Neonatal-lethal dilated cardiomyopathy due to a homozygous LMOD2 donor splice-site variant

Michaela Yuen,Christopher T Pappas,Jessika Iwanski,Jared M Churko,Carol C Gregorio,Lisa Worgan,Tony Roscioli,Sandra T Cooper,Susan Arbuckle,Ying Zhu,Himanshu Joshi,Edwin P Kirk

doi:10.1038/s41431-022-01043-8

Abstract

Dilated cardiomyopathy (DCM) is characterized by cardiac enlargement and impaired ventricular contractility leading to heart failure. A single report identified variants in leiomodin-2 (LMOD2) as a cause of neonatally-lethal DCM. Here, we describe two siblings with DCM who died shortly after birth due to heart failure. Exome sequencing identified a homozygous LMOD2 variant in both siblings, (GRCh38)chr7:g.123656237G > A; NM_207163.2:c.273 + 1G > A, ablating the donor 5′ splice-site of intron-1. Pre-mRNA splicing studies and western blot analysis on cDNA derived from proband cardiac tissue, MyoD-transduced proband skin fibroblasts and HEK293 cells transfected with LMOD2 gene constructs established variant-associated absence of canonically spliced LMOD2 mRNA and full-length LMOD2 protein. Immunostaining of proband heart tissue unveiled abnormally short actin-thin filaments. Our data are consistent with LMOD2 c.273 + 1G > A abolishing/reducing LMOD2 transcript expression by: (1) variant-associated perturbation in initiation of transcription due to ablation of the intron-1 donor; and/or (2) degradation of aberrant LMOD2 transcripts (resulting from use of alternative transcription start-sites or cryptic splice-sites) by nonsense-mediated decay. LMOD2 expression is critical for life and the absence of LMOD2 is associated with thin filament shortening and severe cardiac contractile dysfunction. This study describes the first splice-site variant in LMOD2 and confirms the role of LMOD2 variants in DCM.

Highlights

Dilated cardiomyopathy (DCM) is characterized by enlargement of the heart, with left or biventricular dilation, and normal or reduced thickness of the left ventricular wall [1], leading to impaired ventricular contractility
Lmod2 knock-out (KO) mice present with earlyonset, pre-weaning lethal DCM associated with cardiac muscle thin filament shortening [7, 8]
Homozygous or compound heterozygous variants in LMOD3, the predominant isoform expressed in skeletal muscle, are associated with severe-lethal nemaline myopathy associated with skeletal muscle thin filament shortening [9]

Summary

Introduction

Dilated cardiomyopathy (DCM) is characterized by enlargement of the heart, with left or biventricular dilation, and normal or reduced thickness of the left ventricular wall [1], leading to impaired ventricular contractility. Genes associated with DCM as the predominant phenotype include TTN (Titin, 20–25% of cases), LMNA (Lamin A/C, ~5% of cases), MYH7 (Myosin heavy chain 7, ~4% of cases), TNNT2 (Troponin T, ~2% of cases), MYBPC3 (Myosin-binding protein C, ~2% of cases), MYPN (Myopalladin, ~2% of cases), SCN5A (Sodium channel α unit, ~2% of cases), and PLN (Phospholamban, 1% of cases) [3]. Multiple DCM-associated genes encode for structural proteins of the cardiac sarcomere (e.g., TTN, MYH7, TNNT2, MYBPC3, MYPN). A homozygous nonsense variant in LMOD2 (c.1193G > A, p.Trp398*) was previously identified in one individual affected with DCM, associated with absence of LMOD2 protein, severe shortening of thin filaments in the left ventricle, and contractile force deficiency in patient myocytes [6]. Homozygous or compound heterozygous variants in LMOD3, the predominant isoform expressed in skeletal muscle, are associated with severe-lethal nemaline myopathy associated with skeletal muscle thin filament shortening [9]. A homozygous nonsense variant in the smooth muscle specific isoform-LMOD1 is linked to megacystis microcolon intestinal hypoperistalsis syndrome [10]

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