PRDM16 Deletion Is Associated With Sex-dependent Cardiomyopathy and Cardiac Mortality: A Translational, Multi-Institutional Cohort Study

A case report of adolescent myofibrillar myopathy due to a de novo R406W pathogenic variant in desmin with symptoms of "hypertrophic cardiomyopathy"

Objective

Myofibrillar myopathies (MFM) are a group of sporadic and inherited progressive skeletal muscle disorders that can lead to physical disability and premature death. To date, pathogenic variants in different genes are associated with MFM. MFM induced by variants in the Desmin (DES) gene is the most common subtype of MFM.

Case presentation

A 15-year-old boy with MFM was described, whose symptoms first presented as cardiac symptoms. Enlarged right and left atria, thickened ventricular septal (IVS) and mild mitral (MR) and tricuspid regurgitation (TR) in the echocardiography were found. Atrial fibrillation, intermittent atrioventricular (AV) block, ST-T changes in the dynamic electrocardiogram (ECG) were shown. Mild myopathic changes in the electromyographic exam were detected. Ultrastructural analysis found slight Z-line changes and a few small myolysis lesions, but no abnormal inclusion bodies. Genetic testing detected a heterozygous missense variant (c.1216C > T) of DES, and 2 rare variants: TNNI3K (c.1102C > G) and PRDM16 (c.3074G > A). The patient's parents didn't show skeletal and cardiac muscle disorders. DNA sequencing analysis showed no variant of DES was carried by them. Thus, we detected a case of MFM caused by de novo DES variant c.1216C > T/p.Arg406Trp with predominantly myocardial alterations.

The Trouble with Trabeculation: How Genetics Can Help to Unravel a Complex and Controversial Phenotype

Excessive trabeculation of the cardiac left ventricular wall is a complex phenotypic substrate associated with various physiological and pathological processes. There has been considerable conjecture as to whether hypertrabeculation contributes to disease and whether left ventricular non-compaction (LVNC) cardiomyopathy is a distinct pathology. Building on recent insights into the genetic basis of LVNC cardiomyopathy, in particular three meta-analysis studies exploring genotype-phenotype associations using different methodologies, this review examines how genetic research can advance our understanding of trabeculation. Three groups of genes implicated in LVNC are described-those associated with other cardiomyopathies, other cardiac/syndromic conditions and putatively with isolated LVNC cardiomyopathy-demonstrating how these findings can inform the underlying pathologies in LVNC patients and aid differential diagnosis and management in clinical practice despite the limited utility suggested for LVNC genetic testing in recent guidelines. The outstanding questions and future research priorities for exploring the genetics of hypertrabeculation are discussed.

Nonsense Variant PRDM16-Q187X Causes Impaired Myocardial Development and TGF-β Signaling Resulting in Noncompaction Cardiomyopathy in Humans and Mice

BACKGROUND

PRDM16 plays a role in myocardial development through TGF-β (transforming growth factor-beta) signaling. Recent evidence suggests that loss of PRDM16 expression is associated with cardiomyopathy development in mice, although its role in human cardiomyopathy development is unclear. This study aims to determine the impact of PRDM16 loss-of-function variants on cardiomyopathy in humans.

METHODS

Individuals with PRDM16 variants were identified and consented. Induced pluripotent stem cell-derived cardiomyocytes were generated from a proband hosting a Q187X nonsense variant as an in vitro model and underwent proliferative and transcriptional analyses. CRISPR (clustered regularly interspaced short palindromic repeats)-mediated knock-in mouse model hosting the Prdm16Q187X allele was generated and subjected to ECG, histological, and transcriptional analysis.

RESULTS

We report 2 probands with loss-of-function PRDM16 variants and pediatric left ventricular noncompaction cardiomyopathy. One proband hosts a PRDM16-Q187X variant with left ventricular noncompaction cardiomyopathy and demonstrated infant-onset heart failure, which was selected for further study. Induced pluripotent stem cell-derived cardiomyocytes prepared from the PRDM16-Q187X proband demonstrated a statistically significant impairment in myocyte proliferation and increased apoptosis associated with transcriptional dysregulation of genes implicated in cardiac maturation, including TGF-β-associated transcripts. Homozygous Prdm16Q187X/Q187X mice demonstrated an underdeveloped compact myocardium and were embryonically lethal. Heterozygous Prdm16Q187X/WT mice demonstrated significantly smaller ventricular dimensions, heightened fibrosis, and age-dependent loss of TGF-β expression. Mechanistic studies were undertaken in H9c2 cardiomyoblasts to show that PRDM16 binds TGFB3 promoter and represses its transcription.

CONCLUSIONS

Novel loss-of-function PRDM16 variant impairs myocardial development resulting in noncompaction cardiomyopathy in humans and mice associated with altered TGF-β signaling.