Rare genetic diseases impact many people worldwide and are challenging to diagnose. In this study, we introduce a novel regional population cohort approach to identify pathogenic variants causing Mendelian diseases that occur more frequently within specific populations and are of clinical interest for carrier testing. We utilized a cohort from Quebec, including the Saguenay–Lac-Saint-Jean region, which is known for its founder effect followed by a rapid expansion and higher frequency of certain pathogenic variants. By analyzing both their frequency and origin through shared identical-by-descent segments, we identified founder variants. We calculated and compared their frequency in individuals originating from the Saguenay–Lac-Saint-Jean and from other urban Quebec regions. We validated 38 previously reported variants as being more common due to the founder effect and population expansion. Additionally, we identified 42 unreported founder variants in Quebec or Saguenay–Lac-Saint-Jean, some with carrier rates estimates as high as 1/22. We also observed a greater deleterious mutational load for the studied variants in individuals from the Saguenay–Lac-Saint-Jean compared to other urban Quebec regions. These findings were brought to the clinic, where 12 pathogenic variants were detected in diagnosed patients. Five variants found in this study are responsible for very severe diseases and could be considered for inclusion in a carrier test for the Saguenay–Lac-Saint-Jean population. This study highlights the potential underestimation of rare disease prevalence and presents a population-based approach that could aid clinicians in their diagnostic efforts and patients’ management.

Rare genetic diseases impact many people worldwide and are challenging to diagnose. In this study, we introduce a novel regional population cohort approach to identify pathogenic variants causing Mendelian diseases that occur more frequently within specific populations and are of clinical interest for carrier testing. We utilized a cohort from Quebec, including the Saguenay-Lac-Saint-Jean region, which is known for its founder effect followed by a rapid expansion and higher frequency of certain pathogenic variants. By analyzing both their frequency and origin through shared identical-by-descent segments, we identified founder variants. We calculated and compared their frequency in individuals originating from the Saguenay-Lac-Saint-Jean and from other urban Quebec regions. We validated 38 previously reported variants as being more common due to the founder effect and population expansion. Additionally, we identified 42 unreported founder variants in Quebec or Saguenay-Lac-Saint-Jean, some with carrier rates estimates as high as 1/22. We also observed a greater deleterious mutational load for the studied variants in individuals from the Saguenay-Lac-Saint-Jean compared to other urban Quebec regions. These findings were brought to the clinic, where 12 pathogenic variants were detected in diagnosed patients. Five variants found in this study are responsible for very severe diseases and could be considered for inclusion in a carrier test for the Saguenay-Lac-Saint-Jean population. This study highlights the potential underestimation of rare disease prevalence and presents a population-based approach that could aid clinicians in their diagnostic efforts and patients' management.

Long-read sequencing (LRS) technologies have enhanced the ability to resolve complex genomic architecture and determine the ‘phase’ relationships of genetic variants over long distances. Although genome-wide association studies (GWAS) identify individual variants associated with complex traits, they do not typically account for whether multiple associated signals at a locus may act in cis or trans, or whether they reflect allelic heterogeneity. As a result, effects that arise specifically from phase relationships may remain hidden in analyses using short-read and microarray data. While the advent of LRS has enabled accurate measurement of phase in population cohorts, statistical methods that leverage phase in genetic association analysis remain underdeveloped. Here, we introduce the Regression on Phase (RoP) method, which directly models cis and trans phase effects between variants under a regression framework. In simulations, RoP outperforms genotype interaction tests that detect phase effects indirectly, and distinguishes in-cis from in-trans phase effects. We implemented RoP at two cystic fibrosis (CF) modifier loci discovered by GWAS. At the chromosome 7q35 trypsinogen locus, RoP confirmed that two variants contributed independently (allelic heterogeneity). At the SLC6A14 locus on chromosome X, phase analysis uncovered a coordinated regulatory mechanism in which a promoter variant modulates lung phenotypes in individuals with CF when acting in cis with a lung-specific enhancer (E2765449/enhD). This coordinated regulation was confirmed in functional studies. These findings highlight the potential of leveraging phase information from LRS in genetic association studies. Analyzing phase effects with RoP can provide deeper insights into the complex genetic architectures underlying disease phenotypes, ultimately guiding more informed functional investigations and potentially revealing new therapeutic targets.

Electroretinography (ERG) provides a noninvasive functional measure of multiple cell types of the outer retina. We conducted an ERG-based screen of 530 single-gene knockout mouse strains generated as part of the International Mouse Phenotyping Consortium, representing 2.5% of all protein-coding genes, to identify genetic variants affecting retinal function. We identified 30 strains with significantly altered ERG amplitudes. Two of the genes identified, Cfap418 and Syne2, have been previously reported with outer retinal dysfunction, thereby serving as internal controls that validate our screening protocol. Of the remaining 28 genes newly associated with altered retinal function, the majority lacked a contemporaneous histopathology correlate, highlighting the importance of ERG in early detection of functional abnormalities. A rare homozygous missense variant in FCHSD2, the human orthologue of one of the 28 genes identified, was found in a patient presenting with retinal degeneration that lacked a molecular diagnosis. This report represents a useful resource for future investigations into the molecular mechanisms driving inherited retinal diseases and demonstrates the power of large-scale ERG screening in identifying novel genetic determinants of retinal function.

Interactions between risk factors and covariate-defined groups are commonly observed in complex diseases. Existing methods for detecting interactions typically require individual-level data. The data availability and the measurements of risk exposures and covariates often limit the power and applicability in assessing interactions. To address these limitations, we propose int2MR, an integrative Mendelian randomization (MR) method that leverages GWAS summary statistics on exposure traits and group-separated and/or combined GWAS statistics on outcome traits. The int2MR can assess a broad range of risk exposure effects on diseases and traits, revealing interactions unattainable with incomplete or limited individual-level data. Simulation studies demonstrate that int2MR effectively controls type I error rates under various settings while achieving considerable power gains with the integration of additional group-combined GWAS data. We applied int2MR to two data analyses. First, we identified risk exposures with sex-interaction effects on ADHD, and our results suggested potentially elevated inflammation in males. Second, we detected age-group-specific risk factors for Alzheimer’s disease pathologies in the oldest-old (age 95+); many of these factors were related to immune and inflammatory processes. Our findings suggest that reduced chronic inflammation may underlie the distinct pathological mechanisms observed in this age group. The int2MR is a robust and flexible tool for assessing group-specific or interaction effects, providing insights into disease mechanisms.

Precise, monoallelic expression of imprinted genes is governed by cis regulatory elements called imprinting control regions (ICRs) and enhancer-promoter (E-P) interactions shaped by local chromatin architecture. The Igf2/H19 locus employs allele-specific CTCF binding at the ICR to instruct enhancer accessibility to maternal H19 and paternal Igf2 promoters. Here, we investigate the CTCF-bound centrally conserved domain (CCD), intergenic to H19 and Igf2, and an adjacent widely expressed lncRNA. Using transgenic mice, deletion alleles reinforced CCD as a neonatal muscle-specific repressor of maternal Igf2. However, deletion of the abutting lncRNA did not affect Igf2 levels. Unexpectedly, in adult skeletal muscle where Igf2 is normally repressed, absence of CCD resulted in remarkable, high-level activation of Igf2 from both parental alleles. Through multimodal chromatin analyses, we identified a conserved putative adult skeletal muscle enhancer (PaSME) insulated between chromatin domains at ICR and CCD. We propose that removal of CCD allows PaSME to drive robust abnormal Igf2 activation on both alleles in adult skeletal muscle. Thus, we uncover CCD as a developmental biallelic muscle-specific repressor, adding a new layer of architectural regulation to the extensively studied Igf2/H19 locus.

As rapidly growing bacteria begin to exhaust nutrients, their growth rate slows, ultimately leading to the non-replicative state of quiescence. Adaptation to nutrient limitation requires widespread metabolic remodeling that is in part mediated by the phosphorylated nucleotides guanosine tetra- and penta-phosphate, collectively (p)ppGpp. We have developed a novel reporter of (p)ppGpp abundance in the Gram-positive bacterium Bacillus subtilis based on the recent identification of a riboswitch that binds (p)ppGpp and modulates transcription via regulation of a transcriptional terminator. Placement of an unstable reporter, firefly luciferase, downstream of the riboswitch allows for sensitive and dynamic assessment of (p)ppGpp. We first confirm that the reporter accurately reflects (p)ppGpp abundance in a variety of well-established conditions. We then proceed to use it to demonstrate the physiological importance of several mechanisms of regulation of (p)ppGpp metabolism previously observed only in vitro including allosteric interactions between (p)ppGpp synthesis enzymes and the hydrolytic activity of a (p)ppGpp synthetase. (p)ppGpp signaling has been implicated in the regulation of gene expression, and we demonstrate a close temporal association between gene expression and (p)ppGpp abundance, indicating a rapid, and therefore likely direct mechanism of (p)ppGpp dependent gene activation. Thus, this reporter provides a new, comprehensive analysis of (p)ppGpp signaling in vivo and offers the potential ability to sensitively monitor the temporal dynamics of (p)ppGpp abundance under diverse environmental conditions.

Neuromodulators and peptide hormones play important roles in regulating animal behavior. A well-studied example is ecdysis, which is used by insects to shed their exoskeleton at the end of each molt. Ecdysis is initiated by Ecdysis Triggering Hormone (ETH) and Eclosion Hormone (EH), which interact via positive feedback to coordinate the sequence of behavioral and physiological changes that cause exoskeleton shedding. Whereas the cell types targeted by ETH are well characterized, those targeted by EH have remained largely unknown due to limited characterization of the EH receptor (EHR). A gene encoding an EHR has been described in the oriental fruit fly, B. dorsalis, and in the desert locust, Schistocerca gregaria. However, little is known in these species about its expression pattern and its precise role at ecdysis, and no other insect EHRs are known. Here we analyze CG10738, the Drosophila ortholog of the B. dorsalis gene encoding EHR, and show that expressing it in cells confers sensitivity to EH. In addition, mutations of CG10738 specifically disrupt ecdysis, phenocopying the knockout of the EH gene. Together, these results indicate that CG10738 encodes the Drosophila EHR. As in B. dorsalis, EHR is expressed in the ETH-producing Inka cells; in addition, it is expressed in many known targets of ETH, including the neurons responsible for the secretion of other ecdysis-related peptides, such as CCAP and EH itself. Our results from targeted knockdown and rescue experiments reveal that EHR is required for ecdysis in diverse cell types and that the role of EHR in different targets differs with developmental stage. Our findings indicate extensive convergence of EH and ETH signaling and provide an exemplar of the complex mechanisms by which hormones control animal behavior.

The T-type voltage-gated calcium channel CaV3.3 is expressed in GABAergic neurons of the thalamic reticular nucleus (TRN), where its pacemaking activity controls sleep spindle rhythmogenesis during the non-rapid eye movement (NREM) phase of natural sleep. Previously, we established CACNA1I, the gene coding for CaV3.3, as a disease gene for neurodevelopmental disease with or without epilepsy. Here we report three newly identified activation-gate-modifying heterozygous missense variants of CACNA1I, found in four unrelated patients with neurodevelopmental disease with or without seizures. One of these variants, p.(Met1425Val), is an amino-acid substitution at the same position as previously published variant p.(Met1425Ile). Notably, the other two variants studied here are also a pair of two different substitutions of the same amino acid: p.(Ala398Val) and p.(Ala398Glu). By using site-directed mutagenesis, voltage-clamp electrophysiology, computational modelling of neuronal excitability, and structure modelling, we found that the two substitutions of M1425 both result in a gain of channel function including left-shifted voltage-dependence of activation and inactivation, slowed inactivation and deactivation kinetics, and increased neuronal excitability. Remarkably, the two substitutions of A398 show opposite effects on channel function. While substitution A398E leads to a gain of channel function, A398V results in decreased current density, accelerated gating kinetics, and a decreased neuronal excitability. The lack of seizures in the two independent p.(Ala398Val) patients correlates with the absence of increased neuronal excitability in this variant. This is the first report of a gate-modifying CaV3.3 channel variant with partial loss-of-function effects associated with developmental delay and intellectual disability without seizures. Our study corroborates the role of CaV3.3 dysfunction in the etiology of neurodevelopmental disorders. Moreover, our data suggest that substantial gain-of-function of CaV3.3 leads to the development of seizures, whereas both gain- and loss-of-function variants of CACNA1I can cause neurodevelopmental disease.

PHYTOCHROME INTERACTING FACTOR 4 (PIF4) is a vital transcription factor that controls plant growth by integrating environmental signals like light and temperature. Recent studies have shown many upstream regulators, such as HEMERA (HMR), HEAT SHOCK TRANSCRIPTION FACTORS (HSFs), TEOSINTE BRANCHED 1/CYCLOIDEA/PCF 5 (TCP5), and the B-BOX (BBX) proteins, play roles in regulating PIF4 transcription. However, the role of PIF4 in controlling its own gene expression is unknown. Here, we demonstrate that the PIF4 undergoes negative autoregulation. We show that PIF4 promoter activity is higher in the pif4 mutant but significantly reduced in PIF4 overexpression transgenic lines. Moreover, CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) enhances PIF4 protein stability and promotes PIF4 autoinhibition. However, Phytochrome B (phyB), a photoreceptor that decreases PIF4 stability, inhibits autoinhibition. We further develop a network-based mathematical model incorporating the PIF4 autoinhibition and other key interactions. Our modeling and data analysis reveal that PIF4 autoregulation depends on a threshold of cellular PIF4 concentration. Our model also successfully predicts the hypocotyl growth and PIF4 promoter activity in various light and temperature conditions. Moreover, we show that the transgenic lines with enhanced PIF4 function negatively influence biomass and yield, irrespective of photoperiod and temperature. Together, the negative feedback of PIF4 dampens its own function and restrains unregulated growth. Our study thus elucidates the mechanisms of how the phyB-COP1/DET1-PIF4 module controls PIF4 transcription in tune with the endogenous PIF4 level.