Case1: 14 month, female

DiseaseAssertion: dilated cardiomyopathy

FamilyInfo:The three siblings' cases were born to consanguineous parents. They had DCM and died from decompensated heart failure around the age of 12 months

ParentalTesting: Sanger Sequencing determined the parents carried the variant at the heterozygous state (Figure 1)

CasePresentingHPOs: HP:0002094, HP:0002099, HP:0002098, HP:0002090,

CaseHPOFreeText:productive cough, and whining, wheezing, mitral and tricuspid regurgitation

CaseNotHPOs: NR

CaseNotHPOFreeText:no sign of ischemia,

CasePreviousTesting: cardiac ultrasound

Genotyping Method: sanger sequencing

FunctionalAnalysis: NR

Variant: TNNI3 (NM_000363.5): c.204delG;p.(Arg69AlafsTer8)

ClinVar: 179447

gnomAD: not found

Case1: Male, Infant, Tunisian

DiseaseAssertion: infantile-onset HCM and mitral valve dysplasia

FamilyInfo: Family with consanguinity in which four children had died before one year of age. The father (37 years old) and mother (27 years old) of the proband are consanguineously related. Two infants (VI:1 and VI:2) died at less than 30 days of age from cardiorespiratory arrest, and two (VI:3 and VI:4, proband) of them displayed abnormal cardiac findings on chest roentgenogram. While all four children displayed hepatomegaly and general hypotonia, VI:3 and VI:4 had a marked increase in heart size and died from refractory cardiogenic shock. The status of the MYL2 allele in siblings is unknown. The proband (fs/fs) was homozygous for the MYL2-fs allele while the parents were found to be heterozygous (fs/wt) carriers. The father (37 years old) and mother (27 years old) of the proband are consanguineously related, were asymptomatic from a cardiac standpoint and had normal cardiac anatomy and function as evaluated by an echocardiogram

ParentalTesting: Homozygous variant in the proband and that the parents are heterozygous carriers using Sanger DNA sequencing of the genomic region. Father (37 years old) and mother (27 years old) were asymptomatic from a cardiac standpoint and had normal cardiac anatomy and function as evaluated by an echocardiogram

CasePresentingHPOs: HP:0200128, HP:0001653, HP:0002092, HP:0001639, HP:0002240

CaseHPOFreeText: Showed a rapid decline in health and was treated for various periods in neonatal intensive care units. The patient also displayed severe mitral valve regurgitation with abnormal thickening of the mitral valve leaflets and pulmonary arterial hypertension. Post-mortem examination of the proband’s heart confirmed severe biatrial dilatation, significant biventricular hypertrophy with small ventricular cavities and severe mitral valve dysplasia

CaseNotHPOs: NR

CaseNotHPOFreeText: no gross developmental defects

CasePreviousTesting: No prior genetic testing reported before exome sequencing

Genotyping Method: Performed exome sequencing on the proband. Exome libraries were constructed using the Agilent SureSelectQXT Target Enrichment System for Illumina Multiplexed Sequencing Protocol (Agilent Technologies, CA). DNA libraries were captured with the Agilent Clinical Research Exome Kit. Paired-end 150 base pair reads were generated for exome-enriched libraries sequenced on the Illumina HiSeq 4000 to a targeted depth of 100× coverage

FunctionalAnalysis: Functional analysis performed. Immunohistochemical analysis of MYL2 expression in the proband’s ventricular myocardium shows a remarkable reduction in the expression of MYL2 as compared to control. Also, MYL2 mRNA was detected in the ventricle of the proband by RT-PCR. This suggests that the frameshift variant adversely affects the levels of MYL2 protein in the proband. Using immunoblot analysis, we observed that overexpression of the MYL2-fs variant was significantly reduced compared to stop-gain variants and the missense variant. When the H9c2 cells were treated with MG-132 after transfection with the MYL2-fs construct, the GFP signal corresponding to MYL2-fs was recovered. The in vitro experiments indicate that the MYL2-fs variant is not stable and that proteasome-mediated degradation of the translated product plays a key role in the instability of the protein. The overexpression of the fs variant identified in our proband or the MYL2-G162R missense variant failed to rescue the phenotype. Results reported in Figures 2, 3, and 4.

Variant: NM_000432.3:c.431_432delCT

ClinVar: NR

CAID: UnregisteredVariant

gnomAD: NR

AdditionalInfo: 4 siblings who died before 1 year of age but MYL2 genotyping was only confirmed in the proband (VI:4)

Case#: Pedigree I-1; 74-year-old Korean male; admitted for dyspnea (NYHA III), palpitations, and bilateral pitting leg edema over several months

DiseaseAssertion: Idiopathic restrictive cardiomyopathy (RCM) with biatrial enlargement, in a family with MYBPC3-related cardiomyopathy

FamilyInfo: Family history of heart disease with two affected daughters (II-2 and II-4), both heterozygous for the same variant and both diagnosed with HCM. Unaffected granddaughter (III-3) tested negative. Both daughters showed asymmetric septal hypertrophy on TTE (18 mm and 17 mm) with mildly dilated LA; daughter II-2 had grade I diastolic dysfunction and mild exertional chest discomfort. CMR confirmed reverse septal curvature hypertrophy consistent with HCM in both daughters, with no LGE in either.⁠

ParentalTesting: Not performed; the proband is the index case in generation I; his parents were not evaluated. Phase established only through the daughters and granddaughter.

CasePresentingHPOs:HP:0002094 (Dyspnea); HP:0001962 (Palpitations); HP:0001677 (Atrial fibrillation); HP:0001635 (Congestive heart failure); HP:0001639 (Hypertrophic cardiomyopathy); HP:0001698 (Pericardial effusion)

**CaseHPOFreeText: Exertional dyspnea NYHA class III, palpitations, and bilateral leg pitting edema for several months; dyspnea refractory to heart failure medication, with pulmonary venous congestion. ECG and Holter: atrial fibrillation with rare premature ventricular complexes. TTE: RCM with biatrial enlargement and small pericardial effusion. CMR: normal LV chamber size, borderline diffuse LV hypertrophy, very large atria, extensive transmural LGE in the apical wall and mid-myocardial patchy LGE in the ventricular septum. Coronary angiogram normal; no secondary cause of RCM found.⁠

CaseNotHPOs: HP:0000822 (Hypertension); HP:0000819 (Diabetes mellitus); HP:0001658 (Myocardial infarction); HP:0001678 (Atrioventricular block)

CaseNotHPOFreeText: Coronary angiogram normal, so no obstructive coronary disease. No secondary cause of RCM identified; no inflammatory, infiltrative, or systemic disease found. No AV block; the rhythm disturbance was atrial fibrillation.

CasePreviousTesting: Whole exome sequencing (Agilent SureSelect XT Human All Exon v5, Illumina HiSeq2500, GATK. Sanger sequencing of family members showed only the MYBPC3 variant tracked with disease; the other four (KALRN c.1702C>T, KCNH2 c.442C>T, SKI c.30T>G, TTN c.54293T>C) did not correlate with phenotype.⁠

Genotyping Method: WES in the proband, with annotation via dbNSFP and Ensembl VEP; Sanger sequencing confirmed the MYBPC3 frameshift in the proband (I-1), daughters II-2 and II-4, and its absence in granddaughter III-3 (Fig. 3B).⁠

FunctionalAnalysis: None performed. CMR showed extensive LGE in the apical LV, and the authors propose that advanced myocardial fibrosis in end-stage HCM can provoke myocardial atrophy, explaining the relatively normal LV chamber size with a predominantly restrictive phenotype hypothesis.⁠

Variant: MYBPC3 NM_000256.3:c.3313_3314insGG (p.Ala1105Glyfs*85); heterozygous frameshift insertion; absent from gnomAD and the Korean Reference Genome Database (accessed 8 November 2020)⁠.

ClinVar: 1473634

CAID: Not reported.

Gene:MYBPC3

HGNC: HGNC: 7551

PMID: 33803538

gnomAD: Absent per the authors' check of gnomAD as of 8 November 2020, and absent from KRGDB.

AdditionalInfo: Authors conclude the MYBPC3 frameshift is the pathogenic variant, with the same allele producing RCM in the proband and HCM in both daughters; an example of pleiotropy and variable expressivity within one family. The frameshift has previously been reported in Korean HCM. Poor-prognosis features in RCM cited by the authors: male sex, age over 70, high NYHA class, and LA dimension >60 mm.

Case#: 64-year-old male, non-smoker, first admitted June 2014; Russian family; died 2019 at age 69

DiseaseAssertion: MYBPC3-related cardiomyopathy with a predominantly restrictive phenotype in combination with left ventricular noncompaction (LVNC) and cardiac sarcoidosis

FamilyInfo: Son (39) and daughter (35) both heterozygous for the same variant and both have non-obstructive asymmetric HCM, with no LVNC on cardiac CT; both essentially asymptomatic on beta-blocker monotherapy. Five-year SCD risk 4.82% (son) and 2.07% (daughter); ICD implanted in the son, no shocks in three years. Authors mention another family of theirs with a father who died suddenly young and children with HCM and LVNC.

ParentalTesting: Not performed; the proband is the index case; his parents were not evaluated. Transmission to both children confirmed by Sanger.

CasePresentingHPOs:HP:0001639 (Hypertrophic cardiomyopathy)

CaseNotHPOs: Not reported

CasePreviousTesting: Not reported

Genotyping Method: Next-generation sequencing panel; variants confirmed by Sanger.

FunctionalAnalysis: None performed.

Variant 1: MYBPC3 NM_000256.3:c.278delA; heterozygous frameshift

Variant 2: KCNJ5 c.464G>A; heterozygous missense

ClinVar: Not reported.

CAID:Not reported.

gnomAD: No reported?

Gene:MYBPC3

PMID:36011256

Case#: Single proband ; 63-year-old female; palpitations at presentation July 2025; HCM diagnosis established at age 63

DiseaseAssertion: Hypertrophic cardiomyopathy (HCM) complicated by apical left ventricular aneurysm and mid-ventricular obstruction⁠

FamilyInfo: No family history of cardiac disease or sudden cardiac death at a young age reported. Both parents deceased (one of cancer, one of natural causes at age 92), neither with reported cardiovascular disease; proband has no siblings. Only first-degree relative is her son, who carries the KCNJ5 c.464G>A variant but not the MYBPC3 c.278delA variant, and has a normal echocardiogram with no myocardial hypertrophy. No pedigree beyond the son (Fig. 3B).⁠

ParentalTesting: Not performed; both parents deceased, no DNA available; authors state a valid familial segregation analysis could not be performed. Only one family member (son) was available for cascade Sanger screening.⁠

CasePresentingHPOs: HP:0001639 (Hypertrophic cardiomyopathy); HP:0001649 (Tachycardia), palpitations; HP:0001712 (Left ventricular hypertrophy).

CaseNotHPOFreeText: No history of hypertension, diabetes, or hyperlipidemia. Phenocopies excluded: no extra-cardiac manifestations of Fabry disease and GLA testing negative; cardiac amyloidosis excluded (no apical sparing, normal serum free light chains, negative serum protein electrophoresis and immunofixation); no significant coronary stenosis on coronary CT angiography. No QT prolongation or features of Andersen–Tawil syndrome on ECG.

CasePreviousTesting: Whole exome sequencing identified both variants; all rare and known variants validated by Sanger sequencing, with cascade Sanger screening in available one family member. No prior genetic testing reported before this episode.

Genotyping Method: Targeted region capture with next-generation high-throughput sequencing (whole exome, exonic plus flanking regions); variants confirmed by bidirectional Sanger sequencing. Cascade screening by Sanger in the son. MYBPC3 variant absent from 1000 Genomes, ESP6500, ExAC, and the Besuper local database. KCNJ5 variant absent from 1000 Genomes and ESP6500, ExAC frequency, absent from local Basenhall controls.⁠

FunctionalAnalysis: None performed; authors list absence of functional studies and lack of mRNA-level validation as limitations. MYBPC3 frameshift predicted to trigger nonsense-mediated decay.⁠

Variant: MYBPC3 NM_000256.3:c.278delA (p.Lys93ArgfsTer3); heterozygous; exon 2; novel, not in ClinVar or HGMD; classified Likely Pathogenic by ACMG (PVS1, PM2). Second variant: KCNJ5 NM_000256.3:c.464G>A (p.Arg155Gln); heterozygous; exon 2; novel, not in ClinVar or HGMD; classified VUS (PM2, PP3). Note the paper's KCNJ5 accession is written as NM_000256.3, which is the MYBPC3 transcript, most likely a typo in the article Pepper please conform for me the correct KCNJ5 accession

ClinVar: No ClinVar record for either variant; nearby KCNJ5 missense variants c.451G>A, c.452G>A, c.470T>G, and c.473C>G are documented as pathogenic/likely pathogenic for long QT syndrome or aldosteronism, and downstream frameshift/nonsense variants at the MYBPC3 locus are classified pathogenic or likely pathogenic.

CAID:Not found.

gnomAD: No allele frequency available, so no MAF to report.

PMID: 42428486

Gene: MYBPC3

HGNC: HGNC:7551

AdditionalInfo:Single-case report, no case numbering system used. Treated with dapagliflozin, metoprolol, rivaroxaban, and recombinant human BNP for 13 days, discharged on the first three; mexiletine added at 1-week follow-up for persistent palpitations. ICD recommended but declined due to financial constraints; 3-month follow-up showed good adherence with occasional palpitations and no serious arrhythmic events. Authors conclude MYBPC3 c.278delA is likely pathogenic for HCM, while the KCNJ5 variant shows no clinical phenotype in the proband or her son and may be incidental or a modifier.⁠

Case#: Pedigree III:2; male; HCM diagnosed clinically at age 39 (1998); heart transplant after progression to end-stage heart failure

DiseaseAssertion: Hypertrophic cardiomyopathy (HCM), progressed to end-stage heart failure with systolic dysfunction

FamilyInfo: No family history of heart disease reported at diagnosis; no known consanguinity. Parents deceased and unavailable for testing. 12 relatives genotyped: one brother (III:3) homozygous, seven first- and second-degree relatives heterozygous. All heterozygotes have normal ECG, normal echo, and no cardiac symptoms. Three children of generation IV (IV:7, IV:8, IV:9) still awaiting results.⁠

ParentalTesting: Not performed; both parents deceased. Absence of consanguinity stated but not genetically confirmed; parental phase therefore inferred rather than tested.

CasePresentingHPOs:HP:0001639 (Hypertrophic cardiomyopathy); HP:0002094 (Dyspnea); HP:0001658 (Myocardial infarction);HP:0001678 (Atrioventricular block)

CaseHPOFreeText: Exertional dyspnea at age 39 with systolic murmur; IVS 26 mm, posterior wall >16 mm, LVOT peak velocity 2.8 m/s. Pacemaker 1999, extracted 2010 for infection. 2013 circumflex occlusion treated with stent (cholesterol 6.8 mmol/L, LDL 4.6 mmol/L; former smoker). Septum 27 mm, moderate systolic dysfunction, NSVT on Holter → ICD. 2014 AF with severe dyspnea; on beta-blocker, ACE inhibitor, and aldosterone antagonist. 2016 VO₂max 14 mL/kg/min; LVEDP 24 mmHg rising to 38 with exercise, pulmonary pressure 56/27 rising to 70/… systolic. Biopsy: moderate interstitial fibrosis, focal hypertrophy and atrophy, no infiltrative disease.

CaseNotHPOs: HP:0000822 (Hypertension); HP:0000819 (Diabetes mellitus)

CaseNotHPOFreeText: BP normal throughout, no hypertension. No storage or infiltrative disease on biopsy. Spirometry normal. Narrow QRS, so CRT not indicated.

CasePreviousTesting: 84-gene cardiomyopathy NGS panel (MYBPC3 100% coverage); MLPA confirmed true homozygosity rather than hemizygous deletion; Sanger cascade in 12 relatives.

Genotyping Method: NGS panel followed by MLPA confirmation of homozygosity; Sanger for family cascade.

FunctionalAnalysis: None performed. Biopsy showed interstitial fibrosis with hypertrophy and atrophy, no infiltrative disease. Dominant-negative mechanism proposed, untested.

Variant: MYBPC3 NM_000256.3:c.2618C>A (p.Pro873His); homozygous missense; C7 domain. (Paper writes "c.2618 G>A" once, C>A is correct.)

ClinVar: Not stated; conflicting interpretations noted in the literature. Pepper please verifiy for me!

CAID: Not reported

gnomAD: AF 0.00006781 (14/206,446; 13/97,288 European non-Finnish) per the authors.

AdditionalInfo: ACMG Class 2 (likely pathogenic) heterozygous. Authors argue homozygosity drove progression to end-stage failure; alternative triggers considered, prior myocarditis (1989) and the 2013 infarct; but judged insufficient to explain severity.

PMID: 29663722 Gene: MYBPC3 HGNC: HGNC:7551

Case1: Male, Infant, ethnicity not stated

DiseaseAssertion: congenital fiber-type disproportion (CFTD) and fatal infantile cardiomyopathy

FamilyInfo: The father was a healthy 20-yr old with no particular medical concerns, and there was no family history of neuromuscular or genetic disorders on either side. Both parents confirmed as heterozygous carriers of the MYL2 c.188del variant by Sanger sequencing

ParentalTesting: Both parents were confirmed as heterozygous carriers of MYL2 c.188del p.(Asn63Metfs7) by Sanger sequencing. Father confirmed as heterozygous carrier of NEB c.25435C>T p.(Gln8479)

CasePresentingHPOs: HP:0001290, HP:0001252, HP:0001640, HP:0001638, HP:0001639

CaseHPOFreeText: Newborn exam revealed normal first and second heart sound with gallop rhythm and palpable liver at the right costal margin, as well as generalized hypotonia and diminished reflexes. Echocardiogram was performed at 11 d of age and revealed patent foramen ovale with left to right shunt and right atrial enlargement. At age 5 mo, the proband was admitted to hospital in decompensated heart failure and intubated on inotropic support. Echocardiography revealed left ventricular dilatation, mild to moderate mitral valve regurgitation, and left atrial enlargement, with left ventricular function moderately to severely decreased with shortening fraction of 12% and ejection fraction of 23%. A vastus lateralis biopsy performed at 5 mo of age because of persistent muscle weakness and hypotonia revealed variability in fiber size with checkerboard pattern of 1:1 ratio of type 1 and type 2 fibers exhibiting hypotrophy of type 1 fiber size in comparison to the type 2 fibers. high lactate level (7.8 mmol/L)

CaseNotHPOs: NR

CaseNotHPOFreeText: Gomori trichrome–stained light micrographs and electron microscopy (EM) showed no evidence of ragged red fiber or nemaline rods, and oxidative stains revealed no evidence of cores, targetoid, or target fibers. Normal serum creatine kinase level. Normal birth weight, length, and head circumference. There was no histopathologic evidence of Pompe disease and GAA enzyme-level testing was normal. Genetic testing for POLG and Noonan syndrome genes normal

CasePreviousTesting: Genetic testing was performed for DNA polymerase γ, catalytic subunit (POLG) and Noonan syndrome genes (PTPN11, SOS1, KRAS, RAF1, BRAF, MAP2K1, MAP2K2, and HRAS), all of which were normal. There was no histopathologic evidence of Pompe disease and GAA enzyme-level testing was normal. Muscular dystrophy was considered unlikely given the histopathologic findings and normal serum creatine kinase level.

Genotyping Method: Next-generation sequencing was performed by the Laboratory for Molecular Medicine (LMM) of Partners Healthcare Personalized Medicine using the Agilent SureSelect Design process. The gene panel utilized an all exon approach for 43 genes of interest for neuromuscular and cardiac conditions by targeting coding exons with bait out to coding sequence (CDS) ±65 bases. The complete coding regions of all genes were sequenced to average depth of 316 reads

FunctionalAnalysis: No functional analysis of the variant was performed

Variant: NM_000432.3:c.188del

ClinVar: NR

CAID: UnregisteredVariant

gnomAD: NR

AdditionalInfo: This case also has a heterozygous pathogenic NEB variant c.25435C>T p.(Gln8479*) inherited from the father, classified as pathogenic but considered unlikely to be a significant contributor to disease as no second NEB allele was identified.