Spongious Hypertrophic Cardiomyopathy in Patients With Mutations in the Four-and-a-Half LIM Domain 1 Gene

Novel FHL1 mutation variant identified in a patient with nonobstructive hypertrophic cardiomyopathy and myopathy - a case report

Background

Hypertrophic cardiomyopathy (HCM) is a genetic disorder mostly caused by sarcomeric gene mutations, but almost 10% of cases are attributed to inherited metabolic and neuromuscular disorders. First described in 2008 in an American-Italian family with scapuloperoneal myopathy, FHL1 gene encodes four-and-a-half LIM domains 1 proteins which are involved in sarcomere formation, assembly and biomechanical stress sensing both in cardiac and skeletal muscle, and its mutations are responsible for a large spectrum of neuromuscular disorders (mostly myopathies) and cardiac disease, represented by HCM, either isolated, or in conjunction with neurologic and skeletal muscle impairment. We thereby report a novel mutation variant in FHL1 structure, associated with HCM and type 6 Emery-Dreifuss muscular dystrophy (EDMD).

Case presentation

We describe the case of a 40 year old male patient, who was referred to our department for evaluation in the setting of NYHA II heart failure symptoms and was found to have HCM. The elevated muscular enzymes raised the suspicion of a neuromuscular disease. Rigid low spine and wasting of deltoidus, supraspinatus, infraspinatus and calf muscles were described by the neurological examination. Electromyography and muscle biopsy found evidence of chronic myopathy. Diagnosis work-up was completed by next-generation sequencing genetic testing which found a likely pathogenic mutation in the FHL1 gene (c.157-1G > A, hemizygous) involved in the development of X-linked EDMD type 6.

Conclusion

This case report highlights the importance of multimodality diagnostic approach in a patient with a neuromuscular disorder and associated hypertrophic cardiomyopathy by identifying a novel mutation variant in FHL1 gene. Raising awareness of non-sarcomeric gene mutations which can lead to HCM is fundamental, because of diagnostic and clinical risk stratification challenges.

Cardiac involvement in a cross-sectional cohort of myotonic dystrophies and other skeletal myopathies

Aims

Cardiac involvement in myopathies that primarily affect the skeletal muscle is variable and may be subtle, necessitating sensitive diagnostic approaches. Here, we describe the prevalence of cardiac abnormalities in a cohort of patients with skeletal muscle disease presenting at a tertiary care neuromuscular centre.

Methods and results

We systematically investigated patients with skeletal myopathies and comprehensively analysed their cardiac phenotype including 24 h electrocardiogram, echocardiography with strain analyses, contrast‐enhanced cardiac magnetic resonance imaging, and, if at increased risk of coronary artery disease, computed tomography coronary angiography. We prospectively screened 91 patients with diverse skeletal myopathies and enrolled 73 patients. The most pronounced cardiac involvement was present in patients with dystrophic myopathies (cardiac abnormalities in 59% of patients). We analysed myotonic dystrophies (n = 29) in more detail and found prolonged QRS (99.4 ± 15.6 vs. 91.5 ± 10.3 ms; P = 0.027) and QTc times (441.1 ± 28.1 vs. 413.0 ± 23.3 ms; P < 0.001) and increased left atrial size (27.28 ± 3.9 vs. 25.0 ± 3.2 mm/m²; P = 0.021) when compared with healthy controls. Left ventricular systolic function was reduced (ejection fraction < 55%) in 31% of myotonic dystrophies, while only 4% had an ejection fraction < 50%. Apical peak systolic longitudinal strain was slightly reduced (P = 0.023).

Conclusions

Screening for cardiac involvement in the skeletal muscle disease seems prudent particularly in patients with dystrophic myopathies. In the subset of myotonic dystrophy patients, QRS and QTc times as well as myocardial strain may be useful parameters. Their potential for predicting cardiac adverse events needs further evaluation.

Elevated Cardiac Troponin T in Patients With Skeletal Myopathies

BACKGROUND

Cardiac troponins are often elevated in patients with skeletal muscle disease who have no evidence of cardiac disease.

OBJECTIVES

The goal of this study was to characterize cardiac troponin concentrations in patients with myopathies and derive insights regarding the source of elevated troponin T measurements.

METHODS

Cardiac troponin T (cTnT) and cardiac troponin I (cTnI) concentrations were determined by using high sensitivity assays in 74 patients with hereditary and acquired skeletal myopathies. Patients underwent comprehensive cardiac evaluation, including 12-lead electrocardiogram, 24-h electrocardiogram, cardiac magnetic resonance imaging, and coronary artery computed tomography. cTnT and cTnI protein expression was determined in skeletal muscle samples of 9 patients and in control tissues derived from autopsy using antibodies that are used in commercial assays. Relevant Western blot bands were subjected to liquid chromatography tandem mass spectrometry for protein identification.

RESULTS

Levels of cTnT (median: 24 ng/l; interquartile range: 11 to 54 ng/l) were elevated (>14 ng/l) in 68.9% of patients; cTnI was elevated (>26 ng/l) in 4.1% of patients. Serum cTnT levels significantly correlated with creatine kinase and myoglobin (r = 0.679 and 0.786, respectively; both p < 0.001). Based on cTnT serial testing, 30.1% would have fulfilled current rule-in criteria for myocardial infarction. Noncoronary cardiac disease was present in 23%. Using cTnT antibodies, positive bands were found in both diseased and healthy skeletal muscle at molecular weights approximately 5 kDa below cTnT. Liquid chromatography tandem mass spectrometry identified the presence of skeletal troponin T isoforms in these bands.

CONCLUSIONS

Measured cTnT concentrations were chronically elevated in the majority of patients with skeletal myopathies, whereas cTnI elevation was rare. Our data indicate that cross-reaction of the cTnT immunoassay with skeletal muscle troponin isoforms was the likely cause.

Molecular autopsy and family screening in a young case of sudden cardiac death reveals an unusually severe case of FHL1 related hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a genetic cardiomyopathy with a prevalence of about 1:200. It is characterized by left ventricular hypertrophy, diastolic dysfunction and interstitial fibrosis; HCM might lead to sudden cardiac death (SCD) especially in the young. Due to low autopsy frequencies of sudden unexplained deaths (SUD) the true prevalence of SCD and especially of HCM among SUD remains unclear. Even in cases of proven SCD genetic testing is not a routine procedure precluding appropriate risk stratification and counseling of relatives.

METHODS

Here we report a case of SCD in a 19-year-old investigated by combined forensic and molecular autopsy.

RESULTS

During autopsy of the index-patient HCM was detected. As no other possible cause of death could be uncovered by forensic autopsy the event was classified as SCD. Molecular autopsy identified two (probably) pathogenic genetic variants in FHL1 and MYBPC3. The MYBPC3 variant had an incomplete penetrance. The FHL1 variant was a de novo mutation. We detected reduced FHL1 mRNA levels and no FHL1 protein in muscle samples suggesting nonsense-mediated mRNA decay and/or degradation of the truncated protein in the SCD victim revealing a plausible disease mechanism.

CONCLUSION

The identification of the genetic cause of the SCD contributed to the rational counseling of the relatives and risk assessment within the family. Furthermore our study revealed evidences for the pathomechanism of FHL1 mutations.

Cardiomyopathy and altered integrin-actin signaling in Fhl1 mutant female mice

X-linked scapuloperoneal myopathy (X-SM), one of Four-and-a-half LIM 1 (FHL1) related diseases, is an adult-onset slowly progressive myopathy, often associated with cardiomyopathy. We previously generated a knock-in mouse model that has the same mutation (c.365 G > C, p.W122S) as human X-SM patients. The mutant male mouse developed late-onset slowly progressive myopathy without cardiomyopathy. In this study, we observed that heterozygous (Het) and homozygous (Homo) female mice did not show alterations of skeletal muscle function or histology. In contrast, 20-month-old mutant female mice showed signs of cardiomyopathy on echocardiograms with increased systolic diameter [wild-type (WT): 2.74 ± 0.22 mm, mean ± standard deviation (SD); Het: 3.13 ± 0.11 mm, P < 0.01; Homo: 3.08 ± 0.37 mm, P < 0.05) and lower fractional shortening (WT: 31.1 ± 4.4%, mean ± SD; Het: 22.7 ± 2.5%, P < 0.01; Homo: 22.4 ± 6.9%, P < 0.01]. Histological analysis of cardiac muscle revealed frequent extraordinarily large rectangular nuclei in mutant female mice that were also observed in human cardiac muscle from X-SM patients. Western blot demonstrated decreased Fhl1 protein levels in cardiac muscle, but not in skeletal muscle, of Homo mutant female mice. Proteomic analysis of cardiac muscle from 20-month-old Homo mutant female mice indicated abnormalities of the integrin signaling pathway (ISP) in association with cardiac dysfunction. The ISP dysregulation was further supported by altered levels of a subunit of the ISP downstream effectors Arpc1a in Fhl1 mutant mice and ARPC1A in X-SM patient muscles. This study reveals the first mouse model of FHL1-related cardiomyopathy and implicates ISP dysregulation in the pathogenesis of FHL1 myopathy.

The sarcomeric M-region: a molecular command center for diverse cellular processes

The sarcomeric M-region anchors thick filaments and withstands the mechanical stress of contractions by deformation, thus enabling distribution of physiological forces along the length of thick filaments. While the role of the M-region in supporting myofibrillar structure and contractility is well established, its role in mediating additional cellular processes has only recently started to emerge. As such, M-region is the hub of key protein players contributing to cytoskeletal remodeling, signal transduction, mechanosensing, metabolism, and proteasomal degradation. Mutations in genes encoding M-region related proteins lead to development of severe and lethal cardiac and skeletal myopathies affecting mankind. Herein, we describe the main cellular processes taking place at the M-region, other than thick filament assembly, and discuss human myopathies associated with mutant or truncated M-region proteins.

A novel single nucleotide splice site mutation in FHL1 confirms an Emery-Dreifuss plus phenotype with pulmonary artery hypoplasia and facial dysmorphology

We describe a Danish family with an, until recently, unknown X-linked disease with muscular dystrophy (MD), facial dysmorphology and pulmonary artery hypoplasia. One patient died suddenly before age 20 and another was resuscitated from cardiac arrest at the age of 28. Linkage analysis pointed to a region of 25 Mb from 123.6 Mb to 148.4 Mb on chromosome X containing over 100 genes. Exome sequencing identified a single nucleotide splice site mutation c.502-2A > T, which is located 5' to exon 6 in the gene encoding four and a half LIM domain 1 (FHL1) protein. FHL1 expresses three main splice variants, known as FHL1A, FHL1B and FHL1C. In healthy individuals, FHL1A is the predominant splice variant and is mainly found in skeletal and cardiac muscle. The FHL1 transcript profiles from two affected individuals were investigated in skin fibroblasts with quantitative real-time PCR. This demonstrated loss of isoform A and B, and an almost 200-fold overexpression of isoform C confirming that lack of FHL1A and overexpression of FHL1C results in an extended phenotype of EDMD as recently shown by Tiffin et al. [2013].

Fhl1 W122S causes loss of protein function and late-onset mild myopathy

A member of the four-and-a-half-LIM (FHL) domain protein family, FHL1, is highly expressed in human adult skeletal and cardiac muscle. Mutations in FHL1 have been associated with diverse X-linked muscle diseases: scapuloperoneal (SP) myopathy, reducing body myopathy, X-linked myopathy with postural muscle atrophy, rigid spine syndrome (RSS) and Emery-Dreifuss muscular dystrophy. In 2008, we identified a missense mutation in the second LIM domain of FHL1 (c.365 G>C, p.W122S) in a family with SP myopathy. We generated a knock-in mouse model harboring the c.365 G>C Fhl1 mutation and investigated the effects of this mutation at three time points (3-5 months, 7-10 months and 18-20 months) in hemizygous male and heterozygous female mice. Survival was comparable in mutant and wild-type animals. We observed decreased forelimb strength and exercise capacity in adult hemizygous male mice starting from 7 to 10 months of age. Western blot analysis showed absence of Fhl1 in muscle at later stages. Thus, adult hemizygous male, but not heterozygous female, mice showed a slowly progressive phenotype similar to human patients with late-onset muscle weakness. In contrast to SP myopathy patients with the FHL1 W122S mutation, mutant mice did not manifest cytoplasmic inclusions (reducing bodies) in muscle. Because muscle weakness was evident prior to loss of Fhl1 protein and without reducing bodies, our findings indicate that loss of function is responsible for the myopathy in the Fhl1 W122S knock-in mice.

Isolated X-linked hypertrophic cardiomyopathy caused by a novel mutation of the four-and-a-half LIM domain 1 gene

BACKGROUND

Hypertrophic cardiomyopathy with severe left ventricular diastolic dysfunction has been associated with marked exercise intolerance and poor prognosis. However, molecular pathogenesis of this phenotype remains unexplained in a large proportion of cases.

METHODS AND RESULTS

We performed whole exome sequencing as an initial genetic test in a large Czech family with 3 males affected by nonobstructive hypertrophic cardiomyopathy with severe left ventricular diastolic dysfunction in end-stage disease. A novel frameshift mutation of four-and-a-half LIM domain 1 gene (FHL1) (c.599_600insT; p.F200fs32X) was detected in these individuals. The mutation does not affect transcription, splicing, and stability of FHL1 mRNA and results in production of truncated FHL1 protein, which is contrary to heart tissue homogenate not detectable in frozen tissue sections of myocardial biopsy of affected males. The identified mutation cosegregated also with abnormal ECG and with 1 case of apical hypertrophic cardiomyopathy in heterozygous females. Although skeletal muscle involvement is a common finding in FHL1-related diseases, we could exclude myopathy in all mutation carriers.

CONCLUSIONS

We identified a novel FHL1 mutation causing isolated hypertrophic cardiomyopathy with X-chromosomal inheritance.

Left ventricular hypertrophy caused by a novel nonsense mutation in FHL1

Emery Dreifuss muscular dystrophy (EDMD) is a hereditary muscular disorder, characterized by contractures, progressive muscular wasting and cardiac involvement. The majority of EDMD patients harbor mutations in the lamin A/C (LMNA) and emerin (STA) genes. Emerging data implicate mutations in FHL1 (four and a half LIM protein 1) gene, located in chromosome Xq26, in EDMD pathogenesis. FHL1 is mainly expressed in striated and cardiac muscle, and plays an important role in sarcomeric protein synthesis, maintenance of cellular integrity, intracellular signaling and genetic transcription pathways. We report the identification of a novel nonsense mutation in FHL1 gene, associated with left ventricular hypertrophy and a family history of stroke and sudden cardiac death. The management implications of this diagnosis are also discussed.