Disease Penetrance Research Articles

Abstract 4115690: COL4A1-related Vascular Disease Displays Strikingly Different Penetrance, Onset, and Expressivity in Literature versus Biobank-Derived Cases

Monogenic cardiovascular diseases present throughout the human lifespan with varying symptoms. For most, our understanding of their penetrance, onset, and expressivity is derived from published case reports. The extent to which these literature-derived cases capture the full allelic and phenotypic spectrum is unknown, particularly since the literature is biased towards severe presentations. To illustrate, we investigated the penetrance (i.e. the presence of at least one symptom), onset, and phenotypic expressivity of a rare genetic disease linked to hemorrhagic stroke and other complications: COL4A1 -related vascular disease (COL4A1VD, or Gould Syndrome). We performed a systematic review of COL4A1VD cases reported in the biomedical literature ( N =459), normalizing their genetic variants and symptoms to controlled terminologies. We then investigated the phenotypic expression among COL4A1VD pathogenic variant carriers isolated from two population-scale biobanks (the UK Biobank and All of Us Research Program; combined N =714,246), identifying 178 subjects (prevalence: 0.025%) that should be at high risk for COL4A1VD-related symptoms. Based on the literature, the penetrance of COL4A1VD is approximately 92% (95% CI: 90%-95%), with each case expressing 4.3 symptoms on average. Neurologic complications were the most common finding, observed in 85% of symptomatic patients. Alternatively, the biobank-derived cohort displayed an overall enrichment for disease-related symptoms (COL4A1 pathogenic carriers are more likely to have increased symptom burden compared to non-carrier controls; P<0.005), but the penetrance of the variants was substantially reduced (34%; 95% CI: 26%-41%). In addition, this cohort expressed fewer symptoms on average (0.8 per carrier), with renal complications being far more common (78% of symptomatic biobank patients vs 22% of literature-derived cases; P < 0.001). Finally, the apparent age-of-onset was much later for the biobank-derived cohort (57-years vs 5-years for the literature cases). Most of these differences reflect the distinct ascertainment of these two COL4A1VD cohorts, but they also highlight our incomplete understanding of the true penetrance, expressivity, and onset for this rare disease. These results have important implications for COL4A1VD-related genetic counseling and surveillance, and they highlight a need for new methods that formally integrate the rare disease knowledge captured from these distinct data sources.

Abstract 4122035: The Distinct Natural History, Phenotype Spectrum, Familial Penetrance and Clinical Outcomes in Desmin ( DES )-Associated Cardiomyopathy

Background: Pathogenic/likely pathogenic variants (P/LP) in the desmin ( DES ) gene cause heterogeneous cardiomyopathy and skeletal myopathy phenotypes. Research Questions: Limited data suggest that patients with P/LP DES variants have a high incidence of major adverse cardiac events (MACEs), including cardiac conduction disease requiring pacemaker implantation (CCD-PM), sustained ventricular arrhythmias (VA), and heart failure (HF) events (HF hospitalization, heart transplant, HF-related death). However, small cohort sizes have limited full clinical characterization. Aims: We aimed to describe the natural history, phenotype spectrum, familial penetrance and MACE in patients with P/LP DES variants identified via clinical genetic testing. Methods: We conducted a systematic review and individual patient data meta-analysis of cardiac and skeletal myopathy phenotypes and MACE (CCD-PM, VA and HF events) in patients with P/LP DES variants by retrieving publications from Medline (PubMed) and Embase. Diagnosis of cardiomyopathy or MACE were both considered evidence of cardiac involvement. Results: Out of 4,212 screened records, 72 met inclusion criteria. In total, 230 patients were included (52.6% male, 52.2% probands, median age: 31 years at first evaluation [22.0; 42.8]). Eighty-five (37.0%) patients showed isolated cardiac involvement, 89 (38.7%) cardiac and skeletal muscle involvement, 39 (17.0%) only skeletal muscle involvement, and 17 (7.4%) had neither phenotype. Overall, 130 (56.5%) patients were diagnosed with a cardiomyopathy and 134 (57.4%) patients developed MACE (96 [41.7%] had CCD-PM, 36 [15.7%] sustained VA, and 43 [18.7%] HF events). Familial cardiac disease penetrance was 69.1% (76/110) in relatives with P/LP DES variants. Out of 40 patients who presented with isolated CCD-PM phenotype, 18 (45.0%) were diagnosed with a cardiomyopathy after 6 [2.0; 16.0] years of follow-up. In multivariable analysis, male sex and non-missense variants were associated with higher risk of sustained VA (HR 2.71, p=0.008, and HR 4.62, p<0.001, respectively) and HF events (HR 2.63, p=0.005, and HR 2.79, p=0.015). Conclusions: DES cardiomyopathy demonstrates a distinct natural history, characterized by high familial penetrance and a high MACE burden. Male patients and those carrying non-missense variants are at higher risk for sustained VA events and may benefit from primary preventive ICD implantation even in the absence of severe LV systolic dysfunction.

Abstract 4120763: Predicting Disease Risk Among Variants in Cardiomyopathy-Associated Genes Across Diverse Genetic Ancestries

Background: Many cases of cardiomyopathy (CM) are genetically inherited, and the expansion of broad genomic sequencing has opened the door for predicting those at risk for developing disease. However, genetic tools that help determine variant pathogenicity employ genetic data from predominantly European genetic ancestries. Understanding the full diversity of genetic variants in cardiomyopathy genes is central to identifying which variants will cause disease. Hypothesis: Participants of non-European genetic ancestry will have a higher burden of cardiomyopathy gene variants with "VUS" designation in ClinVar but will have equivalent/less penetrance of clinical cardiomyopathy compared to a European ancestry group. Methods: Participants in the AllofUs database with exome sequencing (ES) were queried and a cohort of 230,013 participants were retained after sample quality control filters. Participant genetic ancestry was based on the designated ancestry group determined via AllofUs as previously described (1). Participants were queried for variants in genes with definitive or moderate evidence of hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), and arrhythmogenic cardiomyopathy (ACM) in ClinGen. Variants were filtered by ClinVar status (1* and above P/LP, 1* and above B/LB, and VUS). Participant CM disease status was determined via ICD-9/10 code. Results: For each ancestry group, prevalence of cardiomyopathy ranged from 0.34% in the Latino/admixed American ancestry group to 1.09% in the African group, with an average prevalence of 0.91% across all groups. The European group had a statistically significant lower percentage of ClinVar VUS variants at 26%, while all other non-European ancestry groups had a combined VUS prevalence rate of 35% (****p<0.0001). The penetrance of CM in participants with CM VUS variants was lower in combined non-European ancestry groups (0.84%) than European ancestry (1.02%) (*p=0.0156). Conclusion: Prevalence of ClinVar VUS variants varies across different genetic ancestry groups, with European ancestry having a lower burden of VUS variants compared to non-European groups. However, non-European ancestry groups with increased burden of VUS variants have lower disease penetrance. Citations: (1) The All of Us Research Program Genomics Investigators. Genomic data in the All of Us Research Program. Nature 627 , 340–346 (2024). https://doi.org/10.1038/s41586-023-06957-x

Can variants of genes associated with familial heart block predict conduction disease in the general population? A UK Biobank study.

Abstract Background Progressive familial heart block is a genetic disease that can present with worsening cardiac conduction disease (CCD) and risk of life-threatening bradycardia. The prevalence, penetrance, and expressivity of known rare pathogenic/likely pathogenic variants (P/LP) in the general population is unclear. In addition, the role of common genetic variation in this phenotypic expression is unknown. Understanding this is essential for patient management in clinic. Purpose 1). To investigate the prevalence of variants linked with early-onset CCD and phenotypic expression in a large biobank. 2). To investigate whether a PR interval polygenic risk score (PRS) improves risk prediction. Methods Early-onset conduction disease P/LP or variants of uncertain significance (VUS) were identified from ClinVar, genetic testing reports at a teaching hospital (6 variants), and the literature, mapping to 22 genes. From the full UK Biobank prospective cohort, 469,511 participants passed genetic quality control and were assigned to P/LP, VUS, or genotype negative (G-) groups, using whole exome sequencing analysed with bcftools. A PR-PRS was constructed using weights from a published meta-analysis excluding UKB data. The primary outcome was CCD (atrioventricular (AV) block, bundle branch block, pacemaker or ICD implantation) and secondary outcomes were high-grade AV block or pacemaker insertion, compared with lifetime risk Cox proportional hazards controlled for sex and age as a timescale. Results 55% of participants were female, 95% had European ancestry, and average age at censor was 71 years. There were 25 P/LP carriers, and 8,862 with a VUS, in 6 genes (MYH7, SCN5A, TNNI3K, TRPM4, TTN, and LMNA). Major demographic factors were the same between groups. CCD was significantly more prevalent in P/LP individuals (28% vs 5.8% in VUS vs 5.5% in G-; p<0.001) with a hazard ratio of HR 6.47 [95% CI=3.09-13.6] vs G-. This was driven by AV block and pacemaker implantation (HR 23.2 [95% CI=8.69-61.8] and 13.4 [95% CI=6.01-29.8], respectively). Results were similar in an unrelated subset and controlling for ischaemic heart disease and heart failure. The 7 P/LP individuals with conduction disease were mostly linked to a single LMNA variant (4 out of 6 carriers with penetrant disease). In the full cohort, the PR-PRS was predictive of CCD (HR=1.07 [95% CI=1.06-1.08]), AV block (HR=1.09 [95% CI=1.06-1.13]), and pacemaker implantation (HR=1.04 [95% CI=1.02-1.06]). When combined with P/LP status, both PR-PRS (HR=1.07 [95% CI=1.06-1.08]) and P/LP (HR=6.42 [95% CI=3.06-13.5]) were independent predictors of CCD. Conclusion(s) Rare variant carrier status predicts a 6.5-fold increased lifetime risk of CCD, a 23-fold increased risk of AV block and 13-fold risk for pacemaker requirement. However, phenotypic expression for some variants is highly variable. A PR-PRS captures risk independent of P/LP variants and warrants further investigation with updated PRS construction methods.

Exploring the diagnostic yield of family screening and genetic testing in adolescent individuals with pre-clinical phenotypes

Abstract Introduction Family screening and genetic testing are key components in the management strategy of individuals diagnosed with an inherited cardiac condition (ICC). Disease penetrance for most ICCs, notably cardiomyopathies is age dependent, which is why a more permissive approach towards family screening is adopted in young individuals with a pre-clinical phenotype. Study Objectives The main objective of this study was to explore the role of family screening and genetic testing in adolescent subjects with a pre-clinical phenotype has not been formally explored. Methodology Adolescent probands with a pre-clinical phenotype following a national cardiac screening program (BEAT-IT) were offered genetic testing and family screening. Probands with anterior TWI were rescreened at 16 years. Only those with persistent changes were enrolled in the study. Genetic counselling was also offered to probands and relatives. Testing was initially offered to first degree relatives. Cascade testing (clinical and genetic) was also offered to other generations if a screened relative satisfied one or more of these conditions i) phenotype positive, ii) pre-clinical phenotype, iii) clinically relevant genotype. Results 16 probands (mean age 15 years) were identified with a pre-clinical phenotype. All had an abnormal ECG (9=inferior/lateral TWI, 6=anterior TWI, 1=ST depression). A comprehensive evaluation was otherwise normal. Half were gene positive (G+), 4 had clinically relevant genotypes (n=4 inferior/lateral TWI). These were classified as likely pathogenic according to ACMG criteria (n=2 MYH7, n=1 ACTC1, n=1 MYBPC3). 71 family members were subsequently screened (59.2% female, median 43Y [IQR 27] at evaluation, 11.3% <18Y at evaluation, 67.6% first degree relatives). A substantial proportion (n=13, 18.3%) were referred for further evaluation. Two (2/8, 25.0%) were <18Y. An abnormal ECG was the commonest reason for referral (n=9, 12.7%). Three (4.2%) were given a diagnosis (n=2 HCM [both MYH7}, n=1 DCM [ACTC1]). Seven (9.9%) were referred because of an abnormal ECG (n=3 inferolateral TWI, n=2 ventricular ectopics, n=1 anterolateral TWI, n=1 ST depression). Four were G+ and were offered surveillance. Fourteen (19.7%) were offered family screening because of incorporating genetic testing into the study protocol. Genetics altered the evaluation strategy in 16.9% of screened relatives. More in-depth cascade testing identified 6 (8.5%) individuals who needed follow-up (n=1 diagnosis [DCM], n=1 abnormal ECG, n=4 G+). Gene negative individuals (6, 8.5%) were safely reassured and discharged. Conclusion Family screening in adolescent probands with pre-clinical phenotypes offers a reasonable diagnostic yield (4.2% diagnosis, 14.1% surveillance). Incorporating genetic testing into the evaluation protocol offers a more personalized strategy, altering management in a significant proportion of screened relatives (16.9%).

Promise and Peril of a Genotype-First Approach to Mendelian Cardiovascular Disease.

Precision medicine, which among other aspects includes an individual's genomic data in diagnosis and management, has become the standard-of-care for Mendelian cardiovascular disease (CVD). However, early identification and management of asymptomatic patients with potentially lethal and manageable Mendelian CVD through screening, which is the promise of precision health, remains an unsolved challenge. The reduced costs of genomic sequencing have enabled the creation of biobanks containing in-depth genetic and health information, which have facilitated the understanding of genetic variation, penetrance, and expressivity, moving us closer to the genotype-first screening of asymptomatic individuals for Mendelian CVD. This approach could transform health care by diagnostic refinement and facilitating prevention or therapeutic interventions. Yet, potential benefits must be weighed against the potential risks, which include evolving variant pathogenicity assertion or identification of variants with low disease penetrance; costly, stressful, and inappropriate diagnostic evaluations; negative psychological impact; disqualification for employment or of competitive sports; and denial of insurance. Furthermore, the natural history of Mendelian CVD is often unpredictable, making identification of those who will benefit from preventive measures a priority. Currently, there is insufficient evidence that population-based genetic screening for Mendelian CVD can reduce adverse outcomes at a reasonable cost to an extent that outweighs the harms of true-positive and false-positive results. Besides technical, clinical, and financial burdens, ethical and legal aspects pose unprecedented challenges. This review highlights key developments in the field of genotype-first approaches to Mendelian CVD and summarizes challenges with potential solutions that can pave the way for implementing this approach for clinical care.

HAPLN3 p.T34A contributes to incomplete penetrance of moyamoya disease in Chinese carrying RNF213 p.R4810K.

The penetrance of the RNF213 p.R4810K, a founder mutation of moyamoya disease (MMD), is estimated to be only 1/150-1/300. However, the factors affecting its penetrance remain unclear. Therefore, our study aims to identify modifier genes associated with the incomplete penetrance of this founder mutation. Whole-exome sequencing (WES) was performed on 36 participants, including 22 MMD patients and 14 non-MMD controls with RNF213 p.R4810K mutation. Fisher's exact test was used to assess the presence of genetic variants that differed significantly between MMD patients and non-MMD controls. In order to exclude false-positive results, another 55 carriers were included to perform Fisher's exact test for the selected sites in the WES discovery stage. Subsequently, human brain microvascular endothelial cells were transfected with wild-type and mutant HAPLN3 for tube formation assays and western blotting to explore the impact of candidate genes on angiogenesis. Analysis of variants from WES data revealed a total of 12 non-synonymous variants. Through bioinformatics analysis, the focus was on the HAPLN3 p.T34A variant with a significant p value of 0.00731 in Fisher's exact test. Validation through Sanger sequencing confirmed the presence of this variant in the WES data. Invitro experiments revealed that silencing HAPLN3 and transfecting HAPLN3 p.T34A significantly enhanced tube formation and increased the relative protein expression of vascular endothelial growth factor in endothelial cells. These results suggest that HAPLN3 may function as a modifier gene of RNF213 p.R4810K, promoting the development of MMD and contributing to the incomplete penetrance of MMD founder mutations.

Reproductive options and genetic testing for patients with an inherited cardiac disease.

In the past decade, genetic testing for cardiac disease has become part of routine clinical care. A genetic diagnosis provides the possibility to clarify risk for relatives. For family planning, a genetic diagnosis provides reproductive options, including prenatal diagnosis and preimplantation genetic testing, that can prevent an affected parent from having a child with the genetic predisposition. Owing to the complex genetic architecture of cardiac diseases, characterized by incomplete disease penetrance and the interplay between monogenic and polygenic variants, the risk reduction that can be achieved using reproductive genetic testing varies among individuals. Globally, disparities, including regulatory and financial barriers, in access to reproductive genetic tests exist. Although reproductive options are gaining a prominent position in the management of patients with inherited cardiac diseases, specific policies and guidance are lacking. Guidelines recommend that prenatal diagnosis and preimplantation genetic testing are options that should be discussed with families. Health-care professionals should, therefore, be aware of the possibilities and feel confident to discuss the benefits and challenges. In this Review, we provide an overview of the reproductive options in the context of inherited cardiac diseases, covering the genetic, technical, psychosocial and equity considerations, to prepare health-care professionals for discussions with their patients.

Examining the clinical and genetic spectrum of maturity-onset diabetes of the young (MODY) in Iran

Maturity-onset diabetes of the young (MODY) is an uncommon monogenic type of diabetes mellitus. Detecting genetic variants for MODY is a necessity for precise diagnosis and treatment. The majority of MODY genetic predisposition has been documented in European populations and a lack of information is present in Iranians which leads to misdiagnosis as a consequence of defects in unknown variants. In this study, using genetic variant information of 20,002 participants from the family-based TCGS (Tehran Cardiometabolic Genetic Study) cohort, we evaluated the genetic spectrum of MODY in Iran. We concentrated on previously discovered MODY-causing genes. Genetic variants were evaluated for their pathogenicity. We discovered 6 variants that were previously reported in the ClinVar as pathogenic/likely pathogenic (P/LP) for MODY in 45 participants from 24 families (INS in 21 cases, GCK in 13, HNF1B in 8, HNF4A, HNF1A, and CEL in 1 case). One potential MODY variant with Uncertain Risk Allele in ClinVar classification was also identified, which showed complete disease penetrance (100%) in four subjects from one family. This is the first family-based study to define the genetic spectrum and estimate the prevalence of MODY in Iran. The discovered variants need to be investigated by additional studies.

Natural History, Phenotype Spectrum and Clinical Outcomes of Desmin (DES)-Associated Cardiomyopathy.

Pathogenic/likely pathogenic (P/LP) desmin (DES) variants cause heterogeneous cardiomyopathy and/or skeletal myopathy phenotypes. Limited data suggest a high incidence of major adverse cardiac events (MACE), including cardiac conduction disease (CCD), sustained ventricular arrhythmias (VA), and heart failure (HF) events (HF hospitalization, LVAD/cardiac transplant, HF-related death), in patients with P/LP DES variants. However, pleiotropic presentation and small cohort sizes have limited clinical phenotype and outcome characterization. We aimed to describe the natural history, phenotype spectrum, familial penetrance and outcomes in patients with P/LP DES variants through a systematic review and individual patient data meta-analysis using published reports. We searched Medline (PubMed) and Embase for studies that evaluated cardiac phenotypes in patients with P/LP DES variants. Cardiomyopathy diagnosis or occurrence of MACE were considered evidence of cardiac involvement/penetrance. Lifetime event-free survival from CCD, sustained VA, HF events, and composite MACE was assessed. Out of 4,212 screened publications, 71 met the inclusion criteria. A total of 230 patients were included (52.6% male, 52.2% probands, median age: 31 years [22.0; 42.8] at first evaluation, median follow-up: 3 years [0; 11.0]). Overall, 124 (53.9%) patients were diagnosed with cardiomyopathy, predominantly dilated cardiomyopathy (14.8%), followed by restrictive cardiomyopathy (13.5%), whereas other forms were less common: arrhythmogenic cardiomyopathy (7.0%), hypertrophic cardiomyopathy (6.1%), arrhythmogenic right ventricular cardiomyopathy (5.2%), and other forms (7.4%). Overall, 132 (57.4%) patients developed MACE, with 96 [41.7%] having CCD, 36 [15.7%] sustained VA, and 43 [18.7%] HF events. Familial penetrance of cardiac disease was 63.6% among relatives with P/LP DES variants. Male sex was associated with increased risk of sustained VA (HR 2.28, p=0.02) and HF events (HR 2.45, p=0.008). DES cardiomyopathy exhibits heterogeneous phenotypes and distinct natural history, characterized by high familial penetrance and substantial MACE burden. Male patients face higher risk of sustained VA events.

Clinical Outcome of Hypertrophic Cardiomyopathy in Probands with the Founder Variant c.913_914del in MYBPC3: A Slovenian Cohort Study.

Hypertrophic cardiomyopathy is often caused by pathogenic MYBPC3 variants. The study of Italian patients with HCM and MYBPC3(NM_000256.3):c.913_914del showed a higher disease penetrance in males and a higher frequency of arrhythmias compared to patients with other likely pathogenic and pathogenic (LP/P) MYBPC3 variants. We investigated the clinical outcomes of Slovenian probands with MYBPC3 LP/P variants, estimated the variant penetrance and compared the results with an Italian study. We identified 31 haplotype-matched individuals with MYBPC3:c.913_914del and 34 individuals with other LP/P MYBPC3 variants. We observed some significant differences in clinical and echocardiographic characteristics and frequency of adverse cardiac events between Slovenian and Italian probands with MYBPC3:c913_914del. We were unable to replicate previous findings for MYBPC3:c.913_914del, highlighting the complexity of genotype-phenotype associations.

Acute intermittent porphyria: a disease with low penetrance and high heterogeneity.

Acute intermittent porphyria (AIP) is caused by mutations in the gene encoding hydroxymethylbilane synthase (HMBS), a key enzyme in the heme biosynthesis pathway. AIP is an autosomal dominant disorder characterized by low penetrance and a highly heterogenous clinical presentation. The estimated prevalence of AIP is 5-10 cases per 100,000 persons, with acute attacks manifesting in less than 1% of the at-risk population. This low frequency of attacks suggests significant roles for oligogenic inheritance and environmental factors in the pathogenesis of the disease. In recent years, identification of several modifier genes has advanced our understanding of the factors influencing AIP penetrance and disease severity. This review summarizes these factors including the impact of specific HMBS mutations, oligogenic inheritance, mitochondrial DNA copy number, age, sex, the influence of sex hormones, and the role of environmental factors. Further studies into the etiology of AIP disease penetrance should inform pathogenesis, potentially allowing for the development of more precise diagnostic and therapeutic approaches.

Abstract Mo080: Clinically Variable Penetrant MYH7 G256E Mutation Shows Gene-Dose-Dependent HCM Disease Phenotype on a Transcriptomic, Proteomic, and Functional Level

Introduction: Hypertrophic cardiomyopathy (HCM) is a monogenic disorder caused by heterozygous (HET) mutations in sarcomere genes such as MYH7 . Recently, human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying HET HCM mutations have shed new insights into the molecular mechanisms of HCM. However, the cause of phenotype variability and the role of allelic imbalance in phenotype penetrance of HET missense mutations such as MYH7 G256E remain unclear. Hypothesis: We hypothesize that hiPSC CMs carrying clinically variable penetrant HCM missense mutations such as MYH7 G256E show a gene dose-dependent disease phenotype indicating their susceptibility for allelic imbalance as a cause for variable disease phenotype penetrance. Methods: We generated HET and homozygous (HOM) hiPSC-lines for variable penetrant HCM mutation MYH7 G256E. We performed multiplexed single-cell RNA sequencing and quantitative proteomics analyses on wildtype (WT), HET, and HOM iPSC-CMs at day 30 of cardiac differentiation. Additional Digital Droplet PCR studies were performed to investigate the MYH7 mutant allele expression. The functional contractile phenotype was assessed with Sony SI8000 Cell motion imaging system. Results: We detected a large clone-to-clone and batch-to-batch variability in HET iPSC-CMs on a transcriptomic and proteomic level that obscured the identification of a consistent mutant phenotype in HET MYH7 G256E vs WT CMs. These phenotypes correlated with a 1:1 bulk ratio of mutant vs WT mRNA and protein expression, while overall MYH7 gene and protein expression remained comparable. Transcriptomic and proteomic analyses of WT, HET, and HOM CMs show a gene dose-dependent regulation of known hypertrophy response markers such as NPPB (mRNA: HET vs WT: +1.76x p .adj=7.0*10 -7 , HOM vs WT: +5.42x p.adj=1.5*10 -48 ; protein: HET vs WT: +1.15x, 95% CI [0.86, 1.58]; HOM vs WT: +1.51x, 95% CI [1.12, 2.01]) which functionally correlated with enhanced contractility (contraction velocity in μm/s: WT: 5.84 +/-2.24, HET: 6.04 +/-2.89, HOM: 7.77 +/-3.352, p=0.3*10 -2 ANOVA) and the more frequent occurrence of arrhythmias (WT: 1/46, HET: 0/55, HOM: 5/41). Conclusions: Hypertrophic disease phenotype in MYH7 G256E mutation iPSC-CMs shows a gene dose-dependent penetrance on a transcriptomic, proteomic, and functional level. This indicates susceptibility to allelic imbalance as a potential cause for variable disease penetrance.

Comprehensive Analysis of a Japanese Pedigree with Biallelic ACAGG Expansions in RFC1 Manifesting Motor Neuronopathy with Painful Muscle Cramps.

Cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS) is an autosomal recessive multisystem neurologic disorder caused by biallelic intronic repeats in RFC1. Although the phenotype of CANVAS has been expanding via diagnostic case accumulation, there are scant pedigree analyses to reveal disease penetrance, intergenerational fluctuations in repeat length, or clinical phenomena (including heterozygous carriers). We identified biallelic RFC1 ACAGG expansions of 1000 ~ repeats in three affected siblings having sensorimotor neuronopathy with spinocerebellar atrophy initially presenting with painful muscle cramps and paroxysmal dry cough. They exhibit almost homogeneous clinical and histopathological features, indicating motor neuronopathy. Over 10years of follow-up, painful intractable muscle cramps ascended from legs to trunks and hands, followed by amyotrophy and subsequent leg pyramidal signs. The disease course combined with the electrophysical and imagery data suggest initial and prolonged hyperexcitability and the ensuing spinal motor neuron loss, which may progress from the lumbar to the rostral anterior horns and later expand to the corticospinal tract. Genetically, heterozygous ACAGG expansions of similar length were transmitted in unaffected family members of three successive generations, and some of them experienced muscle cramps. Leukocyte telomere length assays revealed comparatively shorter telomeres in affected individuals. This comprehensive pedigree analysis demonstrated a non-anticipating ACAGG transmission and high penetrance of manifestations with a biallelic state, especially motor neuronopathy in which muscle cramps serve as a prodromal and disease progress marker. CANVAS and RFC1 spectrum disorder should be considered when diagnosing lower dominant motor neuron disease, idiopathic muscle cramps, or neuromuscular hyperexcitability syndromes.

Pathophysiology of hypereosinophilia-associated heart disease.

Cardiac complications in patients with hypereosinophilia cause significant morbidity and mortality. However, mechanisms of how eosinophilic inflammation causes heart damage are poorly understood. We developed a model of hypereosinophilia-associated heart disease by challenging hypereosinophilic mice with peptide from the cardiac myosin heavy chain. Disease outcomes were measured by histology, immunohistochemistry, flow cytometry, and measurement of cells and biomarkers in peripheral blood. Eosinophil dependence was determined by using eosinophil-deficient mice (ΔdblGATA). Single cells from heart were subjected to single cell RNA sequencing to assess cell composition, subtypes and expression profiles. Mice challenged with myocarditic and control peptide had peripheral blood leukocytosis, but only those challenged with myocarditic peptide had heart inflammation. Heart tissue was infiltrated by eosinophil-rich inflammatory infiltrates associated with cardiomyocyte damage. Disease penetrance and severity were dependent on the presence of eosinophils. Single cell RNA sequencing showed enrichment of myeloid cells, T-cells and granulocytes (neutrophils and eosinophils) in the myocarditic mice. Macrophages were M2 skewed, and eosinophils had an activated phenotype. Gene enrichment analysis identified several pathways potentially involved in pathophysiology of disease. Eosinophils are required for heart damage in hypereosinophilia-associated heart disease. Additionally, myeloid cells, granulocytes and T-cell cooperatively or independently participate in the pathogenesis of hypereosinophilia-associated heart disease.

Exploring penetrance of clinically relevant variants in over 800,000 humans from the Genome Aggregation Database.

Incomplete penetrance, or absence of disease phenotype in an individual with a disease-associated variant, is a major challenge in variant interpretation. Studying individuals with apparent incomplete penetrance can shed light on underlying drivers of altered phenotype penetrance. Here, we investigate clinically relevant variants from ClinVar in 807,162 individuals from the Genome Aggregation Database (gnomAD), demonstrating improved representation in gnomAD version 4. We then conduct a comprehensive case-by-case assessment of 734 predicted loss of function variants (pLoF) in 77 genes associated with severe, early-onset, highly penetrant haploinsufficient disease. We identified explanations for the presumed lack of disease manifestation in 701 of the variants (95%). Individuals with unexplained lack of disease manifestation in this set of disorders rarely occur, underscoring the need and power of deep case-by-case assessment presented here to minimize false assignments of disease risk, particularly in unaffected individuals with higher rates of secondary properties that result in rescue.

Postoperative Crohn's Disease Recurrence Risk and Optimal Biologic Timing After Temporary Diversion Following Ileocolic Resection.

Postoperative recurrence of Crohn's disease (CD) is common. While most patients undergo resection with undiverted anastomosis (UA), some individuals also have creation of an intended temporary diversion (ITD) with an ileostomy followed by ostomy takedown (OT) due to increased risk of anastomotic complications. We assessed the association of diversion with subsequent CD recurrence risk and the influence of biologic prophylaxis timing to prevent recurrence in this population. This was a retrospective cohort study of CD patients who underwent ileocolic resection between 2009 and 2020 at a large quaternary health system. Patients were grouped by continuity status after index resection (primary anastomosis or ITD). The outcomes of the study were radiographic, endoscopic, and surgical recurrence as well as composite recurrence postoperatively (after OT in the ITD group). Propensity score-weighted matching was performed based on risk factors for diversion and recurrence. Multivariable regression and a Cox proportional hazards model adjusting for recurrence risk factors were used to assess association with outcomes. Subgroup analysis in the ITD group was performed to assess the impact of biologic timing relative to OT (no biologic, biologic before OT, after OT) on composite recurrence. A total of 793 CD patients were included (mean age 38 years, body mass index 23.7kg/m2, 52% female, 23% active smoker, 50% penetrating disease). Primary anastomosiswas performed in 67.5% (n = 535) and ITD in 32.5% (n = 258; 79% loop, 21% end) of patients. Diverted patients were more likely to have been males and to have had penetrating and perianal disease, prior biologic use, lower body mass index, and lower preoperative hemoglobin and albumin (all P < .01). After a median follow-up of 44 months, postoperative recurrence was identified in 83.3% patients (radiographic 40.4%, endoscopic 39.5%, surgical 13.3%). After propensity score matching and adjusting for recurrence risk factors, no significant differences were seen between continuity groups in radiographic (adjusted hazard ratio [aHR], 1.32; 95% confidence interval [CI], 0.91-1.91) or endoscopic recurrence (aHR, 1.196; 95% CI, 0.84-1.73), but an increased risk of surgical recurrence was noted in the ITD group (aHR, 1.61; 95% CI, 1.02-2.54). Most (56.1%) ITD patients started biologic prophylaxis after OT, 11.4% before OT, and 32.4% had no postoperative biologic prophylaxis. Biologic prophylaxis in ITD was associated with younger age (P < .001), perianal disease (P = .04), and prior biologic use (P < .001) but not in recurrence (P = .12). Despite higher rates of objective disease activity identified before OT, biologic exposure before OT was not associated with a significant reduction in composite post-OT recurrence compared with starting a biologic after OT (52% vs 70.7%; P = 0.09). Diversion of an ileocolic resection is not consistently associated with a risk of postoperative recurrence and should be performed when clinically appropriate. Patients requiring diversion at time of ileocolic resection are at high risk for recurrence, and biologic initiation prior to stoma reversal may be considered.

#2613 Clinical spectrum and prognosis of the atypical polycystic kidney disease caused by monoallelic loss-of-function IFT140 variants

Abstract Background and Aims Monoallelic loss-of-function (LoF) variants in IFT140, which protein product is involved in retrograde ciliary trafficking and ciliary entry of membrane protein, have been recently linked to ADPKD spectrum, with 44 pedigrees reported so far [1]. The aim of this study was to characterize the disease presentation and renal outcome of individuals with monoallelic LoF variants of IFT140. Method Clinical information, family history and imaging data were collected for individuals with LoF IFT140-variants identified amongst 2800 individuals recruited in the Genkyst and Cystic ADPKD patients cohorts, and in different French, Spanish, and German centers. Targeted massive parallel sequencing of cystic genes or whole exome sequencing was performed. Newly identified and recently reported cases were combined to evaluate the influence of sex on eGFR using linear regression taking age into account. In addition, data of the Genome Aggregation (GnomAD) v4.0 and of the 100k Genomes project were respectively used to explore genetic prevalence and disease penetrance and expressivity. Results A total of 75 individuals from 61 pedigrees were identified (median age at last follow-up 56 years, 52% females). Forty-one different LoF IFT140-variants were identified: 14 nonsense, 7 splice-site, 14 frameshifting deletions or insertions and 6 large deletions, and no additional pathogenic variant was identified in any other gene. A majority of the individuals presented with large, exophytic cysts, median total kidney volume 688 (n = 35, range 201-4139) ml, and 90.9% were classified in Mayo Class 2A. Although 70.4% of the individuals had stage 1 or 2 chronic kidney disease (CKD) at the last follow up, proportion of CKD stage 3-5 was significantly higher (56.3% vs 7.7%, p &amp;lt; 0.00001) after 60 years of age. Adjusted for age, males exhibited lower eGFR (linear regression, p = 0.038, Fig. 1). Median age at diagnosis of hypertension was 63 years. Liver cysts were present in 12% of affected individuals with no case of symptomatic polycystic liver disease, and intracranial aneurysms in three of 10 screened patients. The genetic prevalence of monoallelic LoF IFT140 variants was estimated to be 19.56 (0.95 CI 18.60-20.53) per 10,000 in the entire GnomAD population (n = 280 in 807,162) and 29.4 (0.95 CI 25.4-33.8) per 10,000 in the 100kG (n = 190 in 64,185). Amongst the latter, kidney cysts were reported in 26.8% and diagnosis cystic kidney disease (Q61) was established in 18.4%. No obvious extra renal manifestations were identified, and out of total of 730 phenotype association tests conducted, only Q61 was associated with pLOF IFT140 variants (p = 2.9 × 10−9, OR = 5.6 (3.3-9.2)). Conclusion Individuals with monoallelic LoF variants of IFT140 are likely to develop kidney cysts and/or atypical forms of ADPKD. However, a large proportion may remain asymptomatic or undiagnosed. There is no evidence to recommend cascade screening using genetic testing in young at risk relatives. Follow-up of blood pressure and eGFR after 50 years of age should be advised.

Striatal cholinergic interneuron development in models of DYT1 dystonia

Dystonia is a neurodevelopmental disorder characterized by severe involuntary twisting movements, hypothesized to arise from a dysfunctional motor network involving the cortex, basal ganglia, and cerebellum. Within this network, striatal cholinergic interneurons have been identified as possible contributors to dystonia pathophysiology. However, little is known about striatal cholinergic interneuron development in the mammalian brain, limiting our understanding of its role in dystonia and therapeutic potential. Here, I review striatal cholinergic interneuron development in the context of early-onset DYT1 (or “DYT-TOR1A”) dystonia. I discuss clinical and laboratory research findings that support cholinergic dysfunction in DYT1 dystonia and the implications of abnormal cholinergic cell development on disease penetrance and striatal connectivity.

PURA syndrome-causing mutations impair PUR-domain integrity and affect P-body association.

Mutations in the human PURA gene cause the neurodevelopmental PURA syndrome. In contrast to several other monogenetic disorders, almost all reported mutations in this nucleic acid-binding protein result in the full disease penetrance. In this study, we observed that patient mutations across PURA impair its previously reported co-localization with processing bodies. These mutations either destroyed the folding integrity, RNA binding, or dimerization of PURA. We also solved the crystal structures of the N- and C-terminal PUR domains of human PURA and combined them with molecular dynamics simulations and nuclear magnetic resonance measurements. The observed unusually high dynamics and structural promiscuity of PURA indicated that this protein is particularly susceptible to mutations impairing its structural integrity. It offers an explanation why even conservative mutations across PURA result in the full penetrance of symptoms in patients with PURA syndrome.