Genet, 2017 Aug;10:[Epub ahead of print]). In addition to the clinical data presented in the literature, this alteration is expected to result in loss of function by premature protein truncation or nonsense-mediated mRNA decay. As such, this alteration is interpreted as a disease-causing mutation.

This variant has been reported in mutiple unrelated HCM patients in the literature (refs 1-6, below), and has also been shown to segregate with disease in multiple affected individuals in several unrelated families (Wessels et al (2015) Eur J Hum Genet 23(7)922-928). Several other clinical laboraties have also detected the variant in HCM patients referred for genetic testing (ClinVar variation ID: 37039). The variant has also been detected in control populations at a very low frequency which is compatible with the prevalence of disease (ExAC and gnomAD databases). In view of the evidence, this variant is pathogenic. - References - 1. Alders et al. (2003) Eur Heart J. 24(20):1848-53. 2. Van et al. (2004) J Am Coll Cardiol. 44(9):1903-10. 3. Christiaans et al. (2010) Neth Heart J. 18(5):248-54. 4. Millat et al. (2010) Eur J Med Genet. 53(5):261-7. 5. Yiu et al. (2012) PLoS One. 7(5):e36115. 6. Alfares et al. (2015) Genet Med.17(11):880-8. - Population Controls alleles / total (frequency): Exome Aggregation Consortium (ExAC) - 2/117632 (0.00001700), RBH healthy cohort - 0/2144 (0.0)

Variant summary: MYBPC3 c.2827C>T (p.Arg943X) results in a premature termination codon, predicted to cause a truncation of the encoded protein or absence of the protein due to nonsense mediated decay, which are commonly known mechanisms for disease. Truncations downstream of this position have been classified as pathogenic by our laboratory. The variant allele was found at a frequency of 1.2e-05 in 247124 control chromosomes (gnomAD). c.2827C>T has been reported in the literature in multiple individuals affected with Hypertrophic Cardiomyopathy (e.g. Van Driest_2004, Deprez_2006, Michels_2007, Berge_2013). These data indicate that the variant is very likely to be associated with disease. 15 clinical diagnostic laboratories have submitted clinical-significance assessments for this variant to ClinVar after 2014 and classified the variant as pathogenic. Based on the evidence outlined above, the variant was classified as pathogenic.

This variant changes 1 nucleotide in exon 27 of the MYBPC3 gene, creating a premature translation stop signal. This variant is expected to result in an absent or non-functional protein product. Functional RNA studies using cardiac tissue derived from a heterozygous carrier individual have shown that this variant causes a significant reduction in MYBPC3 mRNA levels (PMID: 33757590). This variant has been observed in over 20 unrelated individuals affected with hypertrophic cardiomyopathy (PMID: 16679492, 20624503, 22857948, 23233322, 24111713, 25335496, 27532257, 31006259, 31513939, 33757590, 36252119, 36835444) and is considered to be a founder mutation in the Dutch population (PMID: 20505798, 28794111). This variant has been reported to cause lethal cardiomyopathy or severe neonatal hypertrophic cardiomyopathy in individuals who were homozygous or compound heterozygous with another pathogenic mutation (PMID: 16679492, 24111713, 25335496, 30742251, 36178741). It has also been reported in two individuals affected with left ventricular noncompaction who both carried an additional different pathogenic variant (PMID: 31918855, 37963751), and in one individual affected with atrioventricular block (PMID: 35470684). This variant has been identified in 3/247124 chromosomes in the general population by the Genome Aggregation Database (gnomAD). Loss of MYBPC3 function is a known mechanism of disease. Based on available evidence, this variant is classified as Pathogenic.

This variant changes 1 nucleotide in exon 27 of the MYBPC3 gene, creating a premature translation stop signal. This variant is expected to result in an absent or non-functional protein product. Functional RNA studies using cardiac tissue derived from a heterozygous carrier individual have shown that this variant causes a significant reduction in MYBPC3 mRNA levels (PMID: 33757590). This variant has been observed in over 20 unrelated individuals affected with hypertrophic cardiomyopathy (PMID: 16679492, 20624503, 22857948, 23233322, 24111713, 25335496, 27532257, 31006259, 31513939, 33757590, 36252119, 36835444) and is considered to be a founder mutation in the Dutch population (PMID: 20505798, 28794111). This variant has been reported to cause lethal cardiomyopathy or severe neonatal hypertrophic cardiomyopathy in individuals who were homozygous or compound heterozygous with another pathogenic mutation (PMID: 16679492, 24111713, 25335496, 30742251, 36178741). It has also been reported in two individuals affected with left ventricular noncompaction who both carried an additional different pathogenic variant (PMID: 31918855, 37963751), and in one individual affected with atrioventricular block (PMID: 35470684). This variant has been identified in 3/247124 chromosomes in the general population by the Genome Aggregation Database (gnomAD). Loss of MYBPC3 function is a known mechanism of disease. Based on available evidence, this variant is classified as Pathogenic.

The p.Arg943X variant in MYBPC3 has been reported in >25 individuals with hypertrophic cardiomyopathy (HCM) and segregated with disease in 4 affected relatives in 4 families (Alders 2003 PMID: 14563344, Lekanne Deprez 2006 PMID: 16679492, Foksteun 2008 PMID: 18409188, Morita 2008 PMID: 18403758, Michels 2009 PMID: 19356534, Van Driest 2004 PMID: 15519027, Tajsharghi 2010 PMID: 19858127, Yiu 2012 PMID: 22574137, Wessels 2014 PMID: 25335496, LMM unpublished data). Several of these individuals carried an additional clinically significant variant and presented with early onset disease. This variant has been reported by other clinical laboratories in ClinVar (Variation ID 37039) and has also been identified in 0.006% (2/30444) of South Asian chromosomes by gnomAD (https://gnomad.broadinstitute.org/). This nonsense variant leads to a premature termination codon at position 943, which is predicted to lead to a truncated or absent protein. Loss of function of the MYBPC3 gene is an established disease mechanism in autosomal dominant HCM. In summary, this variant meets criteria to be classified as pathogenic for autosomal dominant HCM. ACMG/AMP criteria applied: PVS1, PS4, PP1, PM2_supporting.

Based on the classification scheme VCGS_Germline_v1.3.4, this variant is classified as Pathogenic. Following criteria are met: 0102 - Loss of function is a known mechanism of disease in this gene and is associated with hypertrophic cardiomyopathy 4 (HCM; MIM#115197). (I) 0108 - This gene is associated with both recessive and dominant disease. Dominant inheritance is frequently reported in adult onset conditions, however recessive inheritance results in a more severe early onset phenotype (OMIM). (I) 0115 - Variants in this gene are known to have variable expressivity (PMID: 32841044). (I) 0201 - Variant is predicted to cause nonsense-mediated decay (NMD) and loss of protein (premature termination codon is located at least 54 nucleotides upstream of the final exon-exon junction). (SP) 0251 - This variant is heterozygous. (I) 0302 - Variant is present in gnomAD (v3) <0.001 for a dominant condition (4 heterozygotes, 0 homozygotes). (SP) 0701 - Other null variants comparable to the one identified in this case have very strong previous evidence for pathogenicity. There are at least ten pathogenic NMD-predicted variants that have been reported (DECIPHER). (SP) 0801 - This variant has strong previous evidence of pathogenicity in unrelated individuals. This variant is a Dutch founder variant and has been classified as pathogenic by multiple diagnostic laboratories. This variant has also been reported to be compound heterozygous or homozygous in individuals with severe early-onset disease (ClinVar, PMID: 25335496). (SP) 1002 - This variant has moderate functional evidence supporting abnormal protein function. Cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs) heterozygous for this variant demonstrated aberrant calcium signalling and prolonged relaxation kinetics compared to WT cells, with homozygous iPSC-CMs demonstrating more severe impairment (PMID: 30586709). (SP) 1208 - Inheritance information for this variant is not currently available in this individual. (I) Legend: (SP) - Supporting pathogenic, (I) - Information, (SB) - Supporting benign

p.Arg943Stop in the MYBPC3 gene. In total the variant has been seen in at least 18 unrelated cases with weak segregation data. This variant was initially reported in Van Driest S et al. (2004) in one individual with HCM, in the presence of another missense variant (S166F) in the TNNI3 gene (note: p.S166F in TNNI3 is also currently considered a likely disease-causing variant). The authors noted that this patient, among the other 9 with multiple mutations identified, had significantly younger age of diagnosis, the most hypertrophy, and the highest incidence of myectomy and ICD placement when compared with single mutation carriers. This variant was absent from 200 control individuals screened in their study (100 African Americans and 100 European Americans). Michels et al. 2007 reports this p.Arg943Stop variant as a Dutch founder mutation, present in 15 of 100 Netherland families with HCM. Michels et al. 2009 subsequently reports this p.Arg943Stop variant in a study performing echocardiograms in genotyped HCM patients (8 of 27 with this particular variant), mutation carriers without LVH (7 of 27 family members), and 55 controls (this variant was present in 0 of 55 controls). Note, it is unclear whether these are overlapping with the 100 families reported in this group's 2007 study. Christiaans et al. 2010 also reports this variant as a founder mutation in the Netherlands. Tajsharghi et al. 2010 reports this variant seen in homozygous form in an infant with fatal cardiomyopathy and skeletal myopathy. The patient expressed the cardiac specific MyBPC isoform in skeletal muscle at transcript and protein levels. This was a similar finding in Deprez et al. 2005, where p.Arg943Stop was identified in a neonate with severe unexplained HCM who died within the first few weeks of life, in trans with a frameshift MYBPC3 variant. GeneDx reports that this variant has also been seen in multiple other unrelated individuals tested at GeneDx. This variant also segregates with disease in the patient's own family (as it is present in him, his father, and his aunt (all of whom have HCM)). This is a nonsense variant predicted to cause loss of normal protein function either through premature protein truncation or nonsense-mediated mRNA decay. Many other truncating or null variants have been identified in MYBPC3 in association with cardiomyopathy (ex. p.Trp792fs, p.Pro794fs, p.Lys1065fs, p.Cys1202fs, p.Pro1208fs, p.Trp1098ter, p.Glu1096ter, p.Cys1124ter, p.Gln1233ter). Furthermore, these types of variants in MYBPC3 are not seen in individuals without cardiomyopathy (Pan et al 2012). The variant was reported online in 3 of 122,257 individuals in the Genome Aggregation Consortium Dataset (gnomAD; http://gnomad.broadinstitute.org/), which currently includes variant calls on >140,000 unrelated individuals of African, Asian, European, Ashkenazi, Latino descent. Specifically, the variant was observed in 2 of 15,313 individuals of South Asian descent (MAF=0.006%) and 1 of 55,460 individuals of European descent. The phenotype of those individuals is not publicly available. The dataset is comprised of multiple cohorts, some of which were recruited from the general population, others were enriched for common cardiovascular disease. Note that other variants with strong evidence for pathogenicity have been seen at similar frequencies in datasets like this so this does not necessarily rule out pathogenicity (Pan et al 2012).