Left-ventricular non-compaction (LVNC): a clinical feature more often observed in terminal deletion 1p36 than previously expected

Neonatal Non-compacted Cardiomyopathy: Predictors of Poor Outcome

Non-compacted cardiomyopathy (NCM) is a heterogenous myocardial disorder. Although much has been published in recent years, little is known about NCM in the neonatal period. The objective of this study is to characterize the involvement of newborns affected with NCM and to identify risk factors associated with increased mortality. This is a retrospective study including all neonates diagnosed with NCM between 2006 and 2018. Diagnosis was based on echocardiographic findings. Data were collected regarding prenatal history, gestational age and weight at birth, gender, age at diagnosis, left or biventricular involvement and associated malformations, medical and surgical treatments, and evolution. Fourteen patients were included. The median follow-up duration was 34 months (range 1-87 months). The left ventricular apex and lateral wall were involved in all cases (100%). Thirteen patients (92.8%) had other associated heart malformations. Six patients (42.8%) died during the follow-up period. Patients who had biventricular involvement and poor ventricular function presented a higher risk of death. The main cause of death was ventricular dysfunction (5/6 [83.3%]). During follow-up, eight patients (57.1%) underwent surgery for their cardiac malformations, without higher mortality. NCM must be included in the differential diagnosis of neonatal cardiomyopathy. The higher mortality observed in our series is related not only to the high association with congenital heart disease, but also to a greater presence of early and severe left ventricular dysfunction. We did not find that patients who underwent surgery with cardiopulmonary bypass had worse outcomes.

MIB2 variants altering NOTCH signalling result in left ventricle hypertrabeculation/non-compaction and are associated with Ménétrier-like gastropathy

We performed whole exome sequencing in individuals from a family with autosomal dominant gastropathy resembling Ménétrier disease, a premalignant gastric disorder with epithelial hyperplasia and enhanced EGFR signalling. Ménétrier disease is believed to be an acquired disorder, but its aetiology is unknown. In affected members, we found a missense p.V742G variant in MIB2, a gene regulating NOTCH signalling that has not been previously linked to human diseases. The variant segregated with the disease in the pedigree, affected a highly conserved amino acid residue, and was predicted to be deleterious although it was found with a low frequency in control individuals. The purified protein carrying the p.V742G variant showed reduced ubiquitination activity in vitro and white blood cells from affected individuals exhibited significant reductions of HES1 and NOTCH3 expression reflecting alteration of NOTCH signalling. Because mutations of MIB1, the homolog of MIB2, have been found in patients with left ventricle non-compaction (LVNC), we investigated members of our family with Ménétrier-like disease for this cardiac abnormality. Asymptomatic left ventricular hypertrabeculation, the mildest end of the LVNC spectrum, was detected in two members carrying the MIB2 variant. Finally, we identified an additional MIB2 variant (p.V984L) affecting protein stability in an unrelated isolated case with LVNC. Expression of both MIB2 variants affected NOTCH signalling, proliferation and apoptosis in primary rat cardiomyocytes.In conclusion, we report the first example of left ventricular hypertrabeculation/LVNC with germline MIB2 variants resulting in altered NOTCH signalling that might be associated with a gastropathy clinically overlapping with Ménétrier disease.

What Is New in Genetics of Congenital Heart Defects?

Epidemiological studies, clinical observations, and advances in molecular genetics are contributing to the understanding of the etiology of congenital heart defects (CHDs). Several phenotype-genotype correlation studies have suggested that specific morphogenetic mechanisms put in motion by genes can result in a specific cardiac phenotype. The use of new technologies has increased the possibility of identification of new genes and chromosomal loci in syndromic and non-syndromic CHDs. There are a number of methods available for genetic research studies of CHDs, including cytogenetic analysis, linkage and association studies, copy number variation (CNV) and DNA micro-array analysis, and whole exome sequencing. The altered dosage of contiguous genes included inside CNVs can produce new syndromic CHDs, so that several different new genomic conditions have been identified. These include duplication 22q11.2 syndrome, distal 22q11.2 deletion syndrome, deletion and duplication 1q21.1, and deletion 1p36 syndrome. Molecular techniques such as whole exome sequencing have lead to the identification of new genes for monogenic syndromes with CHD, as for example in Adams-Oliver, Noonan, and Kabuki syndrome. The variable expressivity and reduced penetrance of CHDs in genetic syndromes is likely influenced by genetic factors, and several studies have been performed showing the involvement of modifier genes. It is not easy to define precisely the genetic defects underlying non-syndromic CHDs, due to the genetic and clinical heterogeneity of these malformations. Recent experimental studies have identified multiple CNVs contributing to non-syndromic CHD. The number of identified genes for non-syndromic CHDs is at this time limited, and each of the identified genes has been shown to be implicated only in a small proportion of CHD. The application of new technologies to specific cases of CHD and pedigrees with familial recurrence and filtering genes mapping in CNV regions can probably in the future add knowledge about new genes for non-syndromic CHDs.

Microarray analysis of 50 patients reveals the critical chromosomal regions responsible for 1p36 deletion syndrome-related complications

OBJECTIVE

Monosomy 1p36 syndrome is the most commonly observed subtelomeric deletion syndrome. Patients with this syndrome typically have common clinical features, such as intellectual disability, epilepsy, and characteristic craniofacial features.

METHOD

In cooperation with academic societies, we analyzed the genomic copy number aberrations using chromosomal microarray testing. Finally, the genotype-phenotype correlation among them was examined.

RESULTS

We obtained clinical information of 86 patients who had been diagnosed with chromosomal deletions in the 1p36 region. Among them, blood samples were obtained from 50 patients (15 males and 35 females). The precise deletion regions were successfully genotyped. There were variable deletion patterns: pure terminal deletions in 38 patients (76%), including three cases of mosaicism; unbalanced translocations in seven (14%); and interstitial deletions in five (10%). Craniofacial/skeletal features, neurodevelopmental impairments, and cardiac anomalies were commonly observed in patients, with correlation to deletion sizes.

CONCLUSION

The genotype-phenotype correlation analysis narrowed the region responsible for distinctive craniofacial features and intellectual disability into 1.8-2.1 and 1.8-2.2 Mb region, respectively. Patients with deletions larger than 6.2 Mb showed no ambulation, indicating that severe neurodevelopmental prognosis may be modified by haploinsufficiencies of KCNAB2 and CHD5, located at 6.2 Mb away from the telomere. Although the genotype-phenotype correlation for the cardiac abnormalities is unclear, PRDM16, PRKCZ, and RERE may be related to this complication. Our study also revealed that female patients who acquired ambulatory ability were likely to be at risk for obesity.

Identification of critical regions and candidate genes for cardiovascular malformations and cardiomyopathy associated with deletions of chromosome 1p36

Cardiovascular malformations and cardiomyopathy are among the most common phenotypes caused by deletions of chromosome 1p36 which affect approximately 1 in 5000 newborns. Although these cardiac-related abnormalities are a significant source of morbidity and mortality associated with 1p36 deletions, most of the individual genes that contribute to these conditions have yet to be identified. In this paper, we use a combination of clinical and molecular cytogenetic data to define five critical regions for cardiovascular malformations and two critical regions for cardiomyopathy on chromosome 1p36. Positional candidate genes which may contribute to the development of cardiovascular malformations associated with 1p36 deletions include DVL1, SKI, RERE, PDPN, SPEN, CLCNKA, ECE1, HSPG2, LUZP1, and WASF2. Similarly, haploinsufficiency of PRDM16–a gene which was recently shown to be sufficient to cause the left ventricular noncompaction–SKI, PRKCZ, RERE, UBE4B and MASP2 may contribute to the development of cardiomyopathy. When treating individuals with 1p36 deletions, or providing prognostic information to their families, physicians should take into account that 1p36 deletions which overlie these cardiac critical regions may portend to cardiovascular complications. Since several of these cardiac critical regions contain more than one positional candidate gene–and large terminal and interstitial 1p36 deletions often overlap more than one cardiac critical region–it is likely that haploinsufficiency of two or more genes contributes to the cardiac phenotypes associated with many 1p36 deletions.

New Genetic Insights into Congenital Heart Disease

There has been remarkable progress in understanding the genetic basis of cardiovascular malformations. Chromosome microarray analysis has provided a new tool to understand the genetic basis of syndromic cardiovascular malformations resulting from microdeletion or microduplication of genetic material, allowing the delineation of new syndromes. Improvements in sequencing technology have led to increasingly comprehensive testing for aortopathy, cardiomyopathy, single gene syndromic disorders, and Mendelian-inherited congenital heart disease. Understanding the genetic etiology for these disorders has improved their clinical recognition and management and led to new guidelines for treatment and family-based diagnosis and surveillance. These new discoveries have also expanded our understanding of the contribution of genetic variation, susceptibility alleles, and epigenetics to isolated congenital heart disease. This review summarizes the current understanding of the genetic basis of syndromic and non-syndromic congenital heart disease and highlights new diagnostic and management recommendations.

Genetics of sudden cardiac death syndromes

PURPOSE OF REVIEW

To survey recent developments in the field of genetics encompassing discovery of new candidate genes, new diagnostic strategies, and new therapies for sudden cardiac death (SCD) syndromes.

RECENT FINDINGS

In addition to new mutations in known SCD genes, several novel genes not previously implicated in SCD causation have been found, particularly in long QT syndrome (e.g., KCNJ5, AKAP9, SNTA1), idiopathic ventricular fibrillation (e.g., DPP6, KCNJ8), dilated cardiomyopathy (e.g., NEBL), and hypertrophic cardiomyopathy (HCM; e.g., NEXN). Genetic SCD animal models have provided novel insights into the cellular mechanism and pathogenesis of nearly all the major SCD syndromes, which has led to several new drug therapies for patients with genetic arrhythmia syndromes (e.g., flecainide in catecholaminergic polymorphic ventricular tachycardia). Furthermore, genetic contributions to acquired heart diseases are increasingly being recognized. For example, a 21q21 locus is strongly associated with ventricular fibrillation after myocardial infarction. Near this locus is CXADR, a gene encoding a viral receptor implicated in myocarditis and dilated cardiomyopathy. Finally, common variants in cardiac ion channels and proteins likely contribute to common cardiac phenotypes.

SUMMARY

Major strides have been made in uncovering new genes, mechanisms, and syndromes that have significantly advanced the diagnosis and treatment of genetic SCD disorders.

Recurrent interstitial 1p36 deletions: Evidence for germline mosaicism and complex rearrangement breakpoints

Deletions of chromosome 1p36 are one of the most frequently encountered subtelomeric alterations. Clinical features of monosomy 1p36 include neurocognitive impairment, hearing loss, seizures, cardiac defects, and characteristic facial features. The majority of cases have occurred sporadically, implying that genomic instability plays a role in the prevalence of the syndrome. Here, we report two siblings with mild phenotypic features of the deletion syndrome, including developmental delay, hearing loss, and left ventricular non-compaction (LVNC). Microarray analysis using bacterial artificial chromosome and oligonucleotide microarrays indicated the deletions were identical, suggesting germline mosaicism. Parental phenotypes were normal, and analysis by fluorescence in situ hybridization (FISH) did not show mosaicism. These small interstitial deletions were not detectable by conventional subtelomeric FISH analysis. To investigate the mechanism of deletion further, the breakpoints were cloned and sequenced, demonstrating the presence of a complex rearrangement. Sequence analysis of genes in the deletion interval did not reveal any mutations on the intact homologue that may have contributed to the LVNC seen in both children. This is the first report of apparent germline mosaicism for this disorder. Thus, our findings have important implications for diagnostic approaches and for recurrence risk counseling in families with a child with monosomy 1p36. In addition, our results further refine the minimal critical region for LVNC and hearing loss.

Left ventricular non-compaction and its cardiac and neurologic implications

Left ventricular non-compaction, also known as left ventricular hypertrabeculation (LVHT), is a morphological abnormality of the left ventricular myocardium, characterised by a meshwork of myocardial strings, interlacing, and orderless in arrangement. LVHT is most frequently located in the apex and the lateral wall and may occur with or without other congenital or acquired cardiac abnormalities. LVHT is believed to be congenital in the majority of the cases but may develop during life in single cases (acquired LVHT). Congenital LVHT is believed to result from defective late-stage embryonic development of the myocardial architecture. The pathogenesis of acquired LVHT remains speculative. LVHT is most frequently found on transthoracic echocardiography and cardiac MRI but may be visualised also with other imaging techniques. In the majority of the cases, LVHT is associated with hereditary cardiac, neuromuscular, non-cardiac/non-muscle disease, or chromosomal aberrations. In the majority of the cases, LVHT is complicated by ventricular arrhythmias, systolic dysfunction, cardiac embolism, or sudden cardiac death. LVHT per se does not require a specific treatment. Only in case of complications, such as ventricular arrhythmias, cardioembolism, or systolic dysfunction, adequate therapy is indicated. Though initially assessed as poor, the prognosis of LVHT has meanwhile improved, most likely due to the increased awareness for the abnormality and the timely administration of adequate therapy.

Cardiogenetics, neurogenetics, and pathogenetics of left ventricular hypertrabeculation/noncompaction

BACKGROUND

Left ventricular hypertrabeculation (LVHT), also known as noncompaction or spongy myocardium, is a cardiac abnormality of unknown etiology and pathogenesis frequently associated with genetic cardiac and noncardiac disorders, particularly genetic neuromuscular disease. This study aimed to review the current knowledge about the genetic or pathogenetic background of LVHT.

METHODS

A literature review of all human studies dealing with the association of LVHT with genetic cardiac and noncardiac disorders, particularly neuromuscular disorders, was conducted.

RESULTS

Most frequently, LVHT is associated with mitochondrial disorders (mtDNA, nDNA mutations), Barth syndrome (G4.5, TAZ mutations), hypertrophic cardiomyopathy (MYH7, ACTC mutations), zaspopathy (ZASP/LDB3 mutations), myotonic dystrophy 1 (DMPK mutations), and dystrobrevinopathy (DTNA mutations). More rarely, LVHT is associated with mutations in the DMD, SCNA5, MYBPC3, FNLA1, PTPN11, LMNA, ZNF9, AMPD1, PMP22, TNNT2, fibrillin2, SHP2, MMACHC, LMX1B, HCCS, or NR0B1 genes. Additionally, LVHT occurs with a number of chromosomal disorders, polymorphisms, and not yet identified genes, as well in a familial context. The broad heterogeneity of LVHT's genetic background suggests that the uniform morphology of LVHT not only is attributable to embryonic noncompaction but also may result from induction of hypertrabeculation as a compensatory reaction of an impaired myocardium.

CONCLUSIONS

Most frequently, LVHT is associated with mutations in genes causing muscle or cardiac disease, or with chromosomal disorders. These associations require comprehensive cardiac, neurologic, and cytogenetic investigations.