Genetic counseling for congenital heart disease - Practice resource of the national society of genetic counselors

Congenital heart disease (CHD) is an indication which spans multiple specialties across various genetic counseling practices. This practice resource aims to provide guidance on key considerations when approaching counseling for this particular indication while recognizing the rapidly changing landscape of knowledge within this domain. This resource was developed with consensus from a diverse group of certified genetic counselors utilizing literature relevant for CHD genetic counseling practice and is aimed at supporting genetic counselors who encounter this indication in their practice both pre- and postnatally.

Identification of a Novel Homozygous Multi-Exon Duplication in RYR2 Among Children With Exertion-Related Unexplained Sudden Deaths in the Amish Community

Importance

The exome molecular autopsy may elucidate a pathogenic substrate for sudden unexplained death.

Objective

To investigate the underlying cause of multiple sudden deaths in young individuals and sudden cardiac arrests that occurred in 2 large Amish families.

Design, Setting, and Participants

Two large extended Amish families with multiple sudden deaths in young individuals and sudden cardiac arrests were included in the study. A recessive inheritance pattern was suggested based on an extended family history of sudden deaths in young individuals and sudden cardiac arrests, despite unaffected parents. A family with exercise-associated sudden deaths in young individuals occurring in 4 siblings was referred for postmortem genetic testing using an exome molecular autopsy. Copy number variant (CNV) analysis was performed on exome data using PatternCNV. Chromosomal microarray validated the CNV identified. The nucleotide break points of the CNV were determined by mate-pair sequencing. Samples were collected for this study between November 2004 and June 2019.

Main Outcomes and Measures

The identification of an underlying genetic cause for sudden deaths in young individuals and sudden cardiac arrests consistent with the recessive inheritance pattern observed in the families.

Results

A homozygous duplication, involving approximately 26 000 base pairs of intergenic sequence, RYR2's 5'UTR/promoter region, and exons 1 through 4 of RYR2, was identified in all 4 siblings of a family. Multiple distantly related relatives experiencing exertion-related sudden cardiac arrest also had the identical RYR2 homozygous duplication. A second, unrelated family with multiple exertion-related sudden deaths and sudden cardiac arrests in young individuals, with the same homozygous duplication, was identified. Several living, homozygous duplication-positive symptomatic patients from both families had nondiagnostic cardiologic testing, with only occasional ventricular ectopy occurring during exercise stress tests.

Conclusions and Relevance

In this analysis, we identified a novel, highly penetrant, homozygous multiexon duplication in RYR2 among Amish youths with exertion-related sudden death and sudden cardiac arrest but without an overt phenotype that is distinct from RYR2-mediated catecholaminergic polymorphic ventricular tachycardia. Considering that no cardiac tests reliably identify at-risk individuals and given the high rate of consanguinity in Amish families, identification of unaffected heterozygous carriers may provide potentially lifesaving premarital counseling and reproductive planning.

Inherited intragenic PBX1 deletion: Expanding the phenotype

PBX1 encodes the pre-B cell leukemia homeobox transcription factor, a three amino acid loop extension (TALE) homeodomain transcription factor, which forms nuclear complexes with other TALE class homeodomain proteins that ultimately regulate target genes controlling organ patterning during embryogenesis. Heterozygous de novo pathogenic variants in PBX1 resulting in haploinsufficiency are associated with congenital anomalies of the kidneys and urinary tract, most commonly renal hypoplasia, as well as anomalies involving the external ear, branchial arch, heart, and genitalia, and they cause intellectual disability and developmental delay. Affected individuals described thus far have had de novo variants. Here, we report three related individuals with an inherited pathogenic intragenic PBX1 deletion with variable clinical features typical for this syndrome.

Sudden cardiac death in children and young adults without structural heart disease: a comprehensive review

Sudden cardiac death (SCD) is a rare clinical encounter in pediatrics, but its social impact is immense because of its unpredicted and catastrophic nature in previously healthy individuals. Unlike in adults where the primary cause of SCD is related to ischemic heart disease, the etiology is diverse in young SCD victims. Although certain structural heart diseases may be identified during autopsy in some SCD victims, autopsy-negative SCD is more common in pediatrics, which warrants the diagnosis of sudden arrhythmic death syndrome (SADS) based upon the assumption that the usual heart rhythm is abruptly replaced by lethal ventricular arrhythmia. Despite current advances in molecular genetics, the causes of more than half of SADS cases remain unanswered even after postmortem genetic testing. Moreover, the majority of these deaths occur at rest or during sleep even in the young. Recently, sudden unexpected death in epilepsy (SUDEP) has emerged as another etiology of SCD in children and adults, suggesting critical involvement of the central nervous system (CNS) in SCD. Primary cardiac disorders may not be solely responsible for SCD; abnormal CNS function may also contribute to the unexpected lethal event. In this review article, we provide an overview of the complex pathogenesis of SADS and its diverse clinical presentation in the young and postulate that SADS is, in part, induced by unfortunate miscommunication between the heart and CNS via the autonomic nervous system.

Molecular characterization of the calcium release channel deficiency syndrome

We identified a potentially novel homozygous duplication involving the promoter region and exons 1–4 of the gene encoding type 2 cardiac ryanodine receptor (RYR2) that is responsible for highly penetrant, exertion-related sudden deaths/cardiac arrests in the Amish community without an overt phenotype to suggest RYR2-mediated catecholaminergic polymorphic ventricular tachycardia (CPVT). Homozygous RYR2 duplication (RYR2-DUP) induced pluripotent stem cell cardiomyocytes (iPSC-CMs) were generated from 2 unrelated patients. There was no difference in baseline Ca²⁺ handling measurements between WT-iPSC-CM and RYR2-DUP-iPSC-CM lines. However, compared with WT-iPSC-CMs, both patient lines demonstrated a dramatic reduction in caffeine-stimulated and isoproterenol-stimulated (ISO-stimulated) Ca²⁺ transient amplitude, suggesting RyR2 loss of function. There was a greater than 50% reduction in RYR2 transcript/RyR2 protein expression in both patient iPSC-CMs compared with WT. Delayed afterdepolarization was observed in the RYR2-DUP-iPSC-CMs but not in the WT-iPSC-CMs. Compared with WT-iPSC-CMs, there was significantly elevated arrhythmic activity in the RYR2-DUP-iPSC-CMs in response to ISO. Nadolol, propranolol, and flecainide reduced erratic activity by 8.5-fold, 6.8-fold, and 2.4-fold, respectively, from ISO challenge. Unlike the gain-of-function mechanism observed in RYR2-mediated CPVT, the homozygous multiexon duplication precipitated a dramatic reduction in RYR2 transcription and RyR2 protein translation, a loss of function in calcium handling, and a calcium-induced calcium release apparatus that is insensitive to catecholamines and caffeine.

Molecular and functional characterization of the calcium release channel deficiency syndrome in patient-specific induced pluripotent stem cell-cardiomyocytes.

Dystrophic Cardiomyopathy: Complex Pathobiological Processes to Generate Clinical Phenotype

Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), and X-linked dilated cardiomyopathy (XL-DCM) consist of a unique clinical entity, the dystrophinopathies, which are due to variable mutations in the dystrophin gene. Dilated cardiomyopathy (DCM) is a common complication of dystrophinopathies, but the onset, progression, and severity of heart disease differ among these subgroups. Extensive molecular genetic studies have been conducted to assess genotype-phenotype correlation in DMD, BMD, and XL-DCM to understand the underlying mechanisms of these diseases, but the results are not always conclusive, suggesting the involvement of complex multi-layers of pathological processes that generate the final clinical phenotype. Dystrophin protein is a part of dystrophin-glycoprotein complex (DGC) that is localized in skeletal muscles, myocardium, smooth muscles, and neuronal tissues. Diversity of cardiac phenotype in dystrophinopathies suggests multiple layers of pathogenetic mechanisms in forming dystrophic cardiomyopathy. In this review article, we review the complex molecular interactions involving the pathogenesis of dystrophic cardiomyopathy, including primary gene mutations and loss of structural integrity, secondary cellular responses, and certain epigenetic and other factors that modulate gene expressions. Involvement of epigenetic gene regulation appears to lead to specific cardiac phenotypes in dystrophic hearts.

Infantile spasms is associated with deletion of the MAGI2 gene on chromosome 7q11.23-q21.11

Infantile spasms (IS) is the most severe and common form of epilepsy occurring in the first year of life. At least half of IS cases are idiopathic in origin, with others presumed to arise because of brain insult or malformation. Here, we identify a locus for IS by high-resolution mapping of 7q11.23-q21.1 interstitial deletions in patients. The breakpoints delineate a 500 kb interval within the MAGI2 gene (1.4 Mb in size) that is hemizygously disrupted in 15 of 16 participants with IS or childhood epilepsy, but remains intact in 11 of 12 participants with no seizure history. MAGI2 encodes the synaptic scaffolding protein membrane-associated guanylate kinase inverted-2 that interacts with Stargazin, a protein also associated with epilepsy in the stargazer mouse.

Serotonergic modulation of synapses in the developing gerbil lateral superior olive

The lateral superior olive (LSO) is a primary site of binaural convergence that responds selectively to changes in interaural level difference (ILD) by integrating ipsilateral excitatory and contralateral inhibitory inputs. The circuit matures during the first three postnatal weeks, undergoing several structural and functional changes that are influenced by afferent activity. Therefore modulation of synaptic activity by neuromodulators may participate in the maturation of this circuit. The present study describes robust effects of serotonin (5-HT) on LSO synaptic function. Using whole cell voltage-clamp recording from gerbil LSO neurons (postnatal days 6-13) in an in vitro slice preparation, we have identified several distinct forms of serotonergic modulation of spontaneous and evoked synaptic transmission. First, 1-2 min application of 5-HT (100 microM) activated prolonged bursts of spontaneous inhibitory postsynaptic currents (IPSCs). However, there was an age-dependent decline, such that this effect rarely was observed beyond postnatal day 8. 5-HT apparently increased the excitability of inhibitory afferents, because 5-HT-induced IPSCs were blocked by tetrodotoxin. A second effect of 5-HT was to depress rapidly and profoundly the amplitude of electrically evoked excitatory postsynaptic currents (EPSCs). In contrast, 5-HT also depressed evoked IPSCs but to a significantly lesser degree. The receptor subtypes mediating these effects were examined using specific 5-HT agonists and antagonists. A 5-HT1 agonist, 5-carboxamidotryptamine, produced EPSC depression but did not induce spontaneous IPSCs. A 5-HT2 agonist, alpha-Me-5-HT, reproduced all the observed effects of 5-HT (PSC depression as well as induction of spontaneous IPSCs), whereas a 5-HT2 antagonist, ketanserin, blocked the induction of spontaneous IPSCs. Therefore induction of spontaneous IPSCs is mediated by 5-HT2 receptors, whereas both 5-HT1 and 5-HT2 receptor types contribute to PSC depression. Serotonergic modulation of LSO synapses may have consequences for both developmental plasticity and auditory function. Serotonergic induction of IPSCs was observed primarily in young animals and thus may represent a mechanism for amplifying the activity of inhibitory synapses in LSO during a period of use-dependent plasticity in postnatal development. PSC depression, which preferentially affects excitation, is a potential mechanism for modulation of ILD tuning.

Multiple forms of facilitation produced by aversive tentacular stimuli in cerebral ganglion sensory neurons of Aplysia

Aversive tentacular stimuli can produce both nonassociative and associative modification of head-waving behavior of Aplysia. Sensory neurons (the J/K cluster SNs) in the cerebral ganglion of Aplysia constitute an afferent pathway for aversive stimuli of the anterior tentacles. We used intracellular recording to examine plasticity in these neurons, particularly side-specific or site-specific alterations, which may be involved in mediating aspects of the learning induced by tentacle shock. The results of these experiments indicate that the J/K SNs exhibit several forms of plasticity: (1) Post-tetanic potentiation (PTP); (2) heterosynaptic facilitation; (3) activity-dependent synaptic facilitation; and (4) side-specific spike broadening. Furthermore, by activating SNs directly to produce PTP and producing heterosynaptic facilitation with tentacular stimuli that were either inside or outside the receptive field of individual SNs, it was possible to dissect and analyze the differential contribution of intrinsic SN activity and heterosynaptic modulation to activity-dependent facilitation induced by behaviorally relevant stimuli. Collectively, these data raise the possibility that plasticity in primary afferent SNs may be involved in US processing during learning induced by tentacle stimulation.

Nonassociative and associative modification of head-waving produced by aversive tentacular stimuli in Aplysia

Head-waving, a spontaneously occurring exploratory and appetitive behavior of the marine mollusc Aplysia, provides an opportunity to examine mechanisms of learning expressed in a nonreflexive behavior. The present study explores nonassociative and associative forms of learned modification of head-waving produced using an aversive stimulus as reinforcement. Experiments on intact, freely behaving animals demonstrate that training with electric shock as an aversive unconditioned stimulus, delivered unilaterally to the anterior tentacles, produces a learned shift in head-waving behavior away from the side on which shock was applied. This behavioral change is a novel learned behavioral response that is influenced by the topographic location of an aversive stimulus. Furthermore, training with application of tentacle shock reinforcement, contingent upon the animal's head position, produces operant conditioning of head-waving. Thus, anterior tentacle shock is effective as an aversive reinforcer for both nonassociative and operant learning expressed in the head-waving behavior of Aplysia.