A 76-year-old man with previous history of hypertension, dyslipidemia, and paroxysmal atrial fibrillation was diagnosed with obstructive HCM at the age of 52 years. He was known to have a brother diagnosed with HCM at the age of 55 years (II-6) and a sister who died suddenly of unknown cause at the age of 49 years (II-5). The family pedigree is shown in Figure 1.

Figure 1.

Family pedigree. G+: genotype positive; G-: genotype negative. Arrow: proband.

Before follow-up in our clinic, he had undergone myectomy and mitral valve replacement for left ventricular outflow tract (LVOT) obstruction refractory to medical therapy at the age of 60 years. He has been in New York Heart Association (NYHA) class II-III heart failure (HF) ever since, treated with oral anticoagulants, angiotensin-converting enzyme inhibitors, spironolactone and beta-blockers. After four years of uneventful follow-up, he had an embolic stroke. His ECGs showed atrial fibrillation, ST-segment depression and biphasic T-waves in V4-V6, III and aVF (Figure 2A). The transthoracic echocardiograms showed severe septal hypertrophy (interventricular septum 19 mm, inferolateral wall 13 mm), left ventricular ejection fraction (LVEF) 55%, increased filling pressures (E/e’ ratio 31) with no exercise-induced intraventricular gradient, and a normally functioning mechanical mitral valve (Figure 3A). Some of the 24-hour Holter recordings during follow-up showed non-sustained ventricular tachycardia (NSVT) as the only American College of Cardiology Foundation/American Heart Association risk factor,12 and his last estimated European Society of Cardiology SCD risk score5,13 was 5.0% at five years. Cardiac magnetic resonance (CMR) showed asymmetric HCM (MWT 24 mm), normal systolic function (LVEF 61%) and focal late gadolinium enhancement (LGE) in the hypertrophied segments (Figure 4A).

Figure 2.

Electrocardiograms: (A, Case 1): atrial fibrillation, ST-segment depression and biphasic T-waves in V4-V6, III and aVF; (B, Case 2): sinus rhythm, short PR interval, T-wave inversion in III, flat T-wave in aVF, biphasic T-wave in II, V4-V6; (C, Case 3): sinus rhythm, short PR interval, electrocardiographic criteria for left ventricular hypertrophy, ST-segment depression and T-wave inversion in V4-V6, II, III and aVF.

Figure 3.

Transthoracic echocardiogram, parasternal long-axis, 4-chamber and 2-chamber views: (A, Case 1): asymmetric hypertrophic cardiomyopathy (HCM) (maximum wall thickness [MWT] 16 mm) and normal prosthetic mitral function; (B, Case 2): asymmetric HCM (MWT 22 mm); (C, Case 3): asymmetric HCM (MWT 21 mm); (D, Case 4): asymmetric HCM (MWT 22 mm).

Figure 4.

Cardiac magnetic resonance imaging (4-chamber, 2-chamber and short-axis cine and late gadolinium enhancement (LGE) views): (A, Case 1): asymmetric hypertrophic cardiomyopathy (HCM) with late gadolinium enhancement (LGE) in the hypertrophied segments; (B, Case 2): asymmetric HCM with LGE in the hinge points; (C, Case 3): asymmetric HCM with LGE in the hinge points.

The proband underwent clinical genetic testing in 2009, which was reported negative for sarcomeric mutations in MYH7, MYBPC3, TNNT2, TNNI3, MYL2, MYL3, ACTC1, TMP1, and CSRP3, extended three years later to PRKAG2, GLA and LAMP2, also negative. The search for mutations in each of these genes, in an accredited clinical laboratory, was performed for the entirety of the coding region, including exon-intron boundaries (canonical splice sites), using polymerase chain reaction and direct Sanger sequencing. This method has 99% sensitivity in detecting nucleotide substitutions and short insertion-deletions (indels).

In 2017, DNA extracted from the proband's blood was sent to Novogene Corporation for whole-genome sequencing (the rationale for this decision is explained in the discussion). A capture library from New England Biolabs was used for whole-genome amplification and sequencing was carried out on an Illumina HiSeq X Ten platform, with 150 bp paired-end reads and a mean read depth of 50. Reads were pre-processed with Trim Galore version 0.4.4 to remove sequencing adapters and to filter the sequences with a minimum Phred quality score of 20. Most of the reads (∼98.8%) were kept for downstream alignment against the hg19 reference genome using Burrows-Wheeler Aligner (BWA) mem version 0.7.15. The Genome Analysis Toolkit version 4.0.1.2 (GATK4) was applied to mark duplicates and to calculate genome coverage. Variant calling was performed with Strelka2 version 2.8.4 at a mean genome coverage of 40×. After an initial filtering step, 4 862 291 variants (both single-nucleotide polymorphisms and small indels) were obtained. Further analysis revealed a heterozygous intronic variant, c.1227-13G>A (rs397515893), in the MYBPC3 gene (intron 14), classified as likely pathogenic.

The proband's relatives were then genotyped for this variant by Sanger sequencing. As shown in Figure 1, the variant was present in all four affected members and not present in the three non-affected members who were tested.

The proband's oldest daughter (Figure 1) was referred for clinical screening at the age of 38 years. At that time, she was in NYHA class II and had had previous episodes of exertional angina. The physical examination revealed a harsh systolic murmur at the lower left sternal border. The ECG showed sinus rhythm, short PR interval, T-wave inversion in DIII, flat T wave in aVF and biphasic T wave in DII and V4-V6 (Figure 2B). The transthoracic echocardiogram confirmed the diagnosis, showing asymmetric HCM involving the septum and anterior wall (MWT 22 mm), with no systolic anterior motion (SAM) of the mitral valve or intraventricular gradient at rest or with Valsalva maneuver or exercise (Figure 3B). As well as confirming the echocardiographic findings, CMR revealed mid-cavity obliteration and LGE matching the hypertrophic segments and the left ventricular-right ventricular (LV-RV) hinge points (Figure 4B). She was started on a beta-blocker. At that time, she had no risk factors for sudden cardiac death. Two years later she developed short episodes of palpitations and 24-hour Holter monitoring showed non-sustained ventricular tachycardia. She had an estimated SCD risk of 5.9% at five years (age: 42 years, MWT: 22 mm, left atrial size: 48 mm, maximum LVOT gradient: 2 mmHg; family history of SCD: no, non-sustained ventricular tachycardia: yes, syncope: no) and received a single-chamber implantable cardioverter-defibrillator (ICD) for primary prevention of SCD. Three years later she was in NYHA class III HF. The transthoracic echocardiogram showed a restrictive diastolic filling pattern (E/e’ ratio 18), diminished longitudinal systolic function (septal S’ 3 cm/s and lateral S’ 6 cm/s; global longitudinal strain -11%) and hypokinesia of the hypertrophic segments despite normal ejection fraction; she also had incomplete SAM but no significant mitral regurgitation. She never developed significant intraventricular gradients during follow-up, including on treadmill exercise echocardiography. Under spironolactone, her functional capacity improved and the next transthoracic echocardiogram also showed an improvement in LV filling pressures (E/e’ ratio 9). She has had no malignant arrhythmia since.

The proband's middle son (Figure 1) was first studied in the setting of familial screening at 35 years of age. Although he was asymptomatic, his transthoracic echocardiogram confirmed the diagnosis of asymmetric HCM, with hypertrophy particularly involving the septum (MWT 21 mm) and the anterior and inferior walls, mild mitral regurgitation and no other relevant findings (Figure 3C). He underwent treadmill exercise echocardiography, which showed no exercise-induced obstruction. The baseline ECG was unremarkable except for evidence of left atrial abnormality. The 24-hour Holter ECG findings were also unremarkable. CMR showed asymmetric HCM (MWT 24 mm), with normal systolic function (LVEF 75%) and focal LGE in the LV-RV hinge points (Figure 4C). After two years, he developed NYHA class II HF symptoms and exercise-induced dizziness. The ECG at that time showed sinus rhythm, short PR interval, slow R-wave progression in the precordial leads and T-wave inversion in the inferior and lateral leads. The transthoracic echocardiogram revealed increased LV filling pressures (mean E/e’ ratio 16). He was started on spironolactone and remained in NYHA class II HF. Three years later, although clinically stable, he developed electrocardiographic criteria for left ventricular hypertrophy (LVH), as well as a short-PR interval, deep S waves in the right precordial leads, ST-segment depression and T-wave inversion in V4-V6 and the inferior leads (Figure 2C). The transthoracic echocardiogram was similar to the previous one. During follow-up, 24-hour Holter monitoring showed no relevant arrhythmia and the echocardiogram revealed no significant intraventricular obstruction, including on treadmill stress testing. His estimated SCD at last clinical follow-up was 3.1% at five years (age: 39 years, MWT: 25 mm, left atrial size: 50 mm, maximum LVOT gradient: 2 mmHg; family history of SCD: no, non-sustained ventricular tachycardia: no, syncope: no).

This niece of the proband (Figure 1) was mostly followed in another center abroad. She was diagnosed with HCM at the age of 24 and at early presentation she was in NYHA class II HF. At that time, 24-hour Holter monitoring showed no NSVT. She was referred to our clinic during her second pregnancy (11 years after diagnosis). The ECG showed sinus rhythm, short PR interval, electrocardiographic criteria for LVH, QS complexes in DIII and aVF and T-wave inversion in V2-V5. Her transthoracic echocardiogram (38th week of pregnancy) showed asymmetric HCM affecting the septum (MWT 22 mm), SAM of the mitral valve but no significant gradient, normal systolic function and increased filling pressures (E/e’ ratio 21) (Figure 3D). The transthoracic echocardiogram showed normal filling pressures after delivery (E/e’ ratio 6).

Cases 5 and 6 were niece and nephew of the proband (Figure 1), enrolled in the clinical screening. Their electrocardiograms and echocardiograms showed no signs of HCM.