Genetic resiliency associated with dominant lethal TPM1 mutation causing atrial septal defect with high heritability

Analysis of large-scale human genomic data has yielded unexplained mutations known to cause severe disease in healthy individuals. Here, we report the unexpected recovery of a rare dominant lethal mutation in TPM1, a sarcomeric actin-binding protein, in eight individuals with large atrial septal defect (ASD) in a five-generation pedigree. Mice with Tpm1 mutation exhibit early embryonic lethality with disrupted myofibril assembly and no heartbeat. However, patient-induced pluripotent-stem-cell-derived cardiomyocytes show normal beating with mild myofilament defect, indicating disease suppression. A variant in TLN2, another myofilament actin-binding protein, is identified as a candidate suppressor. Mouse CRISPR knock-in (KI) of both the TLN2 and TPM1 variants rescues heart beating, with near-term fetuses exhibiting large ASD. Thus, the role of TPM1 in ASD pathogenesis unfolds with suppression of its embryonic lethality by protective TLN2 variant. These findings provide evidence that genetic resiliency can arise with genetic suppression of a deleterious mutation.

Discovery of a genetic module essential for assigning left-right asymmetry in humans and ancestral vertebrates

The vertebrate left-right axis is specified during embryogenesis by a transient organ: the left-right organizer (LRO). Species including fish, amphibians, rodents and humans deploy motile cilia in the LRO to break bilateral symmetry, while reptiles, birds, even-toed mammals and cetaceans are believed to have LROs without motile cilia. We searched for genes whose loss during vertebrate evolution follows this pattern and identified five genes encoding extracellular proteins, including a putative protease with hitherto unknown functions that we named ciliated left-right organizer metallopeptide (CIROP). Here, we show that CIROP is specifically expressed in ciliated LROs. In zebrafish and Xenopus, CIROP is required solely on the left side, downstream of the leftward flow, but upstream of DAND5, the first asymmetrically expressed gene. We further ascertained 21 human patients with loss-of-function CIROP mutations presenting with recessive situs anomalies. Our findings posit the existence of an ancestral genetic module that has twice disappeared during vertebrate evolution but remains essential for distinguishing left from right in humans.

Common deletion variants causing protocadherin-α deficiency contribute to the complex genetics of BAV and left-sided congenital heart disease

Bicuspid aortic valve (BAV) with ~1%-2% prevalence is the most common congenital heart defect (CHD). It frequently results in valve disease and aorta dilation and is a major cause of adult cardiac surgery. BAV is genetically linked to rare left-heart obstructions (left ventricular outflow tract obstructions [LVOTOs]), including hypoplastic left heart syndrome (HLHS) and coarctation of the aorta (CoA). Mouse and human studies indicate LVOTO is genetically heterogeneous with a complex genetic etiology. Homozygous mutation in the Pcdha protocadherin gene cluster in mice can cause BAV, and also HLHS and other LVOTO phenotypes when accompanied by a second mutation. Here we show two common deletion copy number variants (delCNVs) within the PCDHA gene cluster are associated with LVOTO. Analysis of 1,218 white individuals with LVOTO versus 463 disease-free local control individuals yielded odds ratios (ORs) at 1.47 (95% confidence interval [CI], 1.13-1.92; p = 4.2 × 10-3) for LVOTO, 1.47 (95% CI, 1.10-1.97; p = 0.01) for BAV, 6.13 (95% CI, 2.75-13.7; p = 9.7 × 10-6) for CoA, and 1.49 (95% CI, 1.07-2.08; p = 0.019) for HLHS. Increased OR was observed for all LVOTO phenotypes in homozygous or compound heterozygous PCDHA delCNV genotype comparison versus wild type. Analysis of an independent white cohort (381 affected individuals, 1,352 control individuals) replicated the PCDHA delCNV association with LVOTO. Generalizability of these findings is suggested by similar observations in Black and Chinese individuals with LVOTO. Analysis of Pcdha mutant mice showed reduced PCDHA expression at regions of cell-cell contact in aortic smooth muscle and cushion mesenchyme, suggesting potential mechanisms for BAV pathogenesis and aortopathy. Together, these findings indicate common variants causing PCDHA deficiency play a significant role in the genetic etiology of common and rare LVOTO-CHD.

Anomalous aortic origin of coronary arteries: an alternative to the unroofing strategy

OBJECTIVES

Anomalous aortic origin of a coronary artery (AAOCA) is the second leading cause of sudden death in children and young adults. The most threatening anatomy is an interarterial and an intramural course, both probably involved in ischaemic phenomena and sudden death. The treatment of interarterial AAOCA remains controversial. Most of the published studies describe the results of the unroofing technique. Our study aims to evaluate the results of a different surgical approach.

METHODS

From 2005 to 2019, 61 patients were operated on for an interarterial AAOCA (median age 14.7 years). Forty patients had a right AAOCA, and 21 patients had a left AAOCA including 5 patients with intraseptal course. Seventy percent of patients were symptomatic. Five patients had an aborted sudden cardiac death. Two surgical techniques were used: an 'anatomical' repair for 35 patients (15 left and 22 right AAOCA) or a coronary translocation with creation of a neo-ostia in 19 patients (1 left and 18 right AAOCA). The 5 left AAOCA patients with an intra-septal course required a complete release of the coronary artery from the septum.

RESULTS

There was no early or late postoperative death. Three patients had an acute postoperative ischaemic event. Two patients required immediate angioplasty and stenting: 1 patient (7 years) with a hypoplastic right AAOCA and 1 patient (66 years) for inadequate tailoring after septal release. The third patient required an immediate surgical revision (H-2) for left AAOCA thrombosis at the level of the pericardial patch with full myocardial recovery at discharge. During follow-up, 1 patient with right AAOCA translocation and chronic chest pain required subsequent stenting and finally a coronary artery bypass grafting 2 years after initial surgery. One patient who had an asymptomatic mild right coronary stenosis 1 year after anatomical repair was successfully treated by angioplasty alone. All patients but 1 who underwent coronary translocation are totally asymptomatic. All patients with anatomical repair or septal release are free from ischaemic symptoms.

CONCLUSIONS

Anatomical repair might provide a better protective option for these patients. Unlike unroofing, it treats the entire intramural segment, relocates the ostium at the appropriate sinus level and corrects any acute take-off angle.

Double orifice and atrioventricular septal defect: dealing with the zone of apposition†

OBJECTIVES

A double orifice of the left atrioventricular valve (LAVV) associated with atrioventricular septal defects (AVSD) can significantly complicate surgical repair. This study reports our experience of AVSD repair over 3 decades, with special attention to the zone of apposition (ZoA) of the main orifice, and presents a technique of hemivalve pericardial extension in specific situations.

METHODS

We performed a retrospective study from 1987 to 2016 on 1067 patients with AVSD of whom 43 (4%) had a double orifice, plus 2 additional patients who required LAVV pericardial enlargement. Median age at repair was 1.3 years. Mean follow-up was 8.2 years (1 month-32 years).

RESULTS

Associated abnormalities of the LAVV subvalvular apparatus were found in 7 patients (5 parachute LAVV and 2 absence of LAVV subvalvular apparatus). ZoA was noted in 4 patients (9%): partially closed in 15 (35%) and completely closed in 24 (56%). Four patients required, either at first repair or secondarily, a hemivalve enlargement using a pericardial patch without closure of the ZoA. The early mortality rate was 7% (n = 3), all before 2000. Two patients had unbalanced ventricles and the third had a single papillary muscle. There were no late deaths. Six patients (14%) required 7 reoperations (3 early and 4 late reoperations) for LAVV regurgitation and/or dysfunction, of whom 4 (9%) required mechanical LAVV replacement (all before 2000). Freedom from late LAVV reoperation was 97% at 1 year, 94% at 5 years and 87% at 10, 20 and 30 years. Unbalanced ventricles (P = 0.045), subvalvular abnormalities (P = 0.0037) and grade >2 LAVV postoperative regurgitation (P = 0.017) were identified as risk factors for LAVV reoperations. Freedom from LAVV mechanical valve replacement was 95% at 1 year, 90% at 5 years and 85% at 10, 20 and 30 years. An anomalous LAVV subvalvular apparatus was identified as a risk factor for mechanical valve replacement (P = 0.010). None of the patients who underwent LAVV pericardial extension had significant LAVV regurgitation at the last follow-up examination.

CONCLUSIONS

Repair of AVSD and double orifice can be tricky. Preoperative LAVV regurgitation was not identified as an independent predictor of surgical outcome. LAVV hemivalve extension appears to be a useful and effective alternate surgical strategy when the ZoA cannot be closed.

A Membrane-Tethered Ubiquitination Pathway Regulates Hedgehog Signaling and Heart Development

The etiology of congenital heart defects (CHDs), which are among the most common human birth defects, is poorly understood because of its complex genetic architecture. Here, we show that two genes implicated in CHDs, Megf8 and Mgrn1, interact genetically and biochemically to regulate the strength of Hedgehog signaling in target cells. MEGF8, a transmembrane protein, and MGRN1, a RING superfamily E3 ligase, assemble to form a receptor-like ubiquitin ligase complex that catalyzes the ubiquitination and degradation of the Hedgehog pathway transducer Smoothened. Homozygous Megf8 and Mgrn1 mutations increased Smoothened abundance and elevated sensitivity to Hedgehog ligands. While mice heterozygous for loss-of-function Megf8 or Mgrn1 mutations were normal, double heterozygous embryos exhibited an incompletely penetrant syndrome of CHDs with heterotaxy. Thus, genetic interactions can arise from biochemical mechanisms that calibrate morphogen signaling strength, a conclusion broadly relevant for the many human diseases in which oligogenic inheritance is emerging as a mechanism for heritability.

Ascending aorta and aortic root replacement (with or without valve sparing) in early childhood: surgical strategies and long-term outcomes

OBJECTIVES

Aortic root and ascending aorta replacements (AARs) are rarely required in the paediatric population. We report here a series of AAR performed in young children using different surgical techniques.

METHODS

Between 1995 and 2017, 32 children under the age of 10 years (median age 5.4 years) underwent AAR procedures at our institution. Twenty-two (69%) had a connective tissue disease (infantile Marfan syndrome or Loeys-Dietz syndrome). We performed 11 AAR using a composite graft with a mechanical prosthesis and 21 valve-sparing procedures (10 Yacoub operations and 11 David operations). Median follow-up for operative survivors was 7.7 years (interquartile range 4.2-12.8 years).

RESULTS

The cardiac-related early mortality rate was 6%. Patient survival was 91% at both 1 and 10 years. Eleven survivors (38%), all with a status of post-valve-sparing procedure, required an aortic root reintervention with an aortic valve replacement after a median interval of 4.2 years. Interestingly, only patients with infantile Marfan syndrome tended to be associated with risk of reoperation.

CONCLUSIONS

Aortic root and AARs are safe in young children whatever the surgical procedure. Aortic valve-sparing procedures show good long-term results except in children with infantile Marfan syndrome whose ineluctable aortic annulus dilatation or aortic valve regurgitation requires reintervention after a short period.

Mitral valve replacement with a pulmonary autograft: long-term follow-up in an infant

A 7-month-old boy with a complete atrioventricular septal defect presented with severe left atrioventricular valve regurgitation 4 months after complete repair. As the valve was unsuitable for the repair and the annulus was too small to accommodate a mechanical prosthesis, the modified mitral Ross operation was performed. The long-term outcome was uneventful for 12 years. The mitral Ross procedure is an old-described technique in which classically the pulmonary autograft is encased in a prosthetic conduit preventing any growth potential. On the contrary, the modified technique used in this case shows that the long-term function can be obtained. This procedure may be a valuable option when mitral valve replacement is necessary in infants.

MMP21 is mutated in human heterotaxy and is required for normal left-right asymmetry in vertebrates

Heterotaxy results from a failure to establish normal left-right asymmetry early in embryonic development. By whole-exome sequencing, whole-genome sequencing and high-throughput cohort resequencing, we identified recessive mutations in MMP21 (encoding matrix metallopeptidase 21) in nine index cases with heterotaxy. In addition, Mmp21-mutant mice and mmp21-morphant zebrafish displayed heterotaxy and abnormal cardiac looping, respectively, suggesting a new role for extracellular matrix remodeling in the establishment of laterality in vertebrates.