Article Text

Original article
A founder MYBPC3 mutation results in HCM with a high risk of sudden death after the fourth decade of life
  1. Chiara Calore1,
  2. Marzia De Bortoli2,
  3. Chiara Romualdi2,
  4. Alessandra Lorenzon2,
  5. Annalisa Angelini1,
  6. Cristina Basso1,
  7. Gaetano Thiene1,
  8. Sabino Iliceto1,
  9. Alessandra Rampazzo2,
  10. Paola Melacini1
  1. 1Department of Cardiac, Thoracic, and Vascular Sciences, University of Padua, Padua, Italy
  2. 2Department of Biology, University of Padua, Padua, Italy
  1. Correspondence to Dr Alessandra Rampazzo, Department of Biology, University of Padua, Via G. Colombo 3, Padua 35131, Italy; alessandra.rampazzo{at}unipd.it

Abstract

Background Mutations in the cardiac myosin binding protein C (MYBPC3) gene account for a significant proportion of patients affected with hypertrophic cardiomyopathy (HCM). The aim of this study was to evaluate the penetrance and the impact of a frequent founder MYBPC3 mutation on HCM clinical expression and prognosis.

Methods and results Mutation screening of MYBPC3 gene was performed in 97 HCM probands. Nineteen (19.5%) resulted to be carriers of the founder p.F305Pfs*27 mutation and other 45 mutation carriers were identified during the evaluation of 14 families. Eleven (38%) mutation carriers were diagnosed between ages 30 years and 40 years. Disease penetrance was incomplete (64.4%), age-related and was greater in men than women (85% vs 48%, p=0.009). Probands carrying the founder mutation exhibited highest prevalence of non-sustained ventricular tachycardia (63% vs 22%, p=0.003; 63% vs 23%, p=0.01) and implantable cardioverter-defibrillator (58% vs 17%, p=0.001; 58% vs 18%, p=0.005) when compared with probands without MYBPC3 mutations or carrying other MYBPC3 mutations. Reduced survival due to sudden cardiac death (SCD) or aborted SCD occurred more frequently after the fourth decade of life in probands carrying p.F305Pfs*27 mutation than those without MYBPC3 mutations (32% vs 15%, p=0.01).

Conclusions p.F305Pfs*27 mutation carriers have a high probability to develop the disease between ages 30 years and 40 years with a significant major risk if they are men. This founder mutation is associated with an increase of SCD/aborted SCD events after the fourth decade of life.These findings are of relevant importance for management and clinical decision-making in patients with HCM.

  • Cardiomyopathy
  • Clinical genetics

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Introduction

Hypertrophic cardiomyopathy (HCM) is a common genetic disorder with an autosomal dominant inheritance, a variable expressivity and an incomplete penetrance. It is considered the most common cause of sudden cardiac death (SCD) in young people and in competitive athletes.1 ,2

In the last 20 years more than 1400 distinct mutations in over 18 genes have been identified in HCM.3 ,4 Worldwide, most causative mutations are localised in sarcomeric genes encoding mainly for the myosin-binding protein C (MYBPC3) gene and the β myosin heavy chain (MYH7) gene.3 ,4 Recent reports suggest that MYBPC3 gene mutations could be inherited in more than 60 million people.5 ,6 The high frequency of MYBPC3 mutations could be explained in part by the high occurrence of founder mutations in this gene, as reported by different groups.7–13

Variability in the onset and prognosis of the disease have been recorded in several longitudinal studies focused on the progression of cardiac phenotypes associated with MYBPC3 mutations in different populations, although initially MYBPC3 mutations have been associated with late onset, mild hypertrophy, lower incidence of SCD and a relatively benign clinical course.6 ,14 Information on genotype/phenotype correlation is still weak, and different mutations in the same gene seem to behave differently in terms of clinical presentation and outcomes.4 Founder mutations give the unique opportunity to assess clinical relationships between a specific mutation and phenotype.

We report the identification of a frequent founder MYBPC3 mutation in 19 Italian HCM probands and in 45 family members. The aim of the study was to evaluate the penetrance and impact of this genotype on HCM clinical expression and prognosis.

Methods

Study population

Study population included 97 Italian consecutive HCM index patients evaluated in Padua University HCM Center.

HCM was diagnosed according to the 2011 American College of Cardiology Foundation/American Heart Association (ACCF/AHA) HCM guidelines15 and relatives were considered phenotypically affected if they had a maximal left ventricular wall thickness (MLVWT) ≥13 mm at echocardiography.16

All the participants provided written informed consent before inclusion in the study.

Clinical evaluation

All patients underwent clinical evaluation, including family and personal history, physical examination, blood pressure, resting 12-lead ECG, two-dimensional Doppler echocardiography and 24-h Holter monitoring at study entry and once a year during follow-up. Family history of HCM was considered positive in the presence of clinico-echocardiographic evidence of a familial HCM phenotype (≥two affected family members).

Echocardiographic studies were performed with commercially available Philips SONOS 5500 instruments with a 3 MHz transducer. Two-dimensional images and M-mode echocardiograms of atrial and ventricular cavities were obtained in multiple cross-sectional planes, with the transducer in standard positions according to the recommendations of the American Society of Echocardiography.17 ,18 Left ventricular (LV) ejection fraction (EF) was calculated from two-dimensional images with modified Simpson's formula or area-length method.17 Invasive coronary angiography was performed in all patients who survived cardiac arrest, in those with sustained ventricular tachyarrhythmia or with typical exertional chest pain and before cardiac transplant. A subgroup of patients underwent cardiac magnetic resonance (CMR) study,19 including cine, black blood Turbo Spin Echo (TSE) Fat Suppressed T2-weighted sequences (to detect any abnormal signal consistent with oedema) and late gadolinium enhancement (LGE) images. They were examined using 1.5-T scanner (Harmony, Siemens, Erlangen, Germany) implemented with cardiological software (MRease SYNGO 2002B, Siemens). All the images were acquired during the same imaging session using a four channel phased-array receiver coil during repeated breath-holds of varying duration and were independently analysed by two observers using a 17-segment model. The follow-up data were obtained during regular outpatient visits at about 12-month intervals, and cardiac events were collected. For survival analysis, adverse cardiac events included SCD or aborted SCD (aSCD), deaths related to refractory heart failure (HF) and cardiac transplantation. SCD was defined as any natural death occurring instantaneously or within 1 h from symptoms onset. Aborted SCD was defined as successful cardiopulmonary resuscitation/defibrillation for cardiac arrest due to ventricular fibrillation or appropriate implantable cardioverter-defibrillator (ICD) intervention, defined as an ICD shock delivered in response to ventricular tachycardia or ventricular fibrillation and documented by stored intracardiac ECG data. HF death was defined as progressive cardiac decompensation over ≥1 year before death or transplant, which frequently required hospitalisation, particularly if complicated by pulmonary oedema.

HCM sudden death risk calculator (http://doc2do.com/hcm/webHCM.html)20 was used to estimate the 5 years SCD mortality rate in all probands and affected relatives by entering values collected at study entry for each patient.

Genetic analysis

Probands were screened for MYBPC3 mutations by denaturing high-performance liquid chromatography (DHPLC, Transgenomic, Nebraska, USA) and direct sequencing. Detected variants were confirmed at least in two independent PCRs and sequencing runs. Genetic variants were annotated according to the cDNA and protein reference sequences NM_000256 and NP_000247.

MYBPC3 mutation carriers were screened for additional mutations in MYH7 (exons 3–40), TNNI3 (exons 1–8) and TNNT2 (exons 8–16) genes, in order to detect multiple mutation carriers. Only probands carrying a single MYBPC3 mutation were subsequently considered for the study.

All variants not listed in dbSNPs database (http://www.ncbi.nlm.nih.gov/projects/SNP/), 1000Genomes Project database (http://www.1000genomes.org) and Exome Variant Server (http://evs.gs.washington.edu/EVS/) or showing in these databases a minor allele frequency (MAF) ≤0.1% were assessed in 200 ethnically matched healthy and unrelated subjects (400 chromosomes). Based on the frequency of HCM in the general population (1:500), the estimated number of individuals in the 1000Genomes Project database and in the Exome Variant Server (6500 subjects) that can be expected to be affected by HCM, is 2 and 13, respectively (MAF=0.1%).21

A genetic variant was considered as a possible causal mutation on the basis of its absence in controls or showing a MAF ≤0.1% and, in the presence of a missense mutation, when also a damaging effect was predicted by at least two out of three appropriate programs (Polyphen2: http://genetics.bwh.harvard.edu/pph2/, SIFT: http://sift.bii.a-star.edu.sg/www/SIFT_BLink_submit.html, ConDel: http://bg.upf.edu/condel). Missense variants considered not deleterious for protein function by the prediction programs and intronic and synonymous changes absent in controls or showing a MAF ≤0.1% were considered unclassified variants (UVs). All available family members were screened for the founder mutation identified in the probands.

Haplotype analysis

To investigate if the frameshift mutation carriers have a common haplotype, four polymorphic markers (D11S1344, D11S1252, D11SA1 and D11S395) in close proximity to MYBPC3 locus and nine SNPs (rs3729986, rs3218719, rs11570050, rs11570051, rs3729989, rs2856650, rs11570078, rs1052373 and rs2290146) within the MYBPC3 gene were analysed. D11SA1 marker is a polymorphic dinucleotide repeat identified at position chr11.hg19:g.(47741121)_(47741167) on chromosome 11p11.2 (Human Genome Browser, http://genome.ucsc.edu/). It was amplified using the following primers: D11SA1F 5′CCAGTTGATTGTT GGTCTTAGGC3′, D11SA1R 5′ACCCTGCTTGACTGAAATA TA3′. The polymorphic markers cover 5.11 Mb around the MYBPC3 gene.

The most likely haplotype was constructed and in seven probands the phase of the haplotype was confirmed by family analysis.

Statistical methods

Quantitative continuous variables are reported as means±SDs. Categorical variables are reported as frequencies or percentages. The χ2 test or Fisher's exact test was used to compare frequencies, whereas differences in continuous variables were evaluated with Student's t test and/or one-way ANOVA (ANalysis Of VAriance). In order to evaluate the association between the combinations of more than one clinical variable and patient class, we used a multivariate logistic regression.

The cumulative probability of experiencing a cardiac event during the lifetime was determined by using date of birth as the start point for the time-to-event analysis. Subjects were censored at the time of their first event or the time of their last clinical follow-up. Event-free rates were calculated with the Kaplan-Meier method. Logrank tests were used to assess differences in event-free rates between groups.

Multivariate Cox proportional hazards modelling was used to estimate the HRs for SCD, HF and adverse cardiac events among genotyped patient groups. Independent risk factors for SCD and HF determinants with p<0.05 at univariate analysis were included in the model.

All statistical analyses were performed with R statistical software (V. 2.15.3 available at http://www.r-project.org).

Patients harbouring UVs or multiple mutations were not considered.

Results

Patient population and genetic analysis

Clinical characteristics of 97 HCM index patients are summarised in table 1. Sixty-nine (71%) patients were male. More than half (56%) had a positive family history for HCM and 24% had SCD family history. Age at diagnosis widely ranged from 1 year to 77 years (mean 31 years). Age at last exam was 46±17 years with a mean follow-up duration of 10 years (range 6 months–29 years). Two-thirds of patients were symptomatic at diagnosis and at last follow-up. In asymptomatic patients (33%), HCM was accidentally diagnosed during ECG screening for sport eligibility (20%) and during echocardiographic evaluation for cardiac murmurs and/or other cardiovascular abnormalities (13%). There was a mild increase in atrial diameter between diagnosis and last examination (42 mm vs 47 mm, p=0.02); whereas other clinicomorphological parameters did not show significant changes.

Table 1

Clinical characteristics of 97 index patients with HCM at diagnosis and at last evaluation

During the follow-up, ICD was implanted in 25 out of 97 index cases for primary prevention, 10 patients died of SCD, 7 were successfully resuscitated from cardiac arrest due to ventricular fibrillation (aSCD), 4 died from refractory HF and 10 patients were transplanted. A total of 31 HCM-related adverse cardiac events, including SCD, aSCD, HF deaths and transplant were recorded (table 1).

Sixteen different MYBPC3 mutations, including 10 missense, 2 frameshift, 2 splice-site, 2 nonsense were identified in 39 (39.8%) probands (see online supplementary table S1).

Two patients were compound heterozygotes for MYBPC3 mutations: one patient carried the c.506–2A>C and the p.V771M mutations, whereas the other one showed the p.P371R and the p.K1065Qfs*12 mutations. Moreover, four nucleotide substitutions defined as UVs were identified as well (see online supplementary table S2).

Among MYBPC3 mutation carriers, no one showed additional mutations in MYH7, TNNI3 and TNNT2 genes. A patient carrying the p.A364T mutation in MYBPC3 gene had an UV in TNNI3 gene (c.371+6G>A).

The MYBPC3 p.F305Pfs*27 mutation was found in 19 (19.5%) index cases (14 men and 5 women). Among 79 relatives belonging to 14 apparently unrelated families, 45 (20 men and 25 women) resulted to be mutation carriers and 29 of them (17 men and 12 women) had phenotypical expression of HCM (figure 1).

Figure 1

Pedigree of families with hypertrophic cardiomyopathy carrying the p.F305Pfs*27 mutation. Probands are indicated by an arrow.

Haplotype analysis

To investigate whether probands carrying the p.F305Pfs*27 mutation have a common ancestor, we performed haplotype analysis using four polymorphic markers and nine MYBPC3 intragenic SNPs. A shared haplotype, spanning 1.29 Mb, D11S1252(155)-rs3729986(G)-rs3218719(G)-rs11570050(delC)-rs11570051(C)-rs3729989(A)-MUT-rs2856650(T)-rs11570078(G)-rs2290146(C)-D11SA1(255) was found in all probands carrying the p.F305Pfs*27 mutation, indicating that a common founder was likely in these families. The legitimacy of the constructed haplotype was confirmed in seven patients analysing their family members and enabling the determination of correct phase.

Clinical findings of p.F305Pfs*27 mutation carriers

Characteristics of the 19 index cases (74% men) carrying MYBPC3 p.F305Pfs*27 mutation are detailed in table 2 and summarised in tables 3 and 4.

Table 2

Clinical and echocardiographic data of the 19 index cases carrying the p.F305Pfs*27 MYBPC3 mutation

Table 3

Characteristics of affected p.F305Pfs*27 mutation carriers

Table 4

Clinical features of probands categorised according to their MYBPC3 genotype

Ages at diagnosis ranged from 6 years to 60 years (mean age 36±16 years, median age 32 years) and mean age at last exam was 54±14 years (median age 49 years; range 31–76 years). The mean follow-up period was 13±8 years (range 3–29 years). Most of them (84%) were symptomatic, despite pharmacological therapy. At first echocardiographic evaluation they had mild to massive grade HCM (MLVWT ranged from 15 mm to 37 mm) whereas at last follow-up two cases evolved towards LV dilatation with wall thinning (respectively, 5 mm and 10 mm), systolic dysfunction and severe diastolic dysfunction. End-stage HCM (with EF<50%) was present at entry in two patients and in two further patients progressive deterioration of EF occurred during the follow-up. Atrial fibrillation complicated the clinical course in 21% of probands and non-sustained ventricular tachycardia (NSVT) was recorded in 63% of them.

Among the end-stage group, a patient (table 2, #7) whose first manifestation of the disease was an aSCD at 48 years, was transplanted after 10 years of follow-up. The explanted heart was available and showed LV chamber dilatation and anterior septum and free wall thinning due to extensive transmural fibrosis in spite of normal coronary arteries at angiography. In such patient a myocardial bridge of the left anterior descending coronary artery may have promoted extensive scarring and loss of contractile function associated with LV chamber remodelling (figure 2).

Figure 2

A patient with hypertrophic cardiomyopathy (HCM) carrying the p.F305Pfs*27 MYBPC3 mutation. Male HCM proband (#7 in table 2) with aborted sudden cardiac death (aSCD) requiring implantable cardioverter-defibrillator implantation as first disease manifestation at the age of 48 years, and evolution to end-stage HCM requiring heart transplantation at the age of 58 years. (A) Echocardiographic short-axis view in end diastole showing thinning and akinesia of anteroseptal wall (B). Heart removed at transplantation: mid-ventricular transverse section showing the anteroseptal transmural scarring, with apical aneurysm and endocardial thrombus stratification (white arrow). (C) RV free wall showing increased interstitial fibrosis and disarray of groups of myocytes. Trichrome stain ×20. (D) LV posterior free wall showing the typical pattern of hypertrophy and disarray of single myocytes. Trichrome stain ×40. (E) Histological section of the myocardial bridge: note the myocardium encircling the left anterior descending coronary artery (black arrow) and the fibrous tissue underneath (asterisk). Trichrome stain ×3. LV, left ventricle; RV, right ventricle.

Clinical evaluation was also performed in 45 family members carrying the p.F305Pfs*27 mutation.

Since the diagnostic criterion for relatives is MLVWT ≥13 mm, 29 patients were affected. Twenty-one (72%) had the diagnosis in the process of family screening, five were referred to our centre due to the presence of symptoms (three of them were already diagnosed elsewhere), whereas three came to our attention for ECG abnormalities detected during athletic screening or pregnancy.

Clinical follow-up was available in 27/29 phenotype positive carriers (mean 11±9 years, median 9 years, range 6 months–30 years). Characteristics of affected carriers and comparison between probands and relatives and between men and women are shown in table 3.

Despite no statistically significant differences found in age at diagnosis, age at last exam, prevalence of hypertension and follow-up duration (13±8 years vs 11±9 years, p>0.1), probands had more severe LV hypertrophy (23±7 mm vs 19±5 mm, p=0.035), lower EF (54±10% vs 61±9%, p=0.008), and were more symptomatic (84% vs 48%, p=0.01) than affected relatives. They also experienced NSVT (63% vs 28%, p=0.01) more frequently and underwent ICD implantation (58% vs 14%, p=0.001). Moreover, risk of SCD at 5 years was higher in probands than in affected relatives (6.3±3.5 vs 3.8±2.6, p=0.01).

Kaplan-Meier survival analysis showed worse prognosis in probands compared with relatives (p=0.02 for SD/aSD and p=0.01 for all adverse cardiac events). Concerning gender differences, men had higher LV end-diastolic volume (67±18 ml/m2 vs 53±18 ml/m2, p=0.017) whereas women had more frequently obstructive and end-stage forms (53% vs 13%, p=0.003); no other gender-related significant differences were found in clinical presentation, echocardiographic findings and prognosis.

End-stage HCM forms (with EF <50%) were found in four women and two men carrying the MYBPC3 mutation and all were symptomatic (NYHA class II or more). All but one of these patients were older than 45 years (mean age 56 years), confirming that the evolution towards systolic dysfunction is progressive and usually becomes evident late in life. Significant LV outflow gradient (>30 mm Hg at rest) was more commonly found in affected women, at entry (35% vs 13%, p=0.07) and at last control (29% vs 6%, p=0.03). Obstructive forms were symptomatic (chest pain, dyspnoea and/or syncope) in all patients, with no gender differences.

The remaining 16 family members carrying the p.F305Pfs*27 mutation, during a mean follow-up period of 3±6 years, were completely asymptomatic and without LV hypertrophy at echocardiography. In only one case pathological Q waves were present at ECG. Phenotype-negative carriers were younger than affected family members (40±15 vs 56±19, p=0.007) and most frequently were women (13/16, 81%, vs 12/29, 41%, p=0.01).

p.F305Pfs*27 mutation penetrance

Overall disease penetrance was 75% in all mutation carriers and 64.4% in relatives undergoing familial evaluation. The penetrance remained incomplete, but increased with age during all life and was significantly higher in men, considering all mutation carriers (91% vs 57%, p=0.001) and only the family members (85% vs 48%, p=0.009). Taking into account that 74% of probands carrying the frameshift mutation are men, penetrance according to gender was analysed only in relatives. Gender differences in HCM penetrance are significant along all life and the major increase in penetrance (20%) occurs between 30 years and 40 years in both genders (see figure 3 and online supplementary table S3).

Figure 3

Disease penetrance in male and female p.F305Pfs*27 mutation carriers. HCM, hypertrophic cardiomyopathy.

Since hypertension is considered a HCM trigger,15 we investigated whether hypertension could contribute to the different penetrance between men and women. Among the 45 relatives carrying the founder MYBPC3 mutation, all with hypertension had phenotypical expression of HCM (with typical asymmetrical LV hypertrophy) and no one with hypertension was found among healthy carriers. Seven (41%) out of 17 affected men and 4 (33%) out of 12 affected women had hypertension. However, this higher prevalence in affected men than in affected women is not statistically significant (p=0.7).

CMR in p.F305Pfs*27 mutation carriers

CMR was performed in eight probands, four affected relatives and two healthy carriers of the p.F305Pfs*27 mutation. All probands and affected relatives showed LGE with variable extension (from a single patchy area to a diffuse pattern). Myocardial oedema (increased signal in T2-weighted images) was found in 6 (50%) out of 12 affected mutation carriers. All the eight probands and three affected relatives experienced NSVT or sustained ventricular tachycardia.

CMR was also performed in two young healthy carriers of the MYBPC3 founder mutation (12 years and 17 years old) who underwent a deep diagnostic screening for sport eligibility: in the former a focal area of LGE was found in the inferior septum and in the latter myocardial crypts were detected in inferoseptal and inferolateral walls. No arrhythmic complications were reported in these healthy carriers.

Genotype-phenotype correlations and outcome

According to genetic analysis results, index cases were grouped as follows: Group 0, including 54 patients without MYBPC3 mutations; Group 1, including 19 carriers of the MYBPC3 p.F305Pfs*27 mutation; Group 2, including 17 patients with other MYBPC3 mutations. Patients carrying double mutations (n=2) or UV (n=5) were not considered for statistical analysis.

Comparison among the three genetic groups is reported in table 4. Probands carrying the founder mutation exhibited the highest prevalence of HCM family history (95% vs 52%, p=0.002; 95% vs 41%, p=0.002), of NSVT (63% vs 22%, p=0.003; 63% vs 23%, p=0.01), of ICD implantation (58% vs 17%, p=0.001; 58% vs 18%, p=0.005) and an increased risk of SCD at 5 years (6.3±3.5 vs 4.1±3.3, p=0.03; 6.3±3.5 vs 4.1±1.9, p=0.09), when compared respectively with Group 0 and Group 2 patients.

Univariate (Kaplan-Meier) survival analysis did not show significant differences in survival for patients belonging to the three different genetic groups.

By multivariate (Cox proportional hazards model) analysis, taking into account age and other risk factors for cardiac death in HCM, patients harbouring p.F305Pfs*27 mutation (Group 1) exhibited higher risk of SCD/aSCD than patients without MYBPC3 mutations (Group 0) (p=0.01) (figure 4). In particular, despite similar survival in young age, Group 1 patients had a reduced survival after the fourth decade of life when compared with Group 0. No survival differences were found when Group 1 vs Group 2 and Group 2 vs Group 0 were compared (figure 4).

Figure 4

Comparison of long-term natural history between probands carrying the p.F305Pfs*27 mutation, probands carrying other MYBPC3 mutations and probands negative for MYBPC3 mutations. Survival free from cardiac SD/aSD. SD, sudden death; aSD, aborted sudden death.

Discussion

Founder mutations have been described in different HCM populations7–13 and contribute in large part (10–25% to 58%) to the detected mutations in the origin countries.10 ,13

The p.F305Pfs*27 truncating mutation, previously described in two patients (one French and one Italian)8 ,22 was found in the current study in 19 (19.5%) probands. A shared haplotype was identified in these patients, all coming from the Veneto region in the north-east of Italy, supporting the hypothesis that the mutation arose from a common ancestor. To the best of our knowledge, it represents the most frequent founder mutation in MYBPC3 gene in Italian patients with HCM.

This mutation, detected in a total of 64 subjects belonging to 14 families, gave the unique opportunity to study its clinical profile and penetrance.

Sixteen (84%) out of 19 probands carrying the founder mutation were symptomatic with broad heterogeneity and severity of hypertrophy. Four of them had or developed LV systolic dysfunction (EF <50%). Atrial fibrillation complicated the clinical course in 21% of probands and NSVT was recorded in 63% of them. Among 45 family members carrying the founder mutation, 29 fulfilled the diagnostic criteria for HCM and, despite no differences in age at diagnosis or at last exam, affected relatives displayed less severe phenotype and better prognosis when compared with the probands. Although early reports suggested that HCM commonly develops in adolescence and early adulthood,1 the majority of relatives (87.5%) were diagnosed after the age of 20 years, as recently reported for other MYBPC3 mutation carriers.9

Among the 48 affected mutation carriers, 8 sudden (or aborted) cardiac deaths and 4 HF deaths accounting for a total of 12 (25%) adverse cardiac events occurred during the follow-up, with overall annual mortality rate of 2%, higher than that previously described in MYBPC3 carriers9 and in the general population of patients with HCM.2

Taking into account that 74% of probands carrying the p.F305Pfs*27 mutation are men, we analysed the disease penetrance, according to gender, only in relatives. Of note is that HCM penetrance was significantly higher in men (85%) than women (48%) and was related to age. Interestingly, the estimated penetrance in women was less than 50% during the entire lifetime, whereas penetrance in men was still higher than 50% from the third decade of life. Gender difference in penetrance showed its major imbalance trough 30–40 years with a mutation penetrance in men fourfold higher than in women (57.1% vs 13.3%). Moreover between 30 years and 40 years of age there was a maximum increase (20–22%) in penetrance in both genders (men: from 57% to 77%; women: from 13.3% to 35%), whereas after the reproductive age the tendency to enhance continued but was lower (3–7%).

That female p.F305Pfs*27 mutation carriers are to some degree protected from developing HCM is of great relevance for genetic counselling and therapeutic considerations. However, despite the lower penetrance, when HCM is phenotypically expressed, severity of disease and prognosis is relatively higher in women compared with men; thus a periodic clinical follow-up is recommended in both genders and also in adulthood. Accordingly to previous studies,23 ,24 the severe progression of the disease in affected women may be explained in part by the greater prevalence of obstruction and systolic dysfunction.

Lower penetrance among women may be the result of biological differences and/or of lesser exposure to environmental factors hypothesised to trigger HCM in susceptible individuals, such as sustained vigorous athletic activity. The existence of biological gender-specific factors, such as postmenopausal endocrine changes, has been hypothesised to influence the clinical course of HCM.23 ,25–28 Moreover there is evidence suggesting that differential gene regulation in men and women, particularly in relation to sex steroid-responsive genes, can influence the expression of human phenotypes, including disease traits.29 ,30

Incomplete and age-related penetrance was previously reported in other founder MYBPC3 mutations, but it was not fully evaluated according to gender. The p.V592fs*8 mutation identified in Japanese families showed a penetrance of 100% in subjects ≥50 years and of 65% in those <50 years.12 The founder IVS23+1G>A mutation showed a 50% penetrance in Spanish patients at 46 years of age, with a tendency to manifest the disease earlier in men (42 years) than women (50 years).11 Among the French IVS20-2A>G mutation carriers there is no age threshold but rather a regular increase in the disease penetrance, which was 62% at the average age of 47 years.8 Three founder MYBPC3 mutations were identified in the Dutch population; many mutation carriers manifested LV hypertrophy only in adulthood, whereas some of them were still without significant hypertrophy in their 80s.10

Accordingly to previous studies, describing MYBPC3 founder mutations,8 ,10–12 clinical manifestation associated with p.F305Pfs*27 mutation is not benign, with a significant subset of patients presenting with SCD and HF late in life. The late onset of life-threatening HCM complications (delayed beyond the reproductive age) allows the transmission of the founder mutation to next generations, leading to its spread in the population.

To better analyse the clinical features and outcome associated with the p.F305Pfs*27 founder mutation, we compared three different groups of HCM Italian probands: those with the p.F305Pfs*27 mutation, those with other MYBPC3 mutations and those without MYBPC3 mutations. Phenotypical expression of the p.F305Pfs*27 mutation seems to be associated with an arrhythmic profile, characterised by the highest prevalence of non-sustained ventricular tachycardia and ICD implantation compared with the other two groups. Available data of CMR, performed in a limited number of probands carrying the MYBPC3 founder mutation, suggest a possible association between LGE and the high frequency of ventricular arrhythmic events.

Moreover, patients carrying the p.F305Pfs*27 mutation had a poor outcome after the fourth decade of life, due to a significant proportion of probands who experienced SCD or aSCD when compared with patients without MYBPC3 mutations. We are aware that this last mentioned group, even if genetically homogeneous for the absence of coding MYBPC3 mutations, may include a number of patients with mutations in any of several other HCM genes (known or yet-to-be identified as HCM-susceptibility genes). Although it would have been advantageous to make a comparison among genetically homogeneous groups, the genetic heterogeneity inherent in this disorder limits such analysis.

In conclusion, p.F305Pfs*27 founder mutation accounts for about 20% of HCM cases in our cohort. Patients carrying this mutation were more likely to manifest the disease between ages 30 years and 40 years, in particular if they are men, with a high risk of sudden death after the fourth decade of life. These findings will contribute to an early molecular diagnosis in HCM patients and are of relevant importance for clinical practice and genetic counselling.

Acknowledgments

The authors thank the patients and their families for participation in this study.

References

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Footnotes

  • CC and MDB contributed equally.

  • Contributors All authors have contributed significantly to the paper and revised it critically for important intellectual content. CC and PM were in charge of the clinical management of all patients with HCM; they collected, analysed, interpreted the data and drafted the manuscript. MDB performed the mutation screening and the haplotype analysis in patients with HCM, analysed and interpreted the data, and drafted the manuscript. CR performed the statistical analysis. AL designed the PCR primers and set up the conditions used in the mutation screening. AA, CB, GT, SI contributed clinical samples, and histological and patient data. AR and PM planned the original design of the study, supervised and coordinated the whole project and cowrote the paper. All authors read and approved the final manuscript.

  • Funding This work was supported by the Italian Ministry for Scientific and Technological Research (MURST-COFIN 2008, Number 20083EWHYR_002 to PM) and the University of Padua (grant CPDA133979/13 to AR).

  • Competing interests None.

  • Ethics approval The ethics committee review board of the University of Padua Medical School-Azienda Ospedaliera (Padua, Italy) approved the study protocol, in compliance with Helsinki declaration.

  • Provenance and peer review Not commissioned; externally peer reviewed.