Phenotypic expression and clinical outcomes in a South Asian PRKAG2 cardiomyopathy cohort

Results of comprehensive genetic testing in patients presenting to a multidisciplinary inherited heart disease clinic in India

OBJECTIVES

This study aims to analyze the results of comprehensive genetic testing in patients presenting to a dedicated multidisciplinary inherited heart disease clinic in India.

METHODS

All patients presenting to our clinic from August 2017 to October 2023 with a suspected inherited heart disease and consenting for genetic testing were included. The probands were grouped into familial cardiomyopathies namely hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), arrhythmogenic cardiomyopathy (ACM) and peripartum cardiomyopathy (PPCM), channelopathies namely congenital long QT syndrome (LQTS) and Brugada syndrome (BrS), and heritable connective tissue disorder namely Marfan Syndrome (MFS). Next generation sequencing (NGS) was used, and pre-test and post-test counseling were provided to probands and cascade screening offered to relatives.

RESULTS

Mean age of the subjects (n = 77; 48 probands, 29 relatives) was 43 ± 18 years, 68 % male and 44 % symptomatic, with 36 HCM, 3 DCM, 3 ACM, 1 PPCM, 3 LQTS, 1 BrS and 1 MFS probands. The diagnostic yield of NGS-based genetic testing was 31 %; variants of uncertain significance (VUS) were identified in 54 %; and 15 % were genotype-negative. Twenty-nine relatives from 18 families with HCM (n = 12), DCM (n = 3), ACM (n = 2) and MFS (n = 1) underwent genetic testing. The genotype positive probands/relatives and VUS carriers with strong disease phenotype and/or high risk variant were advised periodic follow-up; the remaining probands/relatives were discharged from further clinical surveillance.

CONCLUSIONS

Genetic testing guides treatment and follow-up of patients with inherited heart diseases and should be carried out in dedicated multidisciplinary clinics with expertise for counseling and cascade screening of family members.

Human Genetics of Cardiac Arrhythmias

Inherited forms of cardiac arrhythmias mostly are rare diseases (prevalence <1:2000) and considered to be either "primary electrical heart disorders" due to the absence of structural heart abnormalities or "cardiac ion channel disorders" due to the myocellular structures involved. Precise knowledge of the electrocardiographic features of these diseases and their genetic classification will enable early disease recognition and prevention of cardiac events including sudden cardiac death.The genetic background of these diseases is complex and heterogeneous. In addition to the predominant "private character" of a mutation in each family, locus heterogeneity involving many ion channel genes for the same familial arrhythmia syndrome is typical. Founder pathogenic variants or mutational hot spots are uncommon. Moreover, phenotypes may vary and overlap even within the same family and mutation carriers. For the majority of arrhythmias, the clinical phenotype of an ion channel mutation is restricted to cardiac tissue, and therefore, the disease is nonsyndromic.Recent and innovative methods of parallel DNA analysis (so-called next-generation sequencing, NGS) will enhance further mutation and other variant detection as well as arrhythmia gene identification.

Hypertrophic Cardiomyopathy and Ventricular Preexcitation in the Young: Cause and Accessory Pathway Characteristics

BACKGROUND

The cause of hypertrophic cardiomyopathy (HCM) in the young is highly varied. Ventricular preexcitation (preexcitation) is well recognized, yet little is known about the specificity for any cause and the characteristics of the responsible accessory pathways (AP).

METHODS

Retrospective cohort study of patients <21 years of age with HCM/preexcitation from 2000 to 2022. The cause of HCM was defined as isolated HCM, storage disorder, metabolic disease, or genetic syndrome. Atrioventricular AP (true AP) were distinguished from fasciculoventricular fibers (FVF) using standard invasive electrophysiology study criteria. AP were defined as high risk if any of the following were <250 ms: shortest preexcited RR interval in atrial fibrillation, shortest paced preexcited cycle length, or anterograde AP effective refractory period.

RESULTS

We identified 345 patients with HCM and 28 (8%) had preexcitation (isolated HCM, 10/220; storage disorder, 8/17; metabolic disease, 5/19; and genetic syndrome, 5/89). Six (21%) patients had clinical atrial fibrillation (1 with shortest preexcited RR interval <250 ms). Twenty-two patients underwent electrophysiology study which identified 23 true AP and 16 FVF. Preexcitation was exclusively FVF mediated in 8 (36%) patients. Five (23%) patients had AP with high-risk conduction properties (including ≥1 patient in each etiologic group). Multiple AP were seen in 8 (36%) and AP plus FVF in 10 (45%) patients. Ablation was acutely successful in 13 of 14 patients with recurrence in 3. One procedure was complicated by complete heart block after ablation of a high-risk midseptal AP. There were significant differences in QRS amplitude and delta wave amplitude between groups. There were no surface ECG features that differentiated AP from FVF.

CONCLUSIONS

Young patients with HCM and preexcitation have a high likelihood of underlying storage disease or metabolic disease. Nonisolated HCM should be suspected in young patients with large QRS and delta wave amplitudes. Surface ECG is not adequate to discriminate preexcitation from a benign FVF from that secondary to potentially life-threatening AP.

Intrafamilial Phenotypical Variability Linked to PRKAG2 Mutation-Family Case Report and Review of the Literature

PRKAG2 syndrome (PS) is a rare, early-onset autosomal dominant phenocopy of sarcomeric hypertrophic cardiomyopathy (HCM), that mainly presents with ventricular pre-excitation, cardiac hypertrophy and progressive conduction system degeneration. Its natural course, treatment and prognosis are significantly different from sarcomeric HCM. The clinical phenotypes of PRKAG2 syndrome often overlap with HCM due to sarcomere protein mutations, causing this condition to be frequently misdiagnosed. The syndrome is caused by mutations in the gene encoding for the γ2 regulatory subunit (PRKAG2) of 5′ Adenosine Monophosphate-Activated Protein Kinase (AMPK), an enzyme that modulates glucose uptake and glycolysis. PRKAG2 mutations (OMIM#602743) are responsible for structural changes of AMPK, leading to an impaired myocyte glucidic uptake, and finally causing storage cardiomyopathy. We describe the clinical and investigative findings in a family with several affected members (NM_016203.4:c.905G>A or p.(Arg302Gln), heterozygous), highlighting the various phenotypes even in the same family, and the utility of genetic testing in diagnosing PS. The particularity of this family case is represented by the fact that the index patient was diagnosed at age 16 with cardiac hypertrophy and ventricular pre-excitation while his mother, by age 42, only had Wolff−Parkinson−White syndrome, without left ventricle hypertrophy. Both the grandmother and the great-grandmother underwent pacemaker implantation at a young age because of conduction abnormalities. Making the distinction between PS and sarcomeric HCM is actionable, given the early-onset of the disease, the numerous life-threatening consequences and the high rate of conduction disorders. In patients who exhibit cardiac hypertrophy coexisting with ventricular pre-excitation, genetic screening for PRKAG2 mutations should be considered.

Identification of the pathogenic effects of missense variants causing PRKAG2 cardiomyopathy

BACKGROUND

Pathogenic missense variants in PRKAG2, the gene for the gamma 2 regulatory subunit of adenosine monophosphate-activated protein kinase (AMPK), cause severe progressive cardiac disease and sudden cardiac death, named PRKAG2 cardiomyopathy. In our previous study, we reported a E506K variant in the PRKAG2 gene that was associated with this disease. This study aimed to functionally characterize the three missense variants (E506K, E506Q, and R531G) of PRKAG2 and determine the possible effects on AMPK activity.

METHODS

The proband was clinically monitored for eight years. To investigate the functional effects of three missense variants of PRKAG2, in vitro mutagenesis experiments using HEK293 cells with wild and mutant transcripts and proteins were comparatively analyzed using quantitative RT-PCR, immunofluorescence staining, and enzyme-linked immunosorbent assay.

RESULTS

In the long-term follow-up, the proband was deceased due to progressive heart failure. In the in vitro experimental studies, PRKAG2 was overexpressed after 48 h of transfection in three mutated cells, after which the expression levels of PRKAG2 were regressed to the level of wild-type cells in 3-weeks stably transformed cells, except for the cells with E506K variant. E506K, E506Q, and R531G variants had caused a reduction in the AMPK activity and resulted in the formation of cytoplasmic glycogen deposits.

CONCLUSION

Three missense variants that alter AMPK activity affect a residue in the CBS4 domain associated with ATP/AMP-binding. Detailed information on the influence of PRKAG2 pathogenic variants on AMPK activity would be helpful to improve the treatment and management of patients with metabolic cardiomyopathy.

Case Report: Two New Cases of Autosomal-Recessive Hypertrophic Cardiomyopathy Associated With TRIM63-Compound Heterozygous Variant

Hypertrophic cardiomyopathy (HCM) is one of the most common hereditary diseases, and it is associated with fatal complications. The clinical heterogeneity of HCM requires risk prediction models to identify patients at a high risk of adverse events. Most HCM cases are caused by mutations in genes encoding sarcomere proteins. However, HCM is associated with rare genetic variants with limited data about its clinical course and prognosis, and existing risk prediction models are not validated for such patients' cohorts. TRIM63 is one of the rare genes recently described as a cause of HCM with autosomal-recessive inheritance. Herein, we present two cases of HCM associated with TRIM63-compound heterozygous variants in young male sportsmen. They demonstrated progressively marked hypertrophy, advanced diastolic dysfunction, a significant degree of fibrosis detected by magnetic resonance imaging, and clear indications for implantable cardioverter-defibrillator. One of the cases includes the first description of TRIM63-HCM with extreme hypertrophy. The presented cases are discussed in light of molecular consequences that might underlie cardiac and muscle phenotype in patients with mutations of TRIM63, the master regulator of striated muscle mass.

Atrial Lesions in a Pedigree With PRKAG2 Cardiomyopathy: Involvement of Disrupted AMP-Activated Protein Kinase Signaling

PRKAG2 cardiomyopathy is a rare progressive disease characterized by increased ventricular wall thickness and preexcitation. Dysfunction of the protein 5′-AMP-activated protein kinase (AMPK) plays a decisive role in the progression of ventricular lesions. Although patients with the PRKAG2-R302Q mutation have a high incidence of atrial fibrillation (AF), the molecular mechanism contributing to the disease remains unclear. We carried out whole-genome sequencing with linkage analysis in three affected members of a family. Atrial samples were obtained from the proband via surgical intervention. Control atrium biopsies were obtained from patients with persistent AF. Pathological changes were analyzed using the hematoxylin and eosin (H&E), Masson, and periodic acid–Schiff (PAS) staining. The AMPK signaling pathway was investigated by western blot. A murine atrial cardiomyocyte cell line (HL-1) and human induced pluripotent stem derived atrial cardiomyocytes (hiPSC-ACMs) were transfected with an adenovirus carrying the same mutation. We used enzyme linked immunosorbent assay (ELISA) to determine the AMPK activity in HL-1 cells and hiPSC-ACMs overexpressing PRKAG2-R302Q. Pathological results showed a large quantity of glycogen accumulation and vacuolization in cardiomyocytes from the proband atrial tissue. Western blot analysis revealed that the AMPK activity was significantly downregulated compared with that of the controls. Furthermore, remarkable glycogen deposition and impairment of AMPK activity were reproduced in HL-1 cells overexpressing PRKAG2-R302Q. Taken together, PRKAG2-R302Q mutation directly impair atrial cardiomyocytes. PRKAG2-R302Q mutation lead to glycogen deposition and promote the growth of atrial lesions by disrupting the AMPK pathway.

The Value of Cardiac Magnetic Resonance Imaging in Identification of Rare Diseases Mimicking Hypertrophic Cardiomyopathy

Background: The cardiac Magnetic Resonance Imaging (MRI) characteristics of rare diseases with the hypertrophic cardiomyopathy (HCM) phenotype are not well defined. Methods: Seventy-three sequential patients and 34 of their relatives, who have the HCM phenotype, were included. All subjects underwent cardiac MRI and genetic testing. Results: Of these 107 patients with phenotypic HCM, seven rare diseases were identified: four cases with LAMP2, one case with PRKAG2, one case with TTR mutation, and one case with senile systemic amyloidosis. Subjects with rare diseases had diffuse LGE, and the percentage of those with LGE was significantly higher than that of other HCM (median: 18.9%, interquartile range (IQR): 14.05 to 28.2% versus 7.8%, IQR: 4.41 to 14.56%; p = 0.003). Additionally, global T1 and ECV were significantly higher in subjects with rare diseases (global T1: 1423.1 ± 93.3 ms versus 1296.2 ± 66.6 ms; global ECV: 44.3 ± 11.5% versus 29.9 ± 4.5%; all p < 0.001). Conclusions: Cardiac MRI suggests the existence of distinct imaging characteristics, including via LGE and T1 mapping, among rare diseases that mimic HCM and HCM itself.

Utility of Cardiac Magnetic Resonance Imaging in the Diagnosis, Prognosis, and Treatment of Infiltrative Cardiomyopathies

PURPOSE OF REVIEW

Diagnosis of infiltrative cardiomyopathies can be challenging despite differences in clinical manifestations due to overlapping cardiac manifestations. We review the salient findings by cardiac magnetic resonance imaging that aids in diagnosis, as well the potential implications for prognosis and treatment.

RECENT FINDINGS

Cardiac magnetic resonance imaging has added substantially to our understanding of various infiltrative cardiomyopathies, and the addition of late gadolinium enhancement imaging and parametric mapping has yielded additional insights regarding potential diagnoses, prognosis, and therapy. Cardiac magnetic resonance imaging should be employed in the setting of suspected hypertrophic or infiltrative cardiomyopathies to aid in diagnosis. In the setting of cardiac amyloidosis and Fabry disease, there is data to suggest that cardiac magnetic resonance imaging is useful for risk stratification as well as for monitoring response to therapy.