Syndactyly

Timothy syndrome (TS) is a severe, multisystem disorder characterized by autism, epilepsy, long-QT syndrome and other neuropsychiatric conditions1. TS type 1 (TS1) is caused by a gain-of-function variant in the alternatively spliced and developmentally enriched CACNA1C exon 8A, as opposed to its counterpart exon 8. We previously uncovered several phenotypes in neurons derived from patients with TS1, including delayed channel inactivation, prolonged depolarization-induced calcium rise, impaired interneuron migration, activity-dependent dendrite retraction and an unanticipated persistent expression of exon 8A2-6. We reasoned that switching CACNA1C exon utilization from 8A to 8 would represent a potential therapeutic strategy. Here we developed antisense oligonucleotides (ASOs) to effectively decrease the inclusion of exon 8A in human cells both in vitro and, following transplantation, in vivo. We discovered that the ASO-mediated switch from exon 8A to 8 robustly rescued defects in patient-derived cortical organoids and migration in forebrain assembloids. Leveraging a transplantation platform previously developed7, we found that a single intrathecal ASO administration rescued calcium changes and in vivo dendrite retraction of patient neurons, suggesting that suppression of CACNA1C exon 8A expression is a potential treatment for TS1. Broadly, these experiments illustrate how a multilevel, in vivo and in vitro stem cell model-based approach can identify strategies to reverse disease-relevant neural pathophysiology.

Timothy Syndrome (TS) is a multisystem disorder, prominently featuring cardiac action potential prolongation with paroxysms of life-threatening arrhythmias. The underlying defect is a single de novo missense mutation in CaV1.2 channels, either G406R or G402S. Notably, these mutations are often viewed as equivalent, as they produce comparable defects in voltage-dependent inactivation and cause similar manifestations in patients. Yet, their effects on calcium-dependent inactivation (CDI) have remained uncertain. Here, we find a significant defect in CDI in TS channels, and uncover a remarkable divergence in the underlying mechanism for G406R versus G402S variants. Moreover, expression of these TS channels in cultured adult guinea pig myocytes, combined with a quantitative ventricular myocyte model, reveals a threshold behaviour in the induction of arrhythmias due to TS channel expression, suggesting an important therapeutic principle: a small shift in the complement of mutant versus wild-type channels may confer significant clinical improvement.

BackgroundApert syndrome is characterized by craniosynostosis and limb abnormalities and is primarily caused by FGFR2 +/P253R and +/S252W mutations. The former mutation is present in approximately one third whereas the latter mutation is present in two-thirds of the patients with this condition. We previously reported an inbred transgenic mouse model with the Fgfr2 +/S252W mutation on the C57BL/6J background for Apert syndrome. Here we present a mouse model for the Fgfr2+/P253R mutation.ResultsWe generated inbred Fgfr2(+/P253R) mice on the same C56BL/6J genetic background and analyzed their skeletal abnormalities. 3D micro-CT scans of the skulls of the Fgfr2(+/P253R) mice revealed that the skull length was shortened with the length of the anterior cranial base significantly shorter than that of the Fgfr2(+/S252W) mice at P0. The Fgfr2(+/P253R) mice presented with synostosis of the coronal suture and proximate fronts with disorganized cellularity in sagittal and lambdoid sutures. Abnormal osteogenesis and proliferation were observed at the developing coronal suture and long bones of the Fgfr2(+/P253R) mice as in the Fgfr2(+/S252W) mice. Activation of mitogen-activated protein kinases (MAPK) was observed in the Fgfr2(+/P253R) neurocranium with an increase in phosphorylated p38 as well as ERK1/2, whereas phosphorylated AKT and PKCalpha were not obviously changed as compared to those of wild-type controls. There were localized phenotypic and molecular variations among individual embryos with different mutations and among those with the same mutation.ConclusionsOur in vivo studies demonstrated that the Fgfr2 +/P253R mutation resulted in mice with cranial features that resemble those of the Fgfr2(+/S252W) mice and human Apert syndrome. Activated p38 in addition to the ERK1/2 signaling pathways may mediate the mutant neurocranial phenotype. Though Apert syndrome is traditionally thought to be a consistent phenotype, our results suggest localized and regional variations in the phenotypes that characterize Apert syndrome.

Miller syndrome is an extremely rare condition in the group of facial dysostosis syndromes. These syndromes have great phenotypic overlap and variability, even within families. To facilitate the differentiation of Miller syndrome from related facial dysostosis syndromes, such as Treacher Collins and Nager syndrome, this study aims to provide an overview of the phenotypic spectrum of the syndrome. A systematic literature search of Embase, MEDLINE/PubMed, Web of Science, and CINAHL was conducted until November 2024. Case reports and case series of patients with a clinical or genetic diagnosis of Miller syndrome in all languages were included. The quality of the included reports was assessed using the Joanna Briggs Institute critical appraisal tool and the Fichas de Lectura Critica 3.0 web application. In total, 44 cases of Miller syndrome were found, with only 18.2% having genetic confirmation. Craniofacial anomalies were prominent, including midface hypoplasia (72.7%) and micrognathia (75.0%), orofacial clefts (77.3%), eyelid anomalies (70.5%), and external ear anomalies (63.6%). Limb anomalies were present in all cases, primarily involving the hands (95.5%), forearms (52.3%), and feet (90.9%). Anomalies in other extracraniofacial tracts were also reported. Despite limitations, including limited genetic confirmation and reliance on literature, this study provides valuable insights into the phenotypic spectrum of Miller syndrome. Efforts for genetic confirmation, international collaboration, and comprehensive reporting are essential to advance research and care for rare conditions like Miller syndrome. Therefore, a detailed checklist for phenotypic evaluation in Miller syndrome cases is provided in this study.