Genome-wide analysis identifies MYH11 compound heterozygous variants leading to visceral myopathy corresponding to late-onset form of megacystis-microcolon-intestinal hypoperistalsis syndrome.

Megacystis-microcolon-hypoperistalsis-syndrome (MMIHS) is a rare and early-onset congenital disease characterized by massive abdominal distension due to a large non-obstructive bladder, a microcolon and decreased or absent intestinal peristalsis. While in most cases inheritance is autosomal dominant and associated with heterozygous variant in ACTG2 gene, an autosomal recessive transmission has also been described including pathogenic bialellic loss-of-function variants in MYH11. We report here a novel family with visceral myopathy related to MYH11 gene, confirmed by whole genome sequencing (WGS). WGS was performed in two siblings with unusual presentation of MMIHS and their two healthy parents. The 38 years-old brother had severe bladder dysfunction and intestinal obstruction, whereas the 30 years-old sister suffered from end-stage kidney disease with neurogenic bladder and recurrent sigmoid volvulus. WGS was completed by retrospective digestive pathological analyses. Compound heterozygous variants of MYH11 gene were identified, associating a deletion of 1.2 Mb encompassing MYH11 inherited from the father and an in-frame variant c.2578_2580del, p.Glu860del inherited from the mother. Pathology analyses of the colon and the rectum revealed structural changes which significance of which is discussed. Cardiac and vascular assessment of the mother was normal. This is the second report of a visceral myopathy corresponding to late-onset form of MMIHS related to compound heterozygosity in MYH11; with complete gene deletion and a hypomorphic allele in trans. The hypomorphic allele harbored by the mother raised the question of the risk of aortic disease in adults. This case shows the interest of WGS in deciphering complex phenotypes, allowing adapted diagnosis and genetic counselling.

Prevalence and phenotypes associated with ALPK3 null variants in a large French multicentric cohort: Confirming its involvement in hypertrophic cardiomyopathy.

Biallelic disease-causing variants in the ALPK3 gene were first identified in children presenting with a severe cardiomyopathy. More recently, it was shown that carriers of heterozygous ALPK3 null variants are at risk of developing hypertrophic cardiomyopathy (HCM) with an adult onset. Since the number of reported ALPK3 patients is small, the mutational spectrum and clinical data are not fully described. In this multi-centric study, we described the molecular and clinical spectrum of a large cohort of ALPK3 patients. Genetic testing using targeted next generation sequencing was performed in 16 183 cardiomyopathy index cases. Thirty-six patients carried at least one null ALPK3 variant. The five paediatric patients carried two ALPK3 variants, all presented an HCM phenotype with severe outcomes (one transplantation, one heart failure and one cardiac arrest). The 31 adult patients carried heterozygous variants and the main phenotype was HCM (n = 26/31); including 15% (n = 4) presented with an apical or a concentric form of hypertrophy. Reporting a large cohort of ALPK3 patients, this collaborative work confirmed a strong association with HCM and suggesting his screening in the context of idiopathic HCM.

Target population for a selective cardiac myosin inhibitor in hypertrophic obstructive cardiomyopathy: Real-life estimation from the French register of hypertrophic cardiomyopathy (REMY).

BACKGROUND: The efficacy of current pharmacological therapies in hypertrophic cardiomyopathy is limited. A cardiac myosin inhibitor, mavacamten, has recently been approved as a first-in-class treatment for symptomatic hypertrophic obstructive cardiomyopathy. AIMS: To assess the profile and burden of cardiac myosin inhibitor candidates in the hypertrophic cardiomyopathy prospective Register of hypertrophic cardiomyopathy (REMY) held by the French Society of Cardiology. METHODS: Data were collected at baseline and during follow-up from patients with hypertrophic cardiomyopathy enrolled in REMY by the three largest participating centres. RESULTS: Among 1059 adults with hypertrophic cardiomyopathy, 461 (43.5%) had obstruction; 325 (30.7%) of these were also symptomatic, forming the "cardiac myosin inhibitor candidates" group. Baseline features of this group were: age 58±15years; male sex (n=196; 60.3%); diagnosis-to-inclusion delay 5 (1-12)years; maximum wall thickness 20±6mm; left ventricular ejection fraction 69±6%; family history of hypertrophic cardiomyopathy or sudden cardiac death (n=133; 40.9%); presence of a pathogenic sarcomere gene mutation (n=101; 31.1%); beta-blocker or verapamil treatment (n=304; 93.8%), combined with disopyramide (n=28; 8.7%); and eligibility for septal reduction therapy (n=96; 29%). At the end of a median follow-up of 66 (34-106) months, 319 (98.2%) were treated for obstruction (n=43 [13.2%] received disopyramide), 46 (14.2%) underwent septal reduction therapy and the all-cause mortality rate was 1.9/100 person-years (95% confidence interval 1.4-2.6) (46 deaths). Moreover, 41 (8.9%) patients from the initial hypertrophic obstructive cardiomyopathy group became eligible for a cardiac myosin inhibitor. CONCLUSIONS: In this cohort of patients with hypertrophic cardiomyopathy selected from the REMY registry, one third were eligible for a cardiac myosin inhibitor.

Expanding the clinical spectrum of biglycan-related Meester-Loeys syndrome.

Pathogenic loss-of-function variants in BGN, an X-linked gene encoding biglycan, are associated with Meester-Loeys syndrome (MRLS), a thoracic aortic aneurysm/dissection syndrome. Since the initial publication of five probands in 2017, we have considerably expanded our MRLS cohort to a total of 18 probands (16 males and 2 females). Segregation analyses identified 36 additional BGN variant-harboring family members (9 males and 27 females). The identified BGN variants were shown to lead to loss-of-function by cDNA and Western Blot analyses of skin fibroblasts or were strongly predicted to lead to loss-of-function based on the nature of the variant. No (likely) pathogenic missense variants without additional (predicted) splice effects were identified. Interestingly, a male proband with a deletion spanning the coding sequence of BGN and the 5' untranslated region of the downstream gene (ATP2B3) presented with a more severe skeletal phenotype. This may possibly be explained by expressional activation of the downstream ATPase ATP2B3 (normally repressed in skin fibroblasts) driven by the remnant BGN promotor. This study highlights that aneurysms and dissections in MRLS extend beyond the thoracic aorta, affecting the entire arterial tree, and cardiovascular symptoms may coincide with non-specific connective tissue features. Furthermore, the clinical presentation is more severe and penetrant in males compared to females. Extensive analysis at RNA, cDNA, and/or protein level is recommended to prove a loss-of-function effect before determining the pathogenicity of identified BGN missense and non-canonical splice variants. In conclusion, distinct mechanisms may underlie the wide phenotypic spectrum of MRLS patients carrying loss-of-function variants in BGN.