Hyperactivation of RAS/MAPK signaling is a hallmark of RASopathies, genetic developmental conditions associated with cognitive and sensory processing impairments. Genes linked to this pathway have been reported to be enriched among Drosophila models with habituation deficits, a behavioral phenotype reflecting impaired sensory filtering. To investigate whether RAS/MAPK overactivation extends beyond classical RASopathies, we generated 89 and screened 41 viable habituation deficient Drosophila RNAi models, measuring pathway activity as an increased phosphorylated ERK to ERK ratio. This screen identified Sms, the ortholog of human spermine synthase (SMS), implicated in Snyder-Robinson syndrome. RAS/MAPK overactivation along with hyperreactivity and habituation impairments were confirmed in a full loss-of-function mutant. An RNAi screen targeting polyamine pathway genes identified Sat (human SAT1/2, SATL1), with independent models reproducing aspects of these phenotypes. Knockdown of Sms or Sat in GABAergic neurons impaired habituation, suggesting a role for polyamine metabolism in inhibitory circuit function. These findings reveal previously unrecognized convergence between polyamine dysregulation and RASopathies, raising the possibility for shared therapeutic opportunities through modulation of either pathway.
Background /Objectives: The fetal thymus is increasingly assessed as a marker of fetal wellbeing, yet reliable gestational-age-specific reference data remain limited. We aimed to establish reference ranges, centile charts, and internally validated Z-score equations for the thymus transverse diameter at 18 + 0-25 + 6 weeks of gestation. Methods: This retrospective cross-sectional study was conducted at a single tertiary fetal medicine centre between January 2023 and December 2025. Structurally normal singleton pregnancies with a reliable gestational age were eligible. The maximum transverse diameter of the fetal thymus was measured in the three-vessel trachea view. The mean was modelled by polynomial regression and, after heteroscedasticity was confirmed, a gestational-age-specific standard deviation was modelled using the Royston-Wright approach. Z-score equations and smoothed centiles were derived, and performance was assessed by bootstrap, cross-validation, and split-sample validation. Results: A total of 2103 pregnancies were included. A cubic mean model was selected, and variance increased significantly with gestation (Breusch-Pagan p = 1.34 & times; 10-18). The predicted median increased from 9.7 mm at 18 weeks to 18.3 mm at 25 weeks. Fetal sex was statistically associated with thymus transverse diameter, but the effect was negligible (adjusted mean difference 0.247 mm; p = 0.011; Cohen's d = 0.051; interaction p = 0.949), so a single reference was retained. Excluding maternal comorbidities changed the median by at most 0.24 mm. Bootstrap optimism was 0.006 mm and the 10-fold cross-validated root-mean-square error 1.863 mm. Conclusions: We provide contemporary gestational-age-specific reference ranges and internally validated Z-score equations for the thymus transverse diameter between 18 + 0 and 25 + 6 weeks, which may support clinical assessment and future research, pending external validation.
ABSTRACT Genomic newborn and population screening is rapidly moving from pilot to policy. England's Generation Study has already enrolled tens of thousands of babies, and NHS England has committed to offering whole-genome sequencing to every newborn within a decade. Several such international initiatives, from programmes in Massachusetts and New York to Guangdong, are rapidly expanding gene panels. This expansion, however, is associated with a growing risk of over-calling genomic variants in asymptomatic infants, for whom traditional phenotype-first diagnostic models no longer apply. Osteogenesis imperfecta (OI) provides an instructive test case. It has been long treated as a textbook example of a highly penetrant Mendelian disease; however, population-scale data now show that a substantial proportion of adults carrying ‘pathogenic’ COL1A1/COL1A2 variants have no recorded clinical diagnosis of OI. Using OI as an exemplar, this article explores what genomic screening programmes can realistically deliver, identifies other conditions sharing this penetrance gap, and outlines how programmes can expand without eroding public trust.
The propagation of pathological proteins such as tau and amyloid-beta (Aβ) in Alzheimer's disease (AD) is poorly understood. Here, we developed a human-relevant in vitro conditioned medium (CM)-based model using human neural progenitor ReN cells carrying Familial AD (FAD) mutations in amyloid precursor protein (APP Sw/Lo) and presenilin 1 (PSEN1ΔE9). Healthy ReN-derived neurons and astrocytes treated with FAD-CM for nine weeks exhibited AD features, including cellular toxicity, neuro-glial alterations, and mitochondrial dysfunction. Exogenous Aβ42 further induced neuroglial and mitochondrial damage. Exosomes released by FAD cells and -to a lesser extent- by CM-treated healthy cells showed elevated Aβ42/40 ratios. Proteomic analysis also revealed that exosomes from FAD-cells carried a distinct content, including overrepresentation of proteins linked to inflammation, extracellular matrix remodelling, synaptic dysfunction, and Aβ processing, as well as Calmodulin-like protein 3. Moreover, exosomes were actively internalized by healthy cells through an actin-dependent mechanism. In summary, these findings support a model based on FAD-associated APP/PSEN1 mutations in which exosome-associated cargo alongside soluble and non-vesicular factors contribute to the transfer of AD-associated cellular phenotypes.
Claudin-4 (CLDN4) is a tight junction protein that contributes to epithelial barrier function and regulation of paracellular ion permeability in the distal nephron. Although CLDN4 dysfunction has been linked to tubular transport abnormalities, its role in calcium handling and kidney stone disease remains unclear. We examined the molecular and functional effects of a kidney stone–associated CLDN4 variant, P74L, using doxycycline-inducible epithelial cell models expressing human wild-type (WT) or P74L CLDN4. Compared with WT CLDN4, the P74L variant displayed reduced protein stability, impaired junctional incorporation, and decreased surface expression. In contrast with WT CLDN4, whose overexpression increased transepithelial electrical resistance and restricted paracellular sodium, chloride, and calcium permeability, P74L CLDN4 failed to confer these effects. Expression of P74L CLDN4 was associated with reduced CLDN3 and CLDN7 protein abundance without significant changes in CLDN8 or transcriptional regulation of other distal ion transport genes. Together, these findings identify CLDN4 P74L as a loss-of-function variant that compromises epithelial barrier function and fails to restrict paracellular calcium permeability, possibly leading to altered calcium handling relevant to nephrolithiasis.
