APOE4/4 is linked to damaging lipid droplets in Alzheimer's disease microglia.

Several genetic risk factors for Alzheimer's disease implicate genes involved in lipid metabolism and many of these lipid genes are highly expressed in glial cells1. However, the relationship between lipid metabolism in glia and Alzheimer's disease pathology remains poorly understood. Through single-nucleus RNA sequencing of brain tissue in Alzheimer's disease, we have identified a microglial state defined by the expression of the lipid droplet-associated enzyme ACSL1 with ACSL1-positive microglia being most abundant in patients with Alzheimer's disease having the APOE4/4 genotype. In human induced pluripotent stem cell-derived microglia, fibrillar Aß induces ACSL1 expression, triglyceride synthesis and lipid droplet accumulation in an APOE-dependent manner. Additionally, conditioned media from lipid droplet-containing microglia lead to Tau phosphorylation and neurotoxicity in an APOE-dependent manner. Our findings suggest a link between genetic risk factors for Alzheimer's disease with microglial lipid droplet accumulation and neurotoxic microglia-derived factors, potentially providing therapeutic strategies for Alzheimer's disease.

Organ aging signatures in the plasma proteome track health and disease.

Animal studies show aging varies between individuals as well as between organs within an individual1-4, but whether this is true in humans and its effect on age-related diseases is unknown. We utilized levels of human blood plasma proteins originating from specific organs to measure organ-specific aging differences in living individuals. Using machine learning models, we analysed aging in 11 major organs and estimated organ age reproducibly in five independent cohorts encompassing 5,676 adults across the human lifespan. We discovered nearly 20% of the population show strongly accelerated age in one organ and 1.7% are multi-organ agers. Accelerated organ aging confers 20-50% higher mortality risk, and organ-specific diseases relate to faster aging of those organs. We find individuals with accelerated heart aging have a 250% increased heart failure risk and accelerated brain and vascular aging predict Alzheimer's disease (AD) progression independently from and as strongly as plasma pTau-181 (ref. 5), the current best blood-based biomarker for AD. Our models link vascular calcification, extracellular matrix alterations and synaptic protein shedding to early cognitive decline. We introduce a simple and interpretable method to study organ aging using plasma proteomics data, predicting diseases and aging effects.

Young CSF restores oligodendrogenesis and memory in aged mice via Fgf17.

Recent understanding of how the systemic environment shapes the brain throughout life has led to numerous intervention strategies to slow brain ageing1-3. Cerebrospinal fluid (CSF) makes up the immediate environment of brain cells, providing them with nourishing compounds4,5. We discovered that infusing young CSF directly into aged brains improves memory function. Unbiased transcriptome analysis of the hippocampus identified oligodendrocytes to be most responsive to this rejuvenated CSF environment. We further showed that young CSF boosts oligodendrocyte progenitor cell (OPC) proliferation and differentiation in the aged hippocampus and in primary OPC cultures. Using SLAMseq to metabolically label nascent mRNA, we identified serum response factor (SRF), a transcription factor that drives actin cytoskeleton rearrangement, as a mediator of OPC proliferation following exposure to young CSF. With age, SRF expression decreases in hippocampal OPCs, and the pathway is induced by acute injection with young CSF. We screened for potential SRF activators in CSF and found that fibroblast growth factor 17 (Fgf17) infusion is sufficient to induce OPC proliferation and long-term memory consolidation in aged mice while Fgf17 blockade impairs cognition in young mice. These findings demonstrate the rejuvenating power of young CSF and identify Fgf17 as a key target to restore oligodendrocyte function in the ageing brain.

CD22 blockade restores homeostatic microglial phagocytosis in ageing brains.

Microglia maintain homeostasis in the central nervous system through phagocytic clearance of protein aggregates and cellular debris. This function deteriorates during ageing and neurodegenerative disease, concomitant with cognitive decline. However, the mechanisms of impaired microglial homeostatic function and the cognitive effects of restoring this function remain unknown. We combined CRISPR-Cas9 knockout screens with RNA sequencing analysis to discover age-related genetic modifiers of microglial phagocytosis. These screens identified CD22, a canonical B cell receptor, as a negative regulator of phagocytosis that is upregulated on aged microglia. CD22 mediates the anti-phagocytic effect of α2,6-linked sialic acid, and inhibition of CD22 promotes the clearance of myelin debris, amyloid-ß oligomers and α-synuclein fibrils in vivo. Long-term central nervous system delivery of an antibody that blocks CD22 function reprograms microglia towards a homeostatic transcriptional state and improves cognitive function in aged mice. These findings elucidate a mechanism of age-related microglial impairment and a strategy to restore homeostasis in the ageing brain.

Small molecule C381 targets the lysosome to reduce inflammation and ameliorate disease in models of neurodegeneration.

SignificanceNeurodegenerative diseases are poorly understood and difficult to treat. One common hallmark is lysosomal dysfunction leading to the accumulation of aggregates and other undegradable materials, which cause damage to brain resident cells. Lysosomes are acidic organelles responsible for breaking down biomolecules and recycling their constitutive parts. In this work, we find that the antiinflammatory and neuroprotective compound, discovered via a phenotypic screen, imparts its beneficial effects by targeting the lysosome and restoring its function. This is established using a genome-wide CRISPRi target identification screen and then confirmed using a variety of lysosome-targeted studies. The resulting small molecule from this study represents a potential treatment for neurodegenerative diseases as well as a research tool for the study of lysosomes in disease.

Cerebral Blood Flow Assessed with Phase-contrast Magnetic Resonance Imaging during Blood Pressure Changes with Noradrenaline and Labetalol: A Trial in Healthy Volunteers.

BACKGROUND: Adequate cerebral perfusion is central during general anesthesia. However, perfusion is not readily measured bedside. Clinicians currently rely mainly on mean arterial pressure (MAP) as a surrogate, even though the relationship between blood pressure and cerebral blood flow is not well understood. The aim of this study was to apply phase-contrast magnetic resonance imaging to characterize blood flow responses in healthy volunteers to commonly used pharmacologic agents that increase or decrease arterial blood pressure. METHODS: Eighteen healthy volunteers aged 30 to 50 yr were investigated with phase-contrast magnetic resonance imaging. Intra-arterial blood pressure monitoring was used. First, intravenous noradrenaline was administered to a target MAP of 20% above baseline. After a wash-out period, intravenous labetalol was given to a target MAP of 15% below baseline. Cerebral blood flow was measured using phase-contrast magnetic resonance imaging and defined as the sum of flow in the internal carotid arteries and vertebral arteries. Cardiac output (CO) was defined as the flow in the ascending aorta. RESULTS: Baseline median cerebral blood flow was 772 ml/min (interquartile range, 674 to 871), and CO was 5,874 ml/min (5,199 to 6,355). The median dose of noradrenaline was 0.17 µg · kg-1 · h-1 (0.14 to 0.22). During noradrenaline infusion, cerebral blood flow decreased to 705 ml/min (606 to 748; P = 0.001), and CO decreased to 4,995 ml/min (4,705 to 5,635; P = 0.01). A median dose of labetalol was 120 mg (118 to 150). After labetalol boluses, cerebral blood flow was unchanged at 769 ml/min (734 to 900; P = 0.68). CO increased to 6,413 ml/min (6,056 to 7,464; P = 0.03). CONCLUSIONS: In healthy, awake subjects, increasing MAP using intravenous noradrenaline decreased cerebral blood flow and CO. These data do not support inducing hypertension with noradrenaline to increase cerebral blood flow. Cerebral blood flow was unchanged when decreasing MAP using labetalol.

Perioperative patient safety indicators-A Delphi study.

AIM: To identify, define and achieve consensus on perioperative patient safety indicators within a Swedish context. DESIGN: A modified Delphi method. METHODS: A purposeful sample of 22 experts, all experienced operating room nurse specialists, was recruited for this study. A questionnaire was constructed incorporating statements derived from a preceding study. The experts were asked to rate the importance of each statement concerning patient safety during the perioperative phase. The data collection occurred through an online survey platform between November 2022 and April 2023. The CREDES checklist guided the reporting of this study. RESULTS: The three-round Delphi study resulted in consensus on 73 statements out of 103, encompassing 74% process indicators and 26% structure indicators. Key areas of consensus included the use of the Surgical Safety Checklist and optimizing the operating room environment. CONCLUSION: Consensus was reached on perioperative safety indicators, underscoring the intricate challenges involved in ensuring patient safety in the operating room. It emphasizes the important integration of both structure and process indicators for comprehensive safety assessment during surgical procedures. Recognizing the difficulty in measuring factors like teamwork and communication, essential for patient safety, the study offers practical guidance. It underlines a balanced approach and specific consensus areas applicable in clinical practice to enhance perioperative patient safety. IMPLICATIONS FOR THE PROFESSION AND PATIENT CARE: This study provides concrete practice guidance and establishes a structured framework for evaluating perioperative care processes. It emphasizes the critical role of professionals having the necessary skills and being present during surgical procedures. Additionally, the study underscores the paramount importance of effective communication and teamwork within the operating room team, substantively contributing to overall patient safety enhancement. IMPACT: The study focused on addressing the challenge of ensuring patient safety in operating rooms, acknowledging the persistent complications related to surgery despite global efforts to eliminate avoidable harm in healthcare. Consensus was reached on 73 crucial indicators for perioperative patient safety, emphasizing a balanced approach integrating both process and structure indicators for a comprehensive assessment of safety during surgical procedures. The study has a broad impact on professionals and healthcare systems, providing concrete guidance for practice and offering a structured process for evaluating perioperative care. REPORTING METHOD: The study is reported informed by 'Guidance on Conducting and REporting DElphi Studies (CREDES) in palliative care: Recommendations derived from a methodological systematic review'. PATIENT OR PUBLIC CONTRIBUTION: No patient or public contribution.

Effects of an advanced first aid course or real-time video communication with ambulance personnel on layperson first response for building-site severe injury events: a simulation study.

BACKGROUND: The risk of high-energy trauma injuries on construction sites is relatively high. A delayed response time could affect outcomes after severe injury. This study assessed if an advanced first aid course for first aid response for laypersons (employees or apprentices) in the construction industry or real-time video communication and support with ambulance personnel, or neither, together with access to an advanced medical kit, would have an effect on immediate layperson vital responses in a severe injury scenario. METHOD: This was a controlled simulation study. Employees or apprentices at a construction site were recruited and randomly allocated into a group with video support or not, and advanced first aid course or not, and where one group had both. The primary outcomes were correct behavior to recognize and manage an occluded airway and correct behavior to stop life-threatening bleeding from a lower extremity injury. Secondary outcomes included head-to-toe assessment performed, placement of a pelvic sling, and application of remote vital signs monitors. RESULTS: Ninety participants were included in 10 groups of 3 for each of 4 exposures. One group was tested first as a baseline group, and then later after having done the training course. Live video support was effective in controlling bleeding. A first aid course given beforehand did not seem to be as effective on controlling bleeding. Video support and the first aid course previously given improved the ability of bystanders to manage the airway, the combination of the two being no better than each of the interventions taken in isolation. Course exposure and video support together were not superior to the course by itself or video by itself, except regarding placing the biosensors on the injured after video support. Secondary results showed an association between video support and completing a head-to-toe assessment. Both interventions were associated with applying a pelvic sling. CONCLUSION: These findings show that laypersons, here construction industry employees, can be supported to achieve good performance as first responders in a major injury scenario. Prior training, but especially live video support without prior training, improves layperson performance in this setting.

Preoperative anxiety level is not associated with postoperative negative behavioral changes in premedicated children.

BACKGROUND: Anesthesia preinduction anxiety in children can according to some studies lead to long-term anxiety and negative behavioral changes (NBC), while other studies have not found this effect. This secondary analysis from a recent premedication trial comparing clonidine and midazolam aimed to test the relation between preoperative anxiety assessed with modified Yale Preoperative Anxiety Scale (mYPAS) and postoperative NBCs assessed with Post Hospital Behavior Questionnaire (PHBQ), regardless of premedication type. METHODS: This is a planned secondary analysis from a published premedication comparison trial in an outpatient surgery cohort, children aged 2-7 years. Participant and preoperative factors, particularly preoperative anxiety as mYPAS scores, were assessed for association with development of postoperative NBCs. RESULTS: Fifty-four of the 115 participants had high preinduction anxiety (mYPAS >30), and 19 of 115 developed >3 postoperative NBCs 1 week after surgery. There was no association between preinduction anxiety level as mYPAS scores and the development of postoperative NBCs at 1 week after surgery (10 of 19 had both, p = .62) nor after 4- or 26-weeks post-surgery. Only lower age was associated with development of NBCs postoperatively. CONCLUSIONS: Based on the findings from this cohort, high preinduction anxiety does not appear to be associated with NBCs postoperatively in children premedicated with clonidine or midazolam.

Surface microdialysis measures local tissue metabolism after Ivor Lewis esophagectomy; an attempt to predict anastomotic defect.

Anastomotic defect (AD) after esophagectomy can lead to severe complications with need for surgical or endoscopic intervention. Early detection enables early treatment and can limit the consequences of the AD. As of today, there are limited methods to predict AD. In this study, we have used microdialysis (MD) to measure local metabolism at the intrathoracic anastomosis. Feasibility and possible diagnostic use were investigated. Sixty patients planned for Ivor Lewis esophagectomy were enrolled. After construction of the anastomosis, surface MD (S-MD) probes were attached to the outer surface of the esophageal remnant and the gastric conduit in close vicinity of the anastomosis and left in place for 7 postoperative days (PODs). Continuous sampling of local tissue concentrations of metabolic substances (glucose, lactate, and pyruvate) was performed postoperatively. Outcome, defined as AD or not according to Esophagectomy Complications Consensus Group definitions, was recorded at discharge or at first postoperative follow up. Difference in concentrations of metabolic substances was analyzed retrospectively between the two groups by means of artificial neural network technique. S-MD probes can be attached and removed from the gastric tube reconstruction without any adverse events. Deviating metabolite concentrations on POD 1 were associated with later development of AD. In subjects who developed AD, no difference in metabolic concentrations between the esophageal and the gastric probe was recorded. The technical failure rate of the MD probes/procedure was high. S-MD can be used in a clinical setting after Ivor Lewis esophagectomy. Deviation in local tissue metabolism on POD 1 seems to be associated with development of AD. Further development of MD probes and procedure is required to reduce technical failure.

Comprehensive, integrated, and phased whole-genome analysis of the primary ENCODE cell line K562.

K562 is widely used in biomedical research. It is one of three tier-one cell lines of ENCODE and also most commonly used for large-scale CRISPR/Cas9 screens. Although its functional genomic and epigenomic characteristics have been extensively studied, its genome sequence and genomic structural features have never been comprehensively analyzed. Such information is essential for the correct interpretation and understanding of the vast troves of existing functional genomics and epigenomics data for K562. We performed and integrated deep-coverage whole-genome (short-insert), mate-pair, and linked-read sequencing as well as karyotyping and array CGH analysis to identify a wide spectrum of genome characteristics in K562: copy numbers (CN) of aneuploid chromosome segments at high-resolution, SNVs and indels (both corrected for CN in aneuploid regions), loss of heterozygosity, megabase-scale phased haplotypes often spanning entire chromosome arms, structural variants (SVs), including small and large-scale complex SVs and nonreference retrotransposon insertions. Many SVs were phased, assembled, and experimentally validated. We identified multiple allele-specific deletions and duplications within the tumor suppressor gene FHIT Taking aneuploidy into account, we reanalyzed K562 RNA-seq and whole-genome bisulfite sequencing data for allele-specific expression and allele-specific DNA methylation. We also show examples of how deeper insights into regulatory complexity are gained by integrating genomic variant information and structural context with functional genomics and epigenomics data. Furthermore, using K562 haplotype information, we produced an allele-specific CRISPR targeting map. This comprehensive whole-genome analysis serves as a resource for future studies that utilize K562 as well as a framework for the analysis of other cancer genomes.

Plasma and bronchoalveolar lavage fluid oxylipin levels in experimental porcine lung injury.

Inflammatory signaling pathways involving eicosanoids and other regulatory lipid mediators are a subject of intensive study, and a role for these in acute lung injury is not yet well understood. We hypothesized that oxylipin release from lung injury could be detected in bronchoalveolar lavage fluid and in plasma. In a porcine model of surfactant depletion, ventilation with hyperinflation was assessed. Bronchoalveolar lavage and plasma samples were analyzed for 37 different fatty acid metabolites (oxylipins). Over time, hyperinflation altered concentrations of 4 oxylipins in plasma (TXB2, PGE2, 15-HETE and 11-HETE), and 9 oxylipins in bronchoalveolar lavage fluid (PGF2α, PGE2, PGD2, 12,13-DiHOME, 11,12-DiHETrE, 13-HODE, 9-HODE, 15-HETE, 11-HETE). Acute lung injury caused by high tidal volume ventilation in this porcine model was associated with rapid changes in some elements of the oxylipin profile, detectable in lavage fluid, and plasma. These oxylipins may be relevant in the pathogenesis of acute lung injury by hyperinflation.

Clonidine Versus Midazolam Premedication and Postoperative Negative Behavioral Changes in Younger Children: A Randomized Controlled Trial.

BACKGROUND: Postoperative negative behavioral changes (NBCs) are common among children, but risk for this is thought to be reduced with premedication. Midazolam has for many years been a standard premedication for children. More recently, the alpha-2 adrenergic agonist clonidine has also become popular as a preanesthetic sedative. We hypothesized that clonidine was superior to midazolam for limiting new NBCs in children as assessed using the Post Hospital Behavior Questionnaire (PHBQ). METHODS: This was a prospective, randomized, controlled, blinded study, including 115 participants aged 24 to 95 months and their parents. The participants underwent ear, nose, or throat outpatient surgery and were randomly allocated to premedication with oral midazolam 0.5 mg/kg or oral clonidine 4 µg/kg. Participants were anesthetized by protocol. At home, later, parents were asked to complete the PHBQ assessment instrument for postoperative NBCs for the participants 1 week, 1 month, and 6 months after the surgery. A secondary outcome, preinduction anxiety, was assessed using modified Yale Preoperative Anxiety Scale (mYPAS). RESULTS: The primary outcome, more than 3 NBCs in an individual case at 1 week, showed no difference in proportions between treatment in the clonidine group compared to the midazolam group, (12/59 or 20% vs 7/56 or 13%, respectively, odds ratio 1.39, 95% confidence interval [CI], 0.75-2.58; P = .32). A secondary result showed a higher preinduction anxiety level in the clonidine compared to the midazolam group (mYPAS >30, 43/59 or 71% vs 12/56 or 21%, respectively; P < .001). CONCLUSIONS: These results did not show a clinical or statistically significant difference, with respect to the primary outcome of behavior changes at 1 week, between the cohorts that received midazolam versus clonidine as a premedication.

Left atrial contraction strain and controlled preload alterations, a study in healthy individuals.

BACKGROUND: In order to assess left atrial contractile function in disturbed circulatory conditions, it is necessary to have a clear understanding of how it behaves in a normal resting state with changes in loading conditions. However, currently the understanding of this relationship is incomplete. We hypothesize that in healthy individuals, left atrial contraction strain and its peak strain rate are increased or decreased by increasing or decreasing preload, respectively. METHODS: Controlled maneuvers used to change preload included continuous positive airway pressure by mask (CPAP 20 cmH2O) for preload decrease, and passive leg raise (15 degrees angle) for preload increase. Cardiac ultrasound 4-chamber views of the left atria and left ventricle were acquired at baseline and during maneuver. Acquired images were post processed and analyzed offline. Comparisons were made using paired t-test and means with 95% confidence interval. RESULTS: There were 38 participants, complete results were obtained from 23 in the CPAP maneuver and 27 in the passive leg raise maneuver. For the CPAP group, left atrial contraction strain was 11.6% (10.1 to 13.1) at baseline and 12.8% (11.0 to 14.6) during the maneuver (p = 0.16). Left atrial contraction peak strain rate was - 1.7 s- 1 (- 1.8 to - 1.5) at baseline and - 1.8 s- 1 (- 2.0 to - 1.6) during the maneuver (p = 0.29). For the passive leg raise-group, left atrial contraction strain was 10.1% (9.0 to 11.2) at baseline and 10.8% (9.4 to 12.3) during the maneuver (p = 0.28). Left atrial contraction peak strain rate was - 1.5 s- 1 (- 1.6 to - 1.4) at baseline and - 1.6 s- 1 (- 1.8 to - 1.5) during the maneuver (p = 0.29). Left atrial area, an indicator of preload, increased significantly during passive leg raise and decreased during CPAP. CONCLUSION: In healthy individuals, left atrial contraction strain and its peak strain rate seem to be preload-independent. TRIAL REGISTRATION: The study was 2018-02-19 registered at clinicaltrials.gov ( NCT03436030 ).

Total Mission Time and Mortality in a Regional Interhospital Critical Care Transport System: A Retrospective Observational Study.

OBJECTIVE: We assessed the mortality risk related to the time for intensive care unit transport in a geographically large regional health care system. METHODS: Patient-level data from critical care ambulance missions were analyzed for 2,067 cases, mission time, and relevant patient factors. Mission time was used as a surrogate for the "distance" to tertiary care, and mortality at 7 days and other intervals was assessed. RESULTS: No increased mortality risk was found at 7 days in an unadjusted regression analysis (odds ratio = 1.00; range, 0.999-1.002; P = .66). In a secondary analysis, an increased mortality risk was observed in longer mission time subgroups and at later mortality assessment intervals (> 375 mission minutes and 90-day mortality; adjusted hazard ratio = 1.56; range, 1.07-2.28; P = .02). Negative changes in oxygenation and hemodynamic status and transport-related adverse events were associated with the longest flight times. Measurable but small changes during flight were noted for mean arterial pressure and oxygenation. CONCLUSION: The main finding was that there was no overall difference in mortality risk based on mission time. We conclude that transport distances or accessibility to critical care in the tertiary care center in a geographically large but sparsely populated region is not clearly associated with mortality risk.

The role of glia in protein aggregation.

Protein aggregation diseases involve intracellular accumulation or extracellular deposition of certain protein species in neuronal or glial cells, leading to neurodegeneration and shortened lifespan. Prime examples include Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), which are affected by overlapping or specific aggregation-prone proteins. Mounting evidence suggests that dysfunctional glial cells may be major drivers for some diseases, and when they are not causal factors, they could still significantly exacerbate or alleviate disease progression by playing a plethora of detrimental or beneficial roles. Here we review the diverse functions performed by glial cells in a variety of protein aggregation diseases, highlighting the complexity of the issue and the interconnected relationships between these multifaceted effects.

Astrocyte-to-astrocyte contact and a positive feedback loop of growth factor signaling regulate astrocyte maturation.

Astrocytes are critical for the development and function of the central nervous system. In developing brains, immature astrocytes undergo morphological, molecular, cellular, and functional changes as they mature. Although the mechanisms that regulate the maturation of other major cell types in the central nervous system such as neurons and oligodendrocytes have been extensively studied, little is known about the cellular and molecular mechanisms that control astrocyte maturation. Here, we identified molecular markers of astrocyte maturation and established an in vitro assay for studying the mechanisms of astrocyte maturation. Maturing astrocytes in vitro exhibit similar molecular changes and represent multiple molecular subtypes of astrocytes found in vivo. Using this system, we found that astrocyte-to-astrocyte contact strongly promotes astrocyte maturation. In addition, secreted signals from microglia, oligodendrocyte precursor cells, or endothelial cells affect a small subset of astrocyte genes but do not consistently change astrocyte maturation. To identify molecular mechanisms underlying astrocyte maturation, we treated maturing astrocytes with molecules that affect the function of tumor-associated genes. We found that a positive feedback loop of heparin-binding epidermal growth factor-like growth factor (HBEGF) and epidermal growth factor receptor (EGFR) signaling regulates astrocytes maturation. Furthermore, HBEGF, EGFR, and tumor protein 53 (TP53) affect the expression of genes important for cilium development, the circadian clock, and synapse function. These results revealed cellular and molecular mechanisms underlying astrocytes maturation with implications for the understanding of glioblastoma.

Somatic copy number mosaicism in human skin revealed by induced pluripotent stem cells.

Reprogramming somatic cells into induced pluripotent stem cells (iPSCs) has been suspected of causing de novo copy number variation. To explore this issue, here we perform a whole-genome and transcriptome analysis of 20 human iPSC lines derived from the primary skin fibroblasts of seven individuals using next-generation sequencing. We find that, on average, an iPSC line manifests two copy number variants (CNVs) not apparent in the fibroblasts from which the iPSC was derived. Using PCR and digital droplet PCR, we show that at least 50% of those CNVs are present as low-frequency somatic genomic variants in parental fibroblasts (that is, the fibroblasts from which each corresponding human iPSC line is derived), and are manifested in iPSC lines owing to their clonal origin. Hence, reprogramming does not necessarily lead to de novo CNVs in iPSCs, because most of the line-manifested CNVs reflect somatic mosaicism in the human skin. Moreover, our findings demonstrate that clonal expansion, and iPSC lines in particular, can be used as a discovery tool to reliably detect low-frequency CNVs in the tissue of origin. Overall, we estimate that approximately 30% of the fibroblast cells have somatic CNVs in their genomes, suggesting widespread somatic mosaicism in the human body. Our study paves the way to understanding the fundamental question of the extent to which cells of the human body normally acquire structural alterations in their DNA post-zygotically.