# Prenatal diagnosis of recurrent hypoplastic left heart syndrome associated with MYH6 variants: a case report

B Najib, T Quibel, A Tessier, J Mortreux, P Bouvagnet, C Cohen, François

Vialard, R Dard

► To cite this version:

B Najib, T Quibel, A Tessier, J Mortreux, P Bouvagnet, et al. Prenatal diagnosis of recurrent hypoplastic left heart syndrome associated with MYH6 variants: a case report. BMC Cardiovascular Disorders, 2023, 23, 10.1186/s12872-023-03169-z. http://hal.inrae.fr/hal-04056066

HAL Id: hal-04056066

https://hal.inrae.fr/hal-04056066

Submitted on 3 Apr 2023

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
CASE REPORT

Open Access

<figure><img src="image_2.png" /></figure>

# Prenatal diagnosis of recurrent hypoplastic left heart syndrome associated with *MYH6* variants: a case report

B. Najib<fnref n="1" />,<fnref n="2" />, T. Quibel<fnref n="2" />, A. Tessier<fnref n="3" />, J. Mortreux<fnref n="4" />, P. Bouvagnet<fnref n="4" />, C. Cohen<fnref n="3" />, F. Vialard<fnref n="3" />,<fnref n="5" /> and R. Dard<fnref n="3" />,<fnref n="5" />*

**Abstract**

**Background** Hypoplastic left heart syndrome (HLHS) is a rare but genetically complex and clinically and anatomically severe form of congenital heart disease (CHD).

**Case presentation** Here, we report on the use of rapid prenatal whole-exome sequencing for the prenatal diagnosis of a severe case of neonatal recurrent HLHS caused by heterozygous compound variants in the *MYH6* gene inherited from the (healthy) parents. *MYH6* is known to be highly polymorphic; a large number of rare and common variants have variable effects on protein levels. We postulated that two hypomorphic variants led to severe CHD when associated in trans; this was consistent with the autosomal recessive pattern of inheritance. In the literature, dominant transmission of *MYH6*-related CHD is more frequent and is probably linked to synergistic heterozygosity or the specific combination of a single, pathogenic variant with common *MYH6* variants.

**Conclusions** The present report illustrates the major contribution of whole-exome sequencing (WES) in the characterization of an unusually recurrent fetal disorder and considered the role of WES in the prenatal diagnosis of disorders that do not usually have a genetic etiology.

**Keywords** Hypoplastic left heart syndrome, *MYH6*, *MYH7*, Congenital heart disease, Case report

**Background**

The first-trimester prenatal diagnosis of congenital heart disease (CHD) using transvaginal ultrasound was first reported in 1990s [1]. Since then, various groups with

a high risk of CHD have been defined: these include increased nuchal translucency in the fetus, certain maternal illnesses (e.g., diabetes mellitus), conception via assisted reproductive technology, exposure to teratogenic drugs, an unambiguous family history and/or previous pregnancies with CHD [2]. In the fetal echocardiogram, the ventricles should be symmetric and equivalent in volume; any differences in size are suggestive of disease [3]. However, first-trimester fetal cardiac ultrasound has a limited ability to diagnosing subtle, minor, late-onset or progressive fetal pathologies such as ventricular septal defects, cardiac tumors, valvular stenosis or regurgitation, and coarctation of the aorta [4].

Hypoplastic left heart syndrome (HLHS) is a clinically and anatomically severe form of CHD [5]. It accounts for around 4% of cases of CHD but is responsible for 15–25% of the associated deaths [6]. HLHS combines atresia or

<footnote>*Correspondence:</footnote>

<footnote>R. Dard
Rodolphe.Dard@ght-yvelinesnord.fr</footnote>

<footnote n="1">¹ Department of Obstetrics and Gynecology, Saint Joseph University,
Beirut 0000, Lebanon</footnote>

<footnote n="2">² Department of Obstetrics and Antenatal Fetal Medicine, Centre
Hospitalier Intercommunal de Poissy-Saint-Germain-en-Laye,
78300 Poissy, France</footnote>

<footnote n="3">³ Department of Genetics, Centre Hospitalier Intercommunal de Poissy-Saint-Germain-en-Laye, 78300 Poissy, France</footnote>

<footnote n="4">⁴ Service de Génétique, Laboratoire Eurofins Biomnis, 69007 Lyon, France</footnote>

<footnote n="5">⁵ RHUMA, UMR-BREED, INRA-ENVA-UVSQ, 78180 Montigny Le Bretonneux,
France</footnote>
stenosis of the aortic or mitral valves with hypoplasia of
the left ventricle and the ascending aorta [7].

Although the cause of HLHS is unknown, severe car-
diomyopathy is thought to be a complex genetic disor-
der [7]; the genetic analysis of families with inherited left
heart abnormalities (including HLHS, a bicuspid aortic
valve, and coarctation of the aorta) have identified a few
genes in which mutations are likely to be causative (nota-
bly *NKX2.5* [8], *NOTCH1* [9–11] and *MYH6* [5, 12, 13]).

The present report highlights the use of rapid prena-
tal whole-exome sequencing (WES) to diagnose a severe
case of recurrent, neonatal HLHS (cause by compound
heterozygous *MYH6* variants) early in pregnancy. Writ-
ten informed consent was obtained from the patient for
publication of this case report and any accompanying
images.

Case presentation

We report on the case of a 40-year-old, nonsmoking,
nulliparous, Caucasian woman (BMI: 31 kg/m²) with
an unremarkable medical history other than idiopathic
hypertension (treated with labetalol 200 mg once daily).
After spontaneous conception, the woman was referred
to our center in April 2020 for an undefined fetal cardi-
opathy. The results of the first-trimester ultrasound scan
were normal (crown rump length: 63.68 mm; nuchal
translucency: 1.7 mm), with a low risk of trisomy 21 (1
in 1548; PAPP-A: 0.65 multiples of the median, β-HCG:
0.59 multiples of the median) and a negative, non-inva-
sive prenatal test requested by the woman. The diagnosis
of severe HLHS with mitral and aortic stenosis was made
at 23 weeks of gestation (w.g.) (Fig. 1). The results of a
chromosomal microarray (CMA) analysis of an amniotic
fluid sample were normal. The couple requested termina-
tion of pregnancy at 25 w.g.; given the severe prognosis,

the request was approved by the multidisciplinary ante-
natal board. The couple did not allow a fetal autopsy to be
performed.

The parents had normal cardiac ultrasound findings
and did not report a family history of CHD or adult car-
diomyopathy. The parents were reassured by the initial
genetic counselling because HLHS is usually sporadic; in
the absence of a family history, the risk of recurrence is
2–4% [14].

A year later (in April 2021, after 13 w.g.), the women was referred for an early morphological ultrasound check-up on her next pregnancy, which revealed cardiac asymmetry and aortic stenosis (Figs. 2 and 3). The diagnosis of HLHS was confirmed at 15 w.g. Again, the results of a CMA analysis of an amniotic fluid sample were normal.

In view of the recurrence of HLHS, we suggested WES.
The couple agreed, and a quartet analysis was performed
on fetal DNA stored from the previous pregnancy, DNA
from the ongoing pregnancy, and the parents' DNA.
WES revealed that both fetuses were compound het-
erozygous for probably pathogenic *MYH6* variants
(class 4, according to the American College of Medi-
cal Genetics and Genomics (ACMG) classification [15])
inherited from the mother and the father. The mother
carried *MYH6* (NM_002471.4) chr14: g.23853649A > T
c.5565+2 T > A, predicted to be a loss-of-function
(splice donor) variant that was not present in population
databases [16]. The father carried *MYH6* (NM_002471.4)
chr14:g.23857395G > T c.4328C > A p.(Ala1443Asp) – a
very rare missense variant that is predicted to be patho-
genic, according to the ACMG classification and the Var-
some database (https://varsome.com/). Furthermore, the
wild-type and mutant amino acids' respective physico-
chemical properties are very different (Grantham score:

<figure><img src="image_3.png" /><figcaption>**Fig. 1** Severe left hypoplastic heart syndrome</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>**Fig. 2** Cardiac asymmetry</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Fig. 3** Severe aortic stenosis</figcaption></figure>

126, on a 1-to-215 scale), and the alanine at position 1443 is highly conserved from *Tetraodon nigroviridis* to *Homo sapiens*. Before receiving the WES results, the severe prognosis for HLHS prompted the woman to request termination of pregnancy at 16 w.g.

**Discussion & conclusions**

Cardiac muscle myosin consist of two heavy chain subunits, two light chain subunits, and two regulatory subunits. *MYH6* codes for myosin heavy chain α (MHC-α), the major myosin isoform in the fetal heart [17]. After birth, MHC expression switches to *MYH7*, located 4 kb downstream of *MYH6* and which codes for MHC-β.

Relative to MHC-β, MHC-α has 1.5 to 3 times more contractile velocity and a 0.6-fold shorter actin attachment duration. In the adult heart, MHC-β expression is predominates in the ventricles and MHC-α expression predominates in the atria.

Pathogenic *MYH6* variants have been described in several cardiac diseases. For example, it has been shown that heterozygous variants are responsible for moderately severe types of CHD, such as atrial septal defects and AVSD [18] whereas homozygous or compound heterozygous variants are responsible for severe CHD such as HLHS [19]. *MYH6* is also thought to be involved in adult familial hypertrophic cardiomyopathy. The association
between *MYH6* variants and HLHS has already been reported; in a study of 190 unrelated HLHS subjects, rare *MYH6* variants were observed in around 10% of cases [5]. More recently, whole-genome sequencing revealed a highly significant (p=0.000068), abnormally high proportion of pathogenic *MYH6* variants observed in 197 patients with HLHS (vs. 813 controls) [13]. The frequency of *MYH6* variants was also 10% in this population of patients with HLHS. Despite the presence of autosomal dominant transmission of left heart disease/cardioomyopathy in some families, a single pathogenic *MYH6* variant alone might not be enough to cause disease: a second hit might be necessary. Interestingly, the second hit might be either a second rare *MYH6* pathogenic variant (i.e. compound heterozygosity), a “common” *MYH6* variant (minor allele frequency > 0.01) or a variant in a modifier gene like *FLNC* (i.e. synergistic heterozygosity). These various possibilities might explain the broad phenotypic spectrum associated with *MYH6* variants (Fig. 4), which ranges from a normal heart to a severe form of

CHD like HLHS. As reported for many genes with a high variant density, mutations in *MYH6* and *CFTR* are probably associated with a broad spectrum of effects and marked phenotypic variability.

Discordant inheritance patterns have been reported in the literature. The versatile nature of MYH6-related inheritance prompts us to think that MYH6 is at the interface between Mendelian autosomal-dominant inheritance and autosomal-recessive inheritance and thus has an unconventional pattern of inheritance.

The “common variant hypothesis” has been further underpinned by several recent reports of an association between rare variants and common variants in MYH6-related conditions [20] and for other genes responsible for congenital left heart defects [21]. This hypothesis is also supported by the results of several genome-wide association studies [22–24], in which MYH6 polymorphisms were linked to cardiac disease in the general population; hence, a common variant might have harmful consequences. In the overall genetic landscape and

<figure><img src="image_6.png" /><figcaption>**Fig. 4** The genotype–phenotype relationship for *MYH6* in the “second variant” hypothesis. mutations in *MYH6* is responsible for degenerative heart diseases or cardiac malformations of varying severity. Three main genotypes are thought to be responsible for these diseases: (i) classical autosomal-recessive inheritance of two rare, pathogenic *MYH6* variants, responsible for the most severe phenotype; (ii) synergistic heterozygosity, i.e. the combination of a single pathogenic *MYH6* variant with a modifier variant in an interacting gene (*FLNC* in this case), and (iii) variable compound heterozygosity, i.e. the combination of a single *MYH6* pathogenic variant with one or more common *MYH6* variants, with intrafamily variability. ASD: atrial septal defect, AV: aortic valve, Coarc: coarctation, FLNC: filamin C, HCM: hypertrophic cardiomyopathy, HLHS: hypoplastic left heart syndrome</figcaption></figure>
along with environmental factors and modifier genes, the “common variant hypothesis” tends to explain incomplete penetrance and the variable expressivity of Mendelian autosomal-dominant diseases [25].

Cases of compound heterozygosity or homozygosity for *MYH6* mutations are rare; to the best of our knowledge, the only literature report concerned cases in four families [18]. Most of these cases could have been due to synergistic heterozygosity or an association with a common *MYH6* variant. It should be noted that *MYH6* is one of the most variable genes, and so there are probably many common alleles. In the case described here, neither the fetus nor the parents carried a “common” *MYH6* or *FLNC* variant; this is consistent with the absence of a family history of CHD and hypertrophic cardiomyopathy and the classical autosomal recessive transmission of HLHS.

Moreover, the presence of *MYH6* variants is associated with greater expression of *MYH7*, which results in hypocontractility [5]. According to the literature, CHD is associated with low levels of *MYH6* mRNA and higher levels of *MYH7* mRNA [26].

There are two possible explanations for a disease-causing effect of *MYH6* variants. Firstly, severe valvular stenosis might led to ventricular dysmorphology and reduced preload [7]. Secondly, the defective expansion and/or differentiation of cardiomyocytes might result in ventricular dysmorphology and dysfunction [27]. In the present case, we observed left hypoplastic heart failure with mitral and aortic stenosis; these observations are compatible with the first hypothesis. The presence of *MYH6* variants is strongly associated with *MYH7* over-expression in both atrial and ventricular tissues [5], leading to hypocontractility. Delayed fetal blood flow from the right atrium to the left atrium and through the mitral valve would then result in limited filling of the left ventricle and thus HLHS.

The present report is the first to have described the detection of *MYH6* variants related to fetal HLHS during an ongoing pregnancy. Our case also emphasizes the value of WES for understanding the unusual recurrence of fetal anomalies during pregnancy. Fetal anomalies are detected in 3% of all pregnancies and are responsible for 20% of prenatal deaths [28]. Thus, some cases with an abnormal obstetric history and/or ultrasound anomalies but normal karyotyping and CMA results have been underdiagnosed [29]. WES improves the reliability of prenatal diagnosis and facilitates genetic counseling and medical decisions during early pregnancy [30]. Furthermore, WES improves the diagnostic yield for recurrent fetal structural anomalies and can reveal new genes that are potentially relevant in human development [31]. The present report illustrates

the major contribution of WES in the characterization of an unusually recurrent fetal disorder and considered the role of WES in the prenatal diagnosis of disorders that do not usually have a genetic etiology. A better understanding of genetic mechanisms and WES results is crucial for future medical practice.

**Abbreviations**

HLHS Hypoplastic left heart syndrome

CHD Congenital heart disease

WES Whole-exome sequencing

ACMG American College of Medical Genetics and Genomics

**Acknowledgements**

Not applicable.

**Authors' contributions**

BN: Project development, Manuscript writing. TQ: Manuscript editing. AT: Genetic analysis. JM: Genetic analysis. PB: Genetic analysis. CC: Genetic analysis. FV Protocol development, Manuscript editing. RD: Protocol development, Manuscript editing. All authors have read and approved the manuscript.

**Funding**

No funding source to declare.

**Availability of data and materials**

Upon request by contact to the corresponding author Rodolphe.dard@gmail.com.

**Declarations**

**Ethics approval and consent to participate**

Not applicable.

**Consent for publication**

Written informed consent for publication of their clinical details and/or clinical images was obtained from the patient.

**Competing interests**

The authors declare that they have no competing interests.

Received: 8 July 2022 Accepted: 2 March 2023

Published online: 08 March 2023

**References**

1. McBrien A, Hornberger LK. Early fetal echocardiography. Birth Defects Res. 2019;111(8):370-9.

2. Donofrio MT, Moon-Grady AJ, Hornberger LK, Copel JA, Sklansky MS, Abuhamad A, et al. Diagnosis and treatment of fetal cardiac disease: a scientific statement from the American Heart Association. Circulation. 2014;129(21):2183-242.

3. Smrcek JM, Berg C, Geipel A, Fimmers R, Diedrich K, Gembruch U. Early fetal echocardiography: heart biometry and visualization of cardiac structures between 10 and 15 weeks' gestation. J Ultrasound Med Off J Am Inst Ultrasound Med. 2006;25(2):173-82 (quiz 183-5).

4. Zidere V, Bellsham-Revell H, Persico N, Allan LD. Comparison of echocardiographic findings in fetuses at less than 15 weeks' gestation with later cardiac evaluation. Ultrasound Obstet Gynecol. 2013;42(6):679-86.

5. Tomita-Mitchell A, Stamm KD, Mahnke DK, Kim MS, Hidestrand PM, Liang HL, et al. Impact of MYH6 variants in hypoplastic left heart syndrome. Physiol Genomics. 2016;48(12):912-21.
6. Boneva RS, Botto LD, Moore CA, Yang Q, Correa A, Erickson JD. Mortality associated with congenital heart defects in the United States: trends and racial disparities, 1979–1997. Circulation. 2001;103(19):2376–81.

7. Hinton RB, Martin LJ, Tabangin ME, Mazwi ML, Cripe LH, Benson DW. Hypoplastic left heart syndrome is heritable. J Am Coll Cardiol. 2007;50(16):1590–5.

8. Elliott DA, Kirk EP, Yeoh T, Chandar S, McKenzie F, Taylor P, et al. Cardiac homeobox gene NKX2-5 mutations and congenital heart disease: associations with atrial septal defect and hypoplastic left heart syndrome. J Am Coll Cardiol. 2003;41(11):2072–6.

9. Mutations in NOTCH1 cause aortic valve disease | Nature. Available from: https://www.nature.com/articles/nature03940. cited 2021 Dec 18

10. McBride KL, Riley MF, Zender GA, Fitzgerald-Butt SM, Towbin JA, Belmont JW, et al. NOTCH1 mutations in individuals with left ventricular outflow tract malformations reduce ligand-induced signaling. Hum Mol Genet. 2008;17(18):2886–93.

11. Hrstka SCL, Li X, Nelson TJ, Wanek Program Genetics Pipeline Group. NOTCH1-Dependent Nitric Oxide Signaling Deficiency in Hypoplastic Left Heart Syndrome Revealed Through Patient-Specific Phenotypes Detected in Bioengineered Cardiogenesis. Stem Cells Dayt Ohio. 2017;35(4):1106–19.

12. Theis JL, Zimmermann MT, Evans JM, Eckloff BW, Wieben ED, Qureshi MY, et al. Recessive MYH6 Mutations in Hypoplastic Left Heart With Reduced Ejection Fraction. Circ Cardiovasc Genet. 2015;8(4):564–71.

13. Theis JL, Hu JJ, Sundsbak RS, Evans JM, Bamlet WR, Qureshi MY, et al. Genetic Association Between Hypoplastic Left Heart Syndrome and Cardiomyopathies. Circ Genomic Precis Med. 2021;14(1):e003126.

14. Hypoplastic left heart syndrome | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. Available from: https://rarediseases.info.nih.gov/diseases/6739/hypoplastic-left-heart-syndrome/cases/38923. cited 2022 Apr 23

15. Richards S, Aziz N, Bale S, Bick D, Das S, Gastier-Foster J, et al. Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Genet Med. 2015;17(5):405–23.

16. gnomAD. Available from: https://gnomad.broadinstitute.org/. cited 2022 Mar 3

17. Hao E, Zhang G, Mu L, Ma N, Wang T. Establishment of a human MYH6 compound heterozygous knockout hESC line to model cardiomyopathy and congenital heart defects by CRISPR/Cas9 system. Stem Cell Res. 2020;16(50):102128.

18. Posch MG, Waldmuller S, Müller M, Scheffold T, Fournier D, Andrade-Navarro MA, et al. Cardiac Alpha-Myosin (MYH6) Is the Predominant Sarcomeric Disease Gene for Familial Atrial Septal Defects. PLoS ONE. 2011;6(12):e28872.

19. Liu H, Giguet-Valard AG, Simonet T, Szenker-Ravi E, Lambert L, Vincent-Delorme C, et al. Next-generation sequencing in a series of 80 fetuses with complex cardiac malformations and/or heterotaxy. Hum Mutat. 2020;41(12):2167–78.

20. Anfinson M, Fitts RH, Lough JW, James JM, Simpson PM, Handler SS, et al. Significance of α-Myosin Heavy Chain (MYH6) Variants in Hypoplastic Left Heart Syndrome and Related Cardiovascular Diseases. J Cardiovasc Dev Dis. 2022;9(5):144.

21. McBride KL, Zender GA, Fitzgerald-Butt SM, Seagraves NJ, Fernbach SD, Zapata G, et al. Association of common variants in ERBB4 with congenital left ventricular outflow tract obstruction defects. Birt Defects Res A Clin Mol Teratol. 2011;91(3):162–8.

22. Eijgelsheim M, Newton-Cheh C, Sotoodehnia N, de Bakker PIW, Müller M, Morrison AC, et al. Genome-wide association analysis identifies multiple loci related to resting heart rate. Hum Mol Genet. 2010;19(19):3885–94.

23. Hindorff LA, Sethupathy P, Junkins HA, Ramos EM, Mehta JP, Collins FS, et al. Potential etiologic and functional implications of genome-wide association loci for human diseases and traits. Proc Natl Acad Sci U S A. 2009;106(23):9362–7.

24. MacArthur J, Bowler E, Cerezo M, Gil L, Hall P, Hastings E, et al. The new NHGRI-EBI Catalog of published genome-wide association studies (GWAS Catalog). Nucleic Acids Res. 2017;45(D1):D896-901.

25. Kingdom R, Wright CF. Incomplete Penetrance and Variable Expressivity: From Clinical Studies to Population Cohorts. Front Genet. 2022;13:920390.

26. Myocardial gene expression in dilated cardiomyopathy treated with beta-blocking agents | Cochrane Library. Available from: https://doi.org/10.1002/central/CN-00379876/full. cited 2021 Oct 19

27. deAlmeida A, McQuinn T, Sedmera D. Increased Ventricular Preload Is Compensated by Myocyte Proliferation in Normal and Hypoplastic Fetal Chick Left Ventricle. Circ Res. 2007;100(9):1363–70.

28. Al-Hamed MH, Kurdi W, Khan R, Tulbah M, AlNemer M, AlSahan N, et al. Prenatal exome sequencing and chromosomal microarray analysis in fetal structural anomalies in a highly consanguineous population reveals a propensity of ciliopathy genes causing multisystem phenotypes. Hum Genet. 2021. Available from: https://doi.org/10.1007/s00439-021-02406-9. cited 2021 Dec 18.

29. Jelin AC, Vora N. Whole Exome Sequencing: Applications in Prenatal Genetics. Obstet Gynecol Clin North Am. 2018;45(1):69–81.

30. Jin C, Qian H, Xu T, Chen J, Li X, Gu Z. Prenatal diagnosis by whole exome sequencing in a family with a novel TBR1 mutation causing intellectual disability. Taiwan J Obstet Gynecol. 2021;60(6):1094–7.

31. Pauta M, Martinez-Portilla RJ, Borrell A. Prenatal Exome Sequencing in Recurrent Fetal Structural Anomalies: Systematic Review and Meta-Analysis. J Clin Med. 2021;10(20):4739.

## Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Ready to submit your research? Choose BMC and benefit from:

* fast, convenient online submission

* thorough peer review by experienced researchers in your field

* rapid publication on acceptance

* support for research data, including large and complex data types

* gold Open Access which fosters wider collaboration and increased citations

* maximum visibility for your research: over 100M website views per year

At BMC, research is always in progress.

Learn more biomedcentral.com/submissions

<figure><img src="image_7.png" /></figure>