A low prevalence of MYH7/MYBPC3 mutations among familial hypertrophic cardiomyopathy patients in India

Novel MYBPC3 Mutations in Indian Population with Cardiomyopathies

Background

Mutations in Myosin Binding Protein C (MYBPC3) are one of the most frequent causes of cardiomyopathies in the world, but not much data are available in India.

Methods

We carried out targeted direct sequencing of MYBPC3 in 115 hypertrophic (HCM) and 127 dilated (DCM) cardiomyopathies against 197 ethnically matched healthy controls from India.

Results

We detected 34 single nucleotide variations in MYBPC3, of which 19 were novel. We found a splice site mutation [(IVS6+2T) T>G] and 16 missense mutations in Indian cardiomyopathies [5 in HCM; E258K, T262S, H287L, R408M, V483A: 4 in DCM; T146N, V321L, A392T, E393K and 7 in both HCM and DCM; L104M, V158M, S236G, R272C, T290A, G522E, A626V], but those were absent in 197 normal healthy controls. Interestingly, we found 7 out of 16 missense mutations (V158M, E258K, R272C, A392T, V483A, G522E, and A626V) in MYBPC3 were altering the evolutionarily conserved native amino acids, accounted for 8.7% and 6.3% in HCM and DCM, respectively. The bioinformatic tools predicted that those 7 missense mutations were pathogenic. Moreover, the co-segregation of those 7 mutations in families further confirmed their pathogenicity. Remarkably, we also identified compound mutations within the MYBPC3 gene of 6 cardiomyopathy patients (5%) with more severe disease phenotype; of which, 3 were HCM (2.6%) [(1. K244K + E258K + (IVS6+2T) T>G); (2. L104M + G522E + A626V); (3. P186P + G522E + A626V]; and 3 were DCM (2.4%) [(1. 5'UTR + A392T; 2. V158M+G522E; and 3.V158M + T262T + A626V].

Conclusion

The present comprehensive study on MYBPC3 has revealed both single and compound mutations in MYBPC3 and their association with disease in Indian Population with Cardiomyopathies. Our findings may perhaps help in initiating diagnostic strategies and eventually recognizing the targets for therapeutic interventions.

Molecular characterization of linker and loop-mediated structural modulation and hinge motion in the C4-C5 domains of cMyBPC

INTRODUCTION

The central C4 and C5 domains (C4C5) of cardiac myosin binding protein C (cMyBPC) contain a flexible interdomain linker and a cardiac-isoform specific loop. However, their importance in the functional regulation of cMyBPC has not been extensively studied.

METHODS AND RESULTS

We expressed recombinant C4C5 proteins with deleted linker and loop regions and performed biophysical experiments to determine each of their structural and dynamic roles. We show that the linker and C5 loop regions modulate the secondary structure and thermal stability of C4C5. Furthermore, we provide evidence through extended molecular dynamics simulations and principle component analyses that C4C5 can adopt a completely bent or latched conformation. The simulation trajectory and interaction network analyses reveal that the completely bent conformation of C4C5 exhibits a specific pattern of residue-level interactions. Therefore, we propose a "hinge-and-latch" mechanism where the linker allows a great degree of flexibility and bending, while the loop aids in achieving a completely bent and latched conformation. Although this may be one of many bent positions that C4C5 can adopt, we illustrate for the first time in molecular detail that this type of large scale conformational change can occur in the central domains of cMyBPC.

CONCLUSIONS

Our hinge-and-latch mechanism demonstrates that the linker and loop regions participate in dynamic modulation of cMyBPC's motion and global conformation. These structural and dynamic features may contribute to muscle isoform-specific regulation of actomyosin activity, and have potential implications regarding its ability to propagate or retract cMyBPC's regulatory N-terminal domains.

Novel Mutations in β-MYH7 Gene in Indian Patients With Dilated Cardiomyopathy

Background

Methods

Results

Conclusions

South Asian-Specific MYBPC3 Δ25bp Deletion Carriers Display Hypercontraction and Impaired Diastolic Function Under Exercise Stress

Background: A 25-base pair (25bp) intronic deletion in the MYBPC3 gene enriched in South Asians (SAs) is a risk allele for late-onset left ventricular (LV) dysfunction, hypertrophy, and heart failure (HF) with several forms of cardiomyopathy. However, the effect of this variant on exercise parameters has not been evaluated. Methods: As a pilot study, 10 asymptomatic SA carriers of the MYBPC3 Δ25bp variant (52.9 ± 2.14 years) and 10 age- and gender-matched non-carriers (NCs) (50.1 ± 2.7 years) were evaluated at baseline and under exercise stress conditions using bicycle exercise echocardiography and continuous cardiac monitoring. Results: Baseline echocardiography parameters were not different between the two groups. However, in response to exercise stress, the carriers of Δ25bp had significantly higher LV ejection fraction (%) (CI: 4.57 ± 1.93; p < 0.0001), LV outflow tract peak velocity (m/s) (CI: 0.19 ± 0.07; p < 0.0001), and higher aortic valve (AV) peak velocity (m/s) (CI: 0.103 ± 0.08; p = 0.01) in comparison to NCs, and E/A ratio, a marker of diastolic compliance, was significantly lower in Δ25bp carriers (CI: 0.107 ± 0.102; p = 0.038). Interestingly, LV end-diastolic diameter (LVIDdia) was augmented in NCs in response to stress, while it did not increase in Δ25bp carriers (CI: 0.239 ± 0.125; p = 0.0002). Further, stress-induced right ventricular systolic excursion velocity s' (m/s), as a marker of right ventricle function, increased similarly in both groups, but tricuspid annular plane systolic excursion increased more in carriers (slope: 0.008; p = 0.0001), suggesting right ventricle functional differences between the two groups. Conclusions: These data support that MYBPC3 Δ25bp is associated with LV hypercontraction under stress conditions with evidence of diastolic impairment.

Prediction and in silico validation of MYH7 gene missense variants in the Iranian population: a bioinformatics analysis based on Iranome database

Background

Identifying disease-causing genetic variants in a particular population improves the molecular diagnosis of genetic disorders. National genome databases provide valuable information on this matter. This study aimed to investigate the genomic variants of the MYH7 gene, related to the common heart disease, i.e., hereditary cardiomyopathy.

Results

MYH7 gene variants were extracted from the Iranome database and loaded into SPSS software. The filtration steps were performed based on the variant specification and with emphasis on identifying missense changes. Using predictive algorithms, different aspects of the changes such as allele frequency and functional defects were investigated. Our results showed that 41 (17.4%) coding variants were synonymous compared with 18 (7.7%) missense alterations. The missense variants were mostly observed in exons 20–40 that encode MyHC α-helical rod tail. The p.Pro211Leu, p.Arg787His, p.Val964Leu, p.Arg1277Gln, and p.Ala1603Thr were already known to be associated with inherited cardiomyopathy. Four of the missense variants, p.Asn1623Ser, p.Arg1588His, p.Phe1498Tyr, and p.Arg1129Ser, were located on MyHC α-helical rod tail and none of them was annotated on dbSNP or genomAD databases.

Conclusion

Our study showed several MYH7 variants associated with the disease in the Iranian population. The results emphasize the importance of analyzing the exons encoding MyHC α-helical rod tail. The investigation of genomic databases can be considered as a cost-effective strategy using targeted mutation detection analyses. The efficacy of this prediction method should be elucidated in further studies on patients’ cohorts.

Genetic, clinical, molecular, and pathogenic aspects of the South Asian-specific polymorphic MYBPC3Δ25bp variant

Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by ventricular enlargement, diastolic dysfunction, and increased risk for sudden cardiac death. Sarcomeric genetic defects are the predominant known cause of HCM. In particular, mutations in the myosin-binding protein C gene (MYBPC3) are associated with ~ 40% of all HCM cases in which a genetic basis has been established. A decade ago, our group reported a 25-base pair deletion in intron 32 of MYBPC3 (MYBPC3Δ25bp) that is uniquely prevalent in South Asians and is associated with autosomal dominant cardiomyopathy. Although our studies suggest that this deletion results in left ventricular dysfunction, cardiomyopathies, and heart failure, the precise mechanism by which this variant predisposes to heart disease remains unclear. Increasingly appreciated, however, is the contribution of secondary risk factors, additional mutations, and lifestyle choices in augmenting or modifying the HCM phenotype in MYBPC3Δ25bp carriers. Therefore, the goal of this review article is to summarize the current research dedicated to understanding the molecular pathophysiology of HCM in South Asians with the MYBPC3Δ25bp variant. An emphasis is to review the latest techniques currently applied to explore the MYBPC3Δ25bp pathogenesis and to provide a foundation for developing new diagnostic strategies and advances in therapeutics.

Reevaluation of the South Asian MYBPC3Δ25bp Intronic Deletion in Hypertrophic Cardiomyopathy

BACKGROUND

The common intronic deletion, MYBPC3Δ25, detected in 4% to 8% of South Asian populations, is reported to be associated with cardiomyopathy, with ≈7-fold increased risk of disease in variant carriers. Here, we examine the contribution of MYBPC3Δ25 to hypertrophic cardiomyopathy (HCM) in a large patient cohort.

METHODS

Sequence data from 2 HCM cohorts (n=5393) was analyzed to determine MYBPC3Δ25 frequency and co-occurrence of pathogenic variants in HCM genes. Case-control and haplotype analyses were performed to compare variant frequencies and assess disease association. Analyses were also undertaken to investigate the pathogenicity of a candidate variant MYBPC3 c.1224-52G>A.

RESULTS

Our data suggest that the risk of HCM, previously attributed to MYBPC3Δ25, can be explained by enrichment of a derived haplotype, MYBPC3Δ25/-52, whereby a small subset of individuals bear both MYBPC3Δ25 and a rare pathogenic variant, MYBPC3 c.1224-52G>A. The intronic MYBPC3 c.1224-52G>A variant, which is not routinely evaluated by gene panel or exome sequencing, was detected in ≈1% of our HCM cohort.

CONCLUSIONS

The MYBPC3 c.1224-52G>A variant explains the disease risk previously associated with MYBPC3Δ25 in the South Asian population and is one of the most frequent pathogenic variants in HCM in all populations; genotyping services should ensure coverage of this deep intronic mutation. Individuals carrying MYBPC3Δ25 alone are not at increased risk of HCM, and this variant should not be tested in isolation; this is important for the large majority of the 100 million individuals of South Asian ancestry who carry MYBPC3Δ25 and would previously have been declared at increased risk of HCM.

Association of Cardiomyopathy With MYBPC3 D389V and MYBPC3Δ25bpIntronic Deletion in South Asian Descendants

Importance

The genetic variant MYBPC3Δ25bp occurs in 4% of South Asian descendants, with an estimated 100 million carriers worldwide. MYBPC3 Δ25bp has been linked to cardiomyopathy and heart failure. However, the high prevalence of MYBPC3Δ25bp suggests that other stressors act in concert with MYBPC3Δ25bp.

Objective

To determine whether there are additional genetic factors that contribute to the cardiomyopathic expression of MYBPC3Δ25bp.

Design, Setting, andParticipants

South Asian individuals living in the United States were screened for MYBPC3Δ25bp, and a subgroup was clinically evaluated using electrocardiograms and echocardiograms at Loyola University, Chicago, Illinois, between January 2015 and July 2016.

Main Outcomes and Measures

Next-generation sequencing of 174 cardiovascular disease genes was applied to identify additional modifying gene mutations and correlate genotype-phenotype parameters. Cardiomyocytes derived from human-induced pluripotent stem cells were established and examined to assess the role of MYBPC3Δ25bp.

Results

In this genotype-phenotype study, individuals of South Asian descent living in the United States from both sexes (36.23% female) with a mean population age of 48.92 years (range, 18-84 years) were recruited. Genetic screening of 2401 US South Asian individuals found an MYBPC3Δ25bpcarrier frequency of 6%. A higher frequency of missense TTN variation was found in MYBPC3Δ25bp carriers compared with noncarriers, identifying distinct genetic backgrounds within the MYBPC3Δ25bp carrier group. Strikingly, 9.6% of MYBPC3Δ25bp carriers also had a novel MYBPC3 variant, D389V. Family studies documented D389V was in tandem on the same allele as MYBPC3Δ25bp, and D389V was only seen in the presence of MYBPC3Δ25bp. In contrast to MYBPC3Δ25bp, MYBPC3Δ25bp/D389V was associated with hyperdynamic left ventricular performance (mean [SEM] left ventricular ejection fraction, 66.7 [0.7%]; left ventricular fractional shortening, 36.6 [0.6%]; P < .03) and stem cell-derived cardiomyocytes exhibited cellular hypertrophy with abnormal Ca2+ transients.

Conclusions and Relevance

MYBPC3Δ25bp/D389V is associated with hyperdynamic features, which are an early finding in hypertrophic cardiomyopathy and thought to reflect an unfavorable energetic state. These findings support that a subset of MYBPC3Δ25bp carriers, those with D389V, account for the increased risk attributed to MYBPC3Δ25bp.

Genome-wide profiling of Sus scrofa circular RNAs across nine organs and three developmental stages

The spatio-temporal expression patterns of Circular RNA (circRNA) across organs and developmental stages are critical for its function and evolution analysis. However, they remain largely unclear in mammals. Here, we comprehensively analysed circRNAs in nine organs and three skeletal muscles of Guizhou miniature pig (S. scrofa), a widely used biomedical model animal. We identified 5,934 circRNAs and analysed their molecular properties, sequence conservation, spatio-temporal expression pattern, potential function, and interaction with miRNAs. S. scrofa circRNAs show modest sequence conservation with human and mouse circRNAs, are flanked by long introns, exhibit low abundance, and are expressed dynamically in a spatio-temporally specific manner. S. scrofa circRNAs show the greatest abundance and complexity in the testis. Notably, 31% of circRNAs harbour well-conserved canonical miRNA seed matches, suggesting that some circRNAs act as miRNAs sponges. We identified 149 circRNAs potentially associated with muscle growth and found that their host genes were significantly involved in muscle development, contraction, chromatin modification, cation homeostasis, and ATP hydrolysis-coupled proton transport; moreover, this set of genes was markedly enriched in genes involved in tight junctions and the calcium signalling pathway. Finally, we constructed the first public S. scrofa circRNA database, allowing researchers to query comprehensive annotation, expression, and regulatory networks of circRNAs.

Clinical outcomes associated with sarcomere mutations in hypertrophic cardiomyopathy: a meta-analysis on 7675 individuals

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disease, which goes along with increased risk for sudden cardiac death (SCD). Despite the knowledge about the different causal genes, the relationship between individual genotypes and phenotypes is incomplete.

METHODS AND RESULTS

We retrieved PubMed/Medline literatures on genotype-phenotype associations in patients with HCM and mutations in MYBPC3, MYH7, TNNT2, and TNNI3. Altogether, 51 studies with 7675 HCM patients were included in our meta-analysis. The average frequency of mutations in MYBPC3 (20%) and MYH7 (14%) was higher than TNNT2 and TNNI3 (2% each). The mean age of HCM onset for MYH7 mutation positive patients was the beginning of the fourth decade, significantly earlier than patients without sarcomeric mutations. A high male proportion was observed in TNNT2 (69%), MYBPC3 (62%) and mutation negative group (64%). Cardiac conduction disease, ventricular arrhythmia and heart transplantation (HTx) rate were higher in HCM patients with MYH7 mutations in comparison to MYBPC3 (p < 0.05). Furthermore, SCD was significantly higher in patients with sarcomeric mutations (p < 0.01).

CONCLUSION

A pooled dataset and a comprehensive genotype-phenotype analysis show that the age at disease onset of HCM patients with MYH7 is earlier and leads to a more severe phenotype than in patient without such mutations. Furthermore, patients with sarcomeric mutations are more susceptible to SCD. The present study further supports the clinical interpretation of sarcomeric mutations in HCM patients.

Prevalence and Clinical Implication of Double Mutations in Hypertrophic Cardiomyopathy

Background—

Available data suggests that double mutations in patients with hypertrophic cardiomyopathy are not rare and are associated with a more severe phenotype. Most of this data, however, is based on noncontemporary variant classification.

Methods and Results—

Clinical data of all hypertrophic cardiomyopathy patients with 2 rare genetic variants were retrospectively reviewed and compared with a group of patients with a single disease-causing variant. Furthermore, a literature search was performed for all studies with information on prevalence and outcome of patients with double mutations. Classification of genetic variants was reanalyzed according to current guidelines. In our cohort (n=1411), 9% of gene-positive patients had 2 rare variants in sarcomeric genes but only in 1 case (0.4%) were both variants classified as pathogenic. Patients with 2 rare variants had a trend toward younger age at presentation when compared with patients with a single mutation. All other clinical variables were similar. In data pooled from cohort studies in the literature, 8% of gene-positive patients were published to have double mutations. However, after reanalysis of reported variants, this prevalence diminished to 0.4%. All patients with 2 radical mutations in MYBPC3 in the literature had severe disease with death or heart transplant during the first year of life. Data on other specific genotype–phenotype correlations were scarce.

Conclusions—

Double mutations in patients with hypertrophic cardiomyopathy are much less common than previously estimated. With the exception of double radical MYBPC3 mutations, there is little data to guide clinical decision making in cases with double mutations.

Recent Advances in the Molecular Genetics of Familial Hypertrophic Cardiomyopathy in South Asian Descendants

The South Asian population, numbered at 1.8 billion, is estimated to comprise around 20% of the global population and 1% of the American population, and has one of the highest rates of cardiovascular disease. While South Asians show increased classical risk factors for developing heart failure, the role of population-specific genetic risk factors has not yet been examined for this group. Hypertrophic cardiomyopathy (HCM) is one of the major cardiac genetic disorders among South Asians, leading to contractile dysfunction, heart failure, and sudden cardiac death. This disease displays autosomal dominant inheritance, and it is associated with a large number of variants in both sarcomeric and non-sarcomeric proteins. The South Asians, a population with large ethnic diversity, potentially carries region-specific polymorphisms. There is high variability in disease penetrance and phenotypic expression of variants associated with HCM. Thus, extensive studies are required to decipher pathogenicity and the physiological mechanisms of these variants, as well as the contribution of modifier genes and environmental factors to disease phenotypes. Conducting genotype-phenotype correlation studies will lead to improved understanding of HCM and, consequently, improved treatment options for this high-risk population. The objective of this review is to report the history of cardiovascular disease and HCM in South Asians, present previously published pathogenic variants, and introduce current efforts to study HCM using induced pluripotent stem cell-derived cardiomyocytes, next-generation sequencing, and gene editing technologies. The authors ultimately hope that this review will stimulate further research, drive novel discoveries, and contribute to the development of personalized medicine with the aim of expanding therapeutic strategies for HCM.

Compound heterozygous or homozygous truncating MYBPC3 mutations cause lethal cardiomyopathy with features of noncompaction and septal defects

Familial hypertrophic cardiomyopathy (HCM) is usually caused by autosomal dominant pathogenic mutations in genes encoding sarcomeric or sarcomere-associated cardiac muscle proteins. The disease mainly affects adults, although young children with severe HCM have also been reported. We describe four unrelated neonates with lethal cardiomyopathy, and performed molecular studies to identify the genetic defect. We also present a literature overview of reported patients with compound heterozygous or homozygous pathogenic MYBPC3 mutations and describe their clinical characteristics. All four children presented with feeding difficulties, failure to thrive, and dyspnea. They died from cardiac failure before age 13 weeks. Features of left ventricular noncompaction were diagnosed in three patients. In the fourth, hypertrabeculation was not a clear feature, but could not be excluded. All of them had septal defects. Two patients were compound heterozygotes for the pathogenic c.2373dup p.(Trp792fs) and c.2827C>T p.(Arg943*) mutations, and two were homozygous for the c.2373dup and c.2827C>T mutations. All patients with biallelic truncating pathogenic mutations in MYBPC3 reported so far (n=21) were diagnosed with severe cardiomyopathy and/or died within the first few months of life. In 62% (13/21), septal defects or a patent ductus arteriosus accompanied cardiomyopathy. In contrast to heterozygous pathogenic mutations, homozygous or compound heterozygous truncating pathogenic MYBPC3 mutations cause severe neonatal cardiomyopathy with features of left ventricular noncompaction and septal defects in approximately 60% of patients.

The novel mitochondrial 16S rRNA 2336T>C mutation is associated with hypertrophic cardiomyopathy

Background

Hypertrophic cardiomyopathy (HCM) is a primary disorder characterised by asymmetric thickening of septum and left ventricular wall, with a prevalence of 0.2% in the general population.

Objective

To describe a novel mitochondrial DNA mutation and its association with the pathogenesis of HCM.

Methods and results

All maternal members of a Chinese family with maternally transmitted HCM exhibited variable severity and age at onset, and were implanted permanent pacemakers due to complete atrioventricular block (AVB). Nuclear gene screening (MYH7, MYBPC3, TNNT2 and TNNI3) was performed, and no potential pathogenic mutation was identified. Mitochondrial DNA sequencing analysis identified a novel homoplasmic 16S rRNA 2336T>C mutation. This mutation was exclusively present in maternal members and absent in non-maternal members. Conservation index by comparison to 16 other vertebrates was 94.1%. This mutation disturbs the 2336U-A2438 base pair in the stem–loop structure of 16S rRNA domain III, which is involved in the assembly of mitochondrial ribosome. Oxygen consumption rate of the lymphoblastoid cells carrying 2336T>C mutation had decreased by 37% compared with controls. A reduction in mitochondrial ATP synthesis and an increase in reactive oxidative species production were also observed. Electron microscopic analysis indicated elongated mitochondria and abnormal mitochondrial cristae shape in mutant cells.

Conclusions

It is suggested that the 2336T>C mutation is one of pathogenic mutations of HCM. This is the first report of mitochondrial 16S rRNA 2336T>C mutation and an association with maternally inherited HCM combined with AVB. Our findings provide a new insight into the pathogenesis of HCM.

Splice, insertion-deletion and nonsense mutations that perturb the phenylalanine hydroxylase transcript cause phenylketonuria in India

Phenylketonuria (PKU) is an autosomal recessive metabolic disorder caused by mutational inactivation of the phenylalanine hydroxylase (PAH) gene. Missense mutations are the most common PAH mutation type detected in PKU patients worldwide. We performed PAH mutation analysis in 27 suspected Indian PKU families (including 7 from our previous study) followed by structure and function analysis of specific missense and splice/insertion-deletion/nonsense mutations, respectively. Of the 27 families, disease-causing mutations were detected in 25. A total of 20 different mutations were identified of which 7 "unique" mutations accounted for 13 of 25 mutation positive families. The unique mutations detected exclusively in Indian PKU patients included three recurrent mutations detected in three families each. The 20 mutations included only 5 missense mutations in addition to 5 splice, 4 each nonsense and insertion-deletion mutations, a silent variant in coding region and a 3'UTR mutation. One deletion and two nonsense mutations were characterized to confirm significant reduction in mutant transcript levels possibly through activation of nonsense mediated decay. All missense mutations affected conserved amino acid residues and sequence and structure analysis suggested significant perturbations in the enzyme activity of respective mutant proteins. This is probably the first report of identification of a significantly low proportion of missense PAH mutations from PKU families and together with the presence of a high proportion of splice, insertion-deletion, and nonsense mutations, points to a unique PAH mutation profile in Indian PKU patients.

Cardiac structural and sarcomere genes associated with cardiomyopathy exhibit marked intolerance of genetic variation

BACKGROUND

The clinical significance of variants in genes associated with inherited cardiomyopathies can be difficult to determine because of uncertainty regarding population genetic variation and a surprising amount of tolerance of the genome even to loss-of-function variants. We hypothesized that genes associated with cardiomyopathy might be particularly resistant to the accumulation of genetic variation.

METHODS AND RESULTS

We analyzed the rates of single nucleotide genetic variation in all known genes from the exomes of >5000 individuals from the National Heart, Lung, and Blood Institute's Exome Sequencing Project, as well as the rates of structural variation from the Database of Genomic Variants. Most variants were rare, with over half unique to 1 individual. Cardiomyopathy-associated genes exhibited a rate of nonsense variants, about 96.1% lower than other Mendelian disease genes. We tested the ability of in silico algorithms to distinguish between a set of variants in MYBPC3, MYH7, and TNNT2 with strong evidence for pathogenicity and variants from the Exome Sequencing Project data. Algorithms based on conservation at the nucleotide level (genomic evolutionary rate profiling, PhastCons) did not perform as well as amino acid-level prediction algorithms (Polyphen-2, SIFT). Variants with strong evidence for disease causality were found in the Exome Sequencing Project data at prevalence higher than expected.

CONCLUSIONS

Genes associated with cardiomyopathy carry very low rates of population variation. The existence in population data of variants with strong evidence for pathogenicity suggests that even for Mendelian disease genetics, a probabilistic weighting of multiple variants may be preferred over the single gene causality model.