Biology subjects

Barge-Schaapveld, D. Q. C. M.

Publications and source records attributed to Barge-Schaapveld, D. Q. C. M..

2 recordsLinked to original sources

bioRxiv2022

Reclassification of a likely pathogenic Dutch founder variant in KCNH2; implications of reduced penetrance

BackgroundVariants in KCNH2, encoding the hERG channel which is responsible for the rapid component of the cardiac delayed rectifier K+ current (IKr), are causal to Long QT Syndrome type 2 (LQTS2). We identified eight index patients with a new variant of unknown significance (VUS), KCNH2:c.2717C>T:p.(Ser906Leu). We aimed to elucidate the biophysiological effect of this variant, to enable reclassification and consequent clinical decision-making. MethodsA genotype-phenotype overview of the patients and relatives was created. The biophysiological effects were assessed by manual whole-cell patch-clamp using HEK293a cells expressing: (I) wild type (WT) KCNH2, (II) KCNH2-p.S906L alone (homozygous, Hm) or (III) KCNH2-p.S906L in combination with WT (1:1) (heterozygous, Hz). A calibrated automated patch-clamp assay using Flp-In HEK293 was used to follow up on the functional data. ResultsIncomplete penetrance of LQTS2 in KCNH2:p.(Ser906Leu) carriers was observed. In addition, some patients were heterozygous for other VUSs in CACNA1C, PKP2, RYR2, or AKAP9. The phenotype of carriers of KCNH2:p.(Ser906Leu) ranged from asymptomatic to life-threatening arrhythmic events. Manual patch-clamp showed a reduced current density by 69.8%, and 60.4% in KCNH2-p.S906L-Hm and KCNH2-p.S906L-Hz, respectively. The time constant of activation was significantly increased with 80.1% in KCNH2-p.S906L-Hm compared to KCNH2-WT. Assessment of KCNH2-p.S906L-Hz, by calibrated automatic patch-clamp showed a reduction in current density by 35.6%. ConclusionThe reduced current density in the KCNH2-p.S906L-Hz indicates a moderate loss of function. Combined with the reduced penetrance and variable phenotype, we conclude that KCNH2:p.(Ser906Leu) is a low penetrant likely pathogenic variant for LQTS2.

genetics↗

bioRxiv2021

Delineating the molecular and phenotypic spectrum of the SETD1B-related syndrome

Pathogenic variants in SETD1B have been associated with a syndromic neurodevelopmental disorder including intellectual disability, language delay and seizures. To date, clinical features have been described for eleven patients with (likely) pathogenic SETD1B sequence variants. We perform an in-depth clinical characterization of a cohort of 36 unpublished individuals with SETD1B sequence variants, describing their molecular and phenotypic spectrum. Selected variants were functionally tested using in vitro and genome-wide methylation assays. Our data present evidence for a loss-of-function mechanism of SETD1B variants, resulting in a core clinical phenotype of global developmental delay, language delay including regression, intellectual disability, autism and other behavioral issues, and variable epilepsy phenotypes. Developmental delay appeared to precede seizure onset, suggesting SETD1B dysfunction impacts physiological neurodevelopment even in the absence of epileptic activity. Interestingly, males are significantly overrepresented and more severely affected, and we speculate that sex-linked traits could affect susceptibility to penetrance and the clinical spectrum of SETD1B variants. Finally, despite the possibility of non-redundant contributions of SETD1B and its paralogue SETD1A to epigenetic control, the clinical phenotypes of the related disorders share many similarities, indicating that elucidating shared and divergent downstream targets of both genes will help to understand the mechanism leading to the neurobehavioral phenotypes. Insights from this extensive cohort will facilitate the counseling regarding the molecular and phenotypic landscape of newly diagnosed patients with the SETD1B-related syndrome.

genetics↗