The impact of SARS-CoV-2 on respiratory syndromic and sentinel surveillance in Israel, 2020: a new perspective on established systems

Background

The COVID-19 pandemic presented new challenges for the existing respiratory surveillance systems, and adaptations were implemented. Systematic assessment of the syndromic and sentinel surveillance platforms during the pandemic is essential for understanding the value of each platform in the context of an emerging pathogen with rapid global spread.

Aim

We aimed to evaluate systematically the performance of various respiratory syndromic surveillance platforms and the sentinel surveillance system in Israel from 1 January to 31 December 2020.

Methods

We compared the 2020 syndromic surveillance trends to those of the previous 3 years, using Poisson regression adjusted for overdispersion. To assess the performance of the sentinel clinic system as compared with the national SARS-CoV-2 repository, a cubic spline with 7 knots and 95% confidence intervals were applied to the sentinel network's weekly percentage of positive SARS-CoV-2 cases.

Results

Syndromic surveillance trends changed substantially during 2020, with a statistically significant reduction in the rates of visits to physicians and emergency departments to below previous years' levels. Morbidity patterns of the syndromic surveillance platforms were inconsistent with the progress of the pandemic, while the sentinel surveillance platform was found to reflect the national circulation of SARS-CoV-2 in the population.

Conclusion

Our findings reveal the robustness of the sentinel clinics platform for the surveillance of the main respiratory viruses during the pandemic and possibly beyond. The robustness of the sentinel clinics platform during 2020 supports its use in locations with insufficient resources for widespread testing of respiratory viruses.

Lineage-matched versus mismatched influenza B vaccine effectiveness following seasons of marginal influenza B circulation

BACKGROUND

Several countries have recently transitioned from the trivalent inactivated influenza vaccine (TIV) to the quadrivalent inactivated influenza vaccine (QIV) in order to outweigh influenza B vaccine-mismatch. However, few studies thus far evaluated its benefits versus the TIV in a systematic manner. Our objective was to compare the QIV VE with lineage-mismatched TIV VE.

METHODS

We estimated the 2015-2016, 2017-2018, 2019-2020 end-of season influenza B VE against laboratory-confirmed influenza-like illness (ILI) among community patients, using the test-negative design. VE was estimated for pre-determined age groups and for moving age intervals of 15 years.

RESULTS

Since 2011-2012 season, alternate seasons in Israel were dominated by influenza B circulation. Compared with the lineage-mismatched TIV used during the 2015-2016 and 2017-2018 seasons, the 2019-2020 QIV showed the highest all-ages VE, with VE estimates of 56.9 (95% CI 30.1 to 73.4), 16.5 (95% CI -22.5 to 43.1) and -25.8 (95% CI -85.3 to 14.6) for the 2019-2020, 2017-2018 and 2015-2016 seasons, respectively. The 2019-2020 VE point estimated were the highest for the 0.5-4, 5-17 and 18-44 years age groups and for more 15-year age intervals as compared to the other seasons.

CONCLUSIONS

Our results support the rapid transition from the TIV to the QIV.

Diversity in the Circulation of Influenza A(H3N2) Viruses in the Northern Hemisphere in the 2018-19 Season

While vaccination is considered the most effective means to prevent influenza infection, its seasonal effectiveness varies, depending on the circulating influenza strains. Here, we characterized the circulation of influenza strains in October-2018 and March-2019 around the world. For this, we used nasopharyngeal samples collected from outpatient and hospitalized patients in Israel and data reported in ECDC, CDC, and WHO databases. Influenza A(H3N2) was dominant in Israel, while in Europe, Asia, and USA, A(H1N1)pdm09 virus circulated first, and then the A(H3N2) virus also appeared. Phylogenetic analysis indicated that A(H3N2) viruses circulating in Israel belonged to clade-3C.3a, while in Europe, Asia, and USA, A(H3N2) viruses belonged to subclade-3C.2a1, but were later replaced by clade-3C.3a viruses in USA. The vaccine A(H3N2) components of that year, A/Singapore/INFIMH-16-0019/2016-(H3N2)-like-viruses, belonged to clade-3C.2a1. The circulation of different influenza subtypes and clades of A(H3N2) viruses in a single season highlights the need for universal influenza vaccines.

Influenza vaccine effectiveness against laboratory-confirmed influenza in a vaccine-mismatched influenza B-dominant season

BACKGROUND

The 2017-2018 influenza season in Israel was characterized by the predominance of influenza B Yamagata, with a lesser circulation of influenza A(H1N1)pdm09 and influenza A(H3N2). We estimated vaccine effectiveness (VE) of the inactivated influenza vaccine which was selected for use that season.

METHODS

End-of-season VE and 95% confidence intervals (CI) against laboratory-confirmed influenza-like illness (ILI) were estimated by means of the test-negative design. Age-specific VE analysis was carried out using a moving age interval.

RESULTS

Specimen were obtained from 1,453 community ILI patients; 610 (42.0%) were influenza-positive, among which 69.7% were B, 17.2% A(H1N1)pdm09 and 13.4% A(H3N2). A 98.6% of molecularly characterized influenza B belonged to the Yamagata lineage. Of the sampled individuals, 1320 were suitable for VE analysis. Of those vaccinated, 90.6% received the inactivated trivalent influenza vaccine (TIV) containing a Victoria lineage influenza B-like virus. VE against influenza A differed by age, with the highest VE of 72.9% (95%CI 31.9-89.2%) observed in children 0.5-14 years old, while all ages VE was 46.6% (95%CI 10.4-68.2%). All ages VE against influenza B was 23.2% (95%CI -10.1-46.4%) with age-specific analysis showing non-significant VE estimates. Utilizing a moving age interval of 15 years, afforded a detailed age-specific insight into influenza VE against the influenza viruses circulating during the 2017-2018 season.

CONCLUSIONS

The moderate-high 2017-2018 influenza A VE among children and adolescents, supports seasonal influenza vaccination at a young age. The low VE against influenza B in Israel, is most likely the result of influenza B/TIV-mismatch.

Seropositivity of measles antibodies in the Israeli population prior to the nationwide 2018 - 2019 outbreak

Measles vaccine is administered in Israel as part of the routine childhood immunization program, at ages 1 and 6 years. In this study, we assessed seropositivity of the Israeli population against measles before the onset and propagation of the 2018-2019 measles outbreak. From the Israel Center for Disease Control National Serum Bank, 3,164 samples collected during 2015 were tested for measles antibodies. All the tests were performed using Enzyme-Linked Immunosorbent Assay (ELISA) commercial kit (Enzygnost, Anti-Measles Virus/IgG: Behring, Marburg, Germany). The overall seropositivity rate for measles was 90.7%. The seropositivity rate at 6 months and younger was 48.9%, and decreased to 3.8% among infants aged 6-11 months. Seropositivity increased to 90.7% in the 1-4-year age group, and reached 96.1% for 5-9 year-old children. Our results suggest high immunity in the Israeli population against measles virus, but not high enough to prevent outbreaks because of pockets of specific population groups with low immunization coverage. Infants between ages 6 and 11 months and children younger than 2 years had the lowest seropositivity rates being the age groups with the highest attack rates of measles during the epidemic of 2018. Efforts should be aimed at avoiding any delay in vaccination once a child reaches the age of 1 year and improving immunity levels in children aged 1-4 years.

Comprehensive Analyses of SARS-CoV-2 Transmission in a Public Health Virology Laboratory

SARS-CoV-2 has become a major global concern as of December 2019, particularly affecting healthcare workers. As person-to-person transmission is airborne, crowded closed spaces have high potential for rapid virus spread, especially early in the pandemic when social distancing and mask wearing were not mandatory. This retrospective study thoroughly investigates a small-scale SARS-CoV-2 outbreak in Israel’s central virology laboratory (ICVL) in mid-March 2020, in which six staff members and two related family members were infected. Suspicions regarding infection by contaminated surfaces in ICVL facilities were nullified by SARS-CoV-2 negative real time polymerase chain reaction (PCR) of work surfaces swipe tests. Complete SARS-CoV-2 genomes were sequenced and mutation analyses showed inclusion of all samples to clades 20B and 20C, possessing the spike mutation D614G. Phylogenetic analysis clarified transmission events, confirming S1 as having infected at least three other staff members and refuting the association of a staff member’s infected spouse with the ICVL transmission cluster. Finally, serology tests exhibited IgG and IgA antibodies in all infected individuals and revealed the occurrence of asymptomatic infections in additional staff members. This study demonstrates the advantages of molecular epidemiology in elucidating transmission events and exemplifies the importance of good laboratory practice, distancing and mask wearing in preventing SARS-CoV-2 spread, specifically in healthcare facilities.

Predominance of a Drifted Influenza A (H3N2) Clade and its Association with Age-specific Influenza Vaccine Effectiveness Variations, Influenza Season 2018-2019

Background: Influenza A (H3N2) clade 3C.3a was the predominant influenza virus in Israel throughout the 2018-2019 season, constituting a drift from the influenza A (H3N2) vaccine. We estimated the end-of season vaccine effectiveness (VE) by age, among community patients with influenza-like illness (ILI), considering the hemagglutinin (HA) gene mutations and amino acid substitutions of influenza A (H3N2) viruses detected. Methods: Nose-throat samples were analyzed for the presence of influenza virus, type/subtype, and HA gene sequence. HA gene sequences and amino acid substitutions were compared to the influenza A/Singapore/INFIMH-16-0019/2016 (H3N2)-like 2018-2019 vaccine virus, and a phylogenetic tree was generated. Influenza VE against influenza A (H3N2) was estimated using the test-negative design. VE was estimated by age group and by 15 year moving age intervals. Results: In total, 90% of the influenza A (H3N2) viruses belonged to the 3C.3a clade, constituting a unique situation in the northern hemisphere. Adjusted all-age influenza A (H3N2) VE was −3.5% (95% CI: −51.2 to 29.1). Although adjusted VEs were very low among infants, children, and young adults, a VE of 45% (95% CI: −19.2 to 74.6) was estimated among adults aged ≥45 years old. Conclusions: The higher VE point estimates among older adults may be related to previous exposure to similar influenza viruses.

Effectiveness of influenza vaccine in preventing medically-attended influenza virus infection in primary care, Israel, influenza seasons 2014/15 and 2015/16

Influenza vaccine is recommended for the entire population in Israel. We assessed influenza vaccine effectiveness (VE) for the 2014/15 and 2015/16 seasons in Israel, for the first time. Methods: Combined nose and throat swab specimens were collected from patients with influenza-like illness (ILI) presenting to sentinel primary care clinics and tested for influenza virus by RT-PCR. VE of the trivalent inactivated vaccine (TIV) was assessed using test-negative case–control design. Results: During the 2014/15 season 1,142 samples were collected; 327 (28.6%) were positive for influenza, 83.8% A(H3N2), 5.8% A(H1N1)pdm09, 9.2% B and 1.2% A un-subtyped. Adjusted VE against all influenza viruses for this influenza season was −4.8% (95% confidence interval (CI): −54.8 to 29.0) and against influenza A(H3N2), it was −15.8% (95% CI: −72.8 to 22.4). For the 2015/16 season, 1,919 samples were collected; 853 (44.4%) were positive for influenza, 43.5% A(H1N1)pdm09, 57% B, 0.7% A(H3N2) and 11 samples positive for both A(H1N1)pdm09 and B. Adjusted VE against all influenza viruses for this influenza season was 8.8% (95% CI: −25.1 to 33.5), against influenza A(H1N1)pdm09, it was 32.3% (95% CI: (−4.3 to 56.1) and against influenza B, it was −2.2% (95% CI: (−47.0 to 29.0). Conclusions: Using samples from patients with ILI visiting sentinel clinics in Israel, we demonstrated the feasibility of influenza VE estimation in Israel.

Rhinovirus infections in infants suggest that early detection can prevent unnecessary treatment

BACKGROUND

Human rhinoviruses (hRV) are small, RNA viruses of the Picornaviridae family, which are divided into three subtypes (A, B, C). hRVs are among the most common causes for acute respiratory illnesses (ARI) involving both the upper and lower respiratory tract.

OBJECTIVES

This study aimed to assess the magnitude and characteristics of hRV infections in hospitalized children, aged less than 5 years, hospitalized in Israel during 2011-2012.

STUDY DESIGN

The 2503 respiratory samples were subjected to real-time PCR, to detect hRV and other respiratory viruses. Rhinovirus-positive samples were further tested by sequencing to identify the infecting species.

RESULTS

Of these 2503 respiratory samples, 422 tested positive for hRV, of them, 243 were from children under 5 years of age (58% of all rhinoviral-positive samples). We also found that among the ARI-associated hospital admissions, 16% were positive for rhinovirus. hRV type A was the most common species. Laboratory data showed monocytosis in 51%, hypercalcemia in 61% and lower respiratory tract involvement in 75% of patients.

CONCLUSIONS

We thus recommend including rhinovirus testing as part of the routine testing performed in young children presenting with ARI.

Comparison of the new fully automated extraction platform eMAG to the MagNA PURE 96 and the well-established easyMAG for detection of common human respiratory viruses

Respiratory viral infections constitute the majority of samples tested in the clinical virology laboratory during the winter season, and are mainly diagnosed using molecular assays, namely real-time PCR (qPCR). Therefore, a high-quality extraction process is critical for successful, reliable and sensitive qPCR results. Here we aimed to evaluate the performance of the newly launched eMAG compared to the fully automated MagNA PURE 96 (Roche, Germany) and to the semi-automated easyMAG (bioMerieux, France) extraction platforms. For this analysis, we assessed and compared the analytic and clinical performance of the three platforms, using 262 archived respiratory samples positive or negative to common viruses regularly examined in our laboratory (influenza A, B, H1N1pdm, Respiratory Syncytial Virus (RSV), human Metapneumovirus (hMPV), parainfluenza-3, adenovirus and negative samples). In addition, quantitated virus controls were used to determine the limit of detection of each extraction method.

In all categories tested, eMAG results were comparable to those of the easyMAG and MagNa PURE 96, highly sensitive for all viruses and over 98% clinical specificity and sensitivity for all viruses tested. Together with its high level of automation, the bioMerieux eMAG is a high-quality extraction platform enabling effective molecular analysis and is mostly suitable for medium-sized laboratories.

Exceptional influenza morbidity in summer season of 2017 in Israel may predict the vaccine efficiency in the coming winter

Influenza infections are the leading cause of respiratory viral infections worldwide, and are mostly common in the winter season. The seasonal influenza vaccine is currently the most effective preventive modality against influenza infection. Immediately following each winter season the World Health Organization (WHO) announces the vaccine composition for the following winter. Unexpectedly, during the summer of 2017, in Israel, we observed in hospitalized patients, an exceptionally high numbers of Influenza positive cases. The majority of the influenza B infections were caused by influenza B/Yamagata lineage, which did not circulate in Israel in the previous winter, and most of the influenza A infections were caused by influenza A/H3N2, a strain similar to the strain that circulated in Israel in the previous winter. We therefore predict that these two viruses will circulate in the coming winter of 2017/18 and that the trivalent vaccine, which includes antigenically different viruses will be inefficient.

Genetic divergence of Influenza A(H3N2) amino acid substitutions mark the beginning of the 2016-2017 winter season in Israel

BACKGROUND

Influenza vaccine composition is reevaluated each year due to the frequency and accumulation of genetic changes that influenza viruses undergo. The beginning of the 2016-2017 influenza surveillance period in Israel has been marked by the dominance of influenza A(H3N2).

OBJECTIVES

To evaluate the type, subtype, genetic evolution and amino acid substitutions of influenza A(H3N2) viruses detected among community patients with influenza-like illness (ILI) and hospitalized patients with respiratory illness in the first weeks of the 2016-2017 influenza season.

STUDY DESIGN

Respiratory samples from community patients with influenza-like illness and from hospitalized patients underwent identification, subtyping and molecular characterization. Hemagglutinin sequences were compared to the vaccine strain, phylogenetic tree was created, and amino acid substitutions were determined.

RESULTS

Influenza A(H3N2) predominated during the early stages of the 2016-2017 influenza season. Noticeably, approximately 20% of community patients and 36% of hospitalized patients, positive for influenza3), received the 2016-2017 influenza vaccine. The influenza A(H3N2) viruses demonstrated genetic divergence from the vaccine strain into three separate subgroups within the 3C.2a clade. One resembled the new 3C.2a1 subclade, one resembled the recently proposed 3C.2a2 subclade and the other was not previously described. Diversity was observed within each subgroup, in terms of additional amino acid substitutions.

CONCLUSIONS

Characterization of the 2016-2017 A(H3N2) influenza viruses is imperative for determining the future influenza vaccine composition.

Ineffectiveness of the 2014-2015 H3N2 influenza vaccine

The seasonal influenza vaccine is currently the most effective preventive modality against influenza infection. Nasopharyngeal samples of vaccinated and non-vaccinated patients presenting with Influenza-like-illness (ILI) were collected from over 20 outpatient clinics located in different geographic parts of Israel and were tested for the presence of influenza viruses (influenza A and influenza B). Here we show, that in the 2014-2015 season, the vaccine that included the A/Texas/50/2012 H3N2 virus was ineffective. Significant numbers of individuals vaccinated with the 2014-2015 vaccine, of all ages, were infected with influenza A (H3N2), manifesting similar symptoms as the non-vaccinated group. We further demonstrate that the Israeli circulating influenza A(H3N2) virus was different than that included in the 2014-2015 northern hemisphere vaccine, and that antibodies elicited by this vaccine were significantly less efficient in neutralizing influenza A(H3N2) infection.

Human enterovirus D68 in clinical and sewage samples in Israel

BACKGROUND

Since mid-August 2014, North America experienced a wide outbreak of Enterovirus D68 (EV-D68) associated with severe respiratory illness in children. Several other countries also reported cases of EV-D68 in 2014.

OBJECTIVES

The aim of this study was to determine whether EV-D68 circulated in Israel in 2014, caused severe respiratory illness in children and was the causative agent of Acute Flaccid Paralysis.

STUDY DESIGN

Archived clinical respiratory samples from a cohort of 710 hospitalized pediatric patient's (<10years old) with respiratory illness were screened for clade B specific EV-D68 by real-time PCR. The patients were seen at four medical centers covering the entire country between August and November 2014. We also evaluated 49 patient stool samples from 26 AFP cases during 2014 for presence of EV-D68. In addition, RNA from sewage samples collected throughout Israel during the same study period was also tested for EV-D68. Partial VP1 sequencing was performed on all positive samples.

RESULTS

Of the 710 clinical samples evaluated, 7 (1%) were positive for EV-D68. Two patients were from the central part of Israel, while the rest was from the southern part. The majority of the patients did not have any underlying disease. Not only that, but, none of the 26 suspected AFP cases had EV-D68 nucleic acid in their stool samples. EV-D68 RNA was detected in 9 out of 93 sewage samples, mainly from Southern Israel. Sequence analysis of EV-D68 VP1 gene from both sewage and clinical samples indicated that the Israeli EV-D68 RNA belonged to Clade B which was genetically similar to 2014 circulating European and North American EV-D68 virus.

CONCLUSIONS

EV-D68 circulated in Israel during the 2014 summer-fall season and caused hospitalization of a small percent of the patients with respiratory illness.

Bone quality is affected by food restriction and by nutrition-induced catch-up growth

Growth stunting constitutes the most common effect of malnutrition. When the primary cause of malnutrition is resolved, catch-up (CU) growth usually occurs. In this study, we have explored the effect of food restriction (RES) and refeeding on bone structure and mechanical properties. Sprague-Dawley male rats aged 24 days were subjected to 10 days of 40% RES, followed by refeeding for 1 (CU) or 26 days long-term CU (LTCU). The rats fed ad libitum served as controls. The growth plates were measured, osteoclasts were identified using tartrate-resistant acid phosphatase staining, and micro-computed tomography (CT) scanning and mechanical testing were used to study structure and mechanical properties. Micro-CT analysis showed that RES led to a significant reduction in trabecular BV/TV and trabecular number (Tb.N), concomitant with an increase in trabecular separation (Tb.Sp). Trabecular BV/TV and Tb.N were significantly greater in the CU group than in the RES in both short- and long-term experiments. Mechanical testing showed that RES led to weaker and less compliant bones; interestingly, bones of the CU group were also more fragile after 1 day of CU. Longer term of refeeding enabled correction of the bone parameters; however, LTCU did not achieve full recovery. These results suggest that RES in young rats attenuated growth and reduced trabecular bone parameters. While nutrition-induced CU growth led to an immediate increase in epiphyseal growth plate height and active bone modeling, it was also associated with a transient reduction in bone quality. This should be taken into consideration when treating children undergoing CU growth.

A serum component mediates food restriction-induced growth attenuation

Proper nutrition in terms of calories and essential food components is required to maximize longitudinal growth in children. Our previous study showed that prepubertal male rats subjected to 10 days of 40% food restriction (RES) exhibited a dramatic reduction in weight and epiphyseal growth plate height, as well as changes in gene expression and microRNAs (miRNAs) in the epiphyseal growth plate. These findings reversed rapidly after renewal of the regular food supply (catch-up [CU]). To further elucidate the mechanisms underlying the nutrition-growth association, serum collected from the RES and CU rats and control rats fed ad libitum (AL) was added to the culture medium of the chondrocyte cell line ATDC5 (instead of fetal calf serum). Serum from the RES group induced a reduction in cell viability (25%, P < .05) concomitant with an increase in cell differentiation compared with that for the AL group serum. The most interesting observation, in our opinion, was the significant reduction in the expression of specific miRNAs, including the chondro-specific miR-140. These effects were not observed for serum from refed (CU) rats. Serum levels of IGF-I, leptin, and fibroblast growth factor 21 were reduced by food restriction. The addition of IGF-I and leptin to the culture increased cell viability, whereas fibroblast growth factor 21 reduced it, suggesting the involvement of IGF-I, leptin, and possibly other still unidentified serum factors in chondrocyte cell growth. In conclusion, specific miRNAs respond to nutritional cues, and these effects are mediated by serum-borne factors. These results may promote the development of superior interventions for children with malnutrition and growth abnormalities.

Nutritional catch-up growth

Malnutrition, marked by variant nutrient deficiencies, is considered a leading cause of stunted growth worldwide. In developing countries, malnutrition is caused mainly by food shortage and infectious diseases. Malnutrition may also be found in the developed world, where it is due mostly to prematurity, chronic diseases, and anorexia nervosa. In most cases, when food consumption is corrected, spontaneous catch-up (CU) growth occurs. However, CU growth is not always complete, leading to growth deficits. Therefore, it is important to understand the mechanisms that govern this process. Using a rat model of food restriction followed by refeeding, we established a nutrition-induced CU growth model. Levels of leptin and insulin-like growth factor-1 were found to significantly decrease when food was restricted and to increase already 1 day after refeeding. Gene expression analysis of the growth plate revealed that food restriction specifically affects transcription factors such as the hypoxia inducible factor-1 and its downstream targets on the one hand, and global gene expression, indicating epigenetic regulation, on the other. Food restriction also reduced the level of several microRNAs, including the chondrocyte-specific miR-140, which led to an increase in its target, SIRT1, a class III histone deacetylase. These findings may explain the global changes in gene expression observed under nutritional manipulation. We suggest that multiple levels of regulation, including transcription factors, epigenetic mechanisms, and microRNAs respond to nutritional cues and offer a possible explanation for some of the effects of food restriction on epiphyseal growth plate growth. The means whereby these components sense changes in nutritional status are still unknown. Deciphering the role of epigenetic regulation in growth may pave the way for the development of new treatments for children with growth disorders.

MicroRNAs in the growth plate are responsive to nutritional cues: association between miR-140 and SIRT1

MicroRNAs (miRNAs) have been reported to be involved in a variety of functions, including skeletal development and longitudinal growth. The aim of this study was to investigate the role of miRNAs in food-restriction-induced growth attenuation and nutrition-induced catch-up growth in the epiphyseal growth plate (EGP). Prepubertal rats were fed ad libitum or were subjected to 40% food restriction for 10 days followed by a renewal of the regular food supply. At sacrifice, tibial EGPs were excised, and the total RNA was extracted and loaded on miRNA microarrays. The miRNA microarray yielded more than 400 miRNAs that are expressed in the EGP of mature animals. Results were confirmed by quantitative polymerase chain reaction. Chondrocyte-specific miR-140-3p showed the highest expression in the mature EGP, and it was one of the few miRNAs that were significantly reduced following nutrition restriction. Changes in predicted miRNA targets were then followed with Western immunoblotting. Direct binding was demonstrated using exogenous miRNA, the 3'UTR of the target mRNA and a luciferase reporter assay. Nutrition restriction induced an increase in the level of the miR-140-3p target, NAD+-dependent SIRT1. This study is the first to show that SIRT1 and miRNAs expressed in the mature EGP are responsive to nutritional cues. Nutrition-induced epigenetic regulation of growth activates two parts of the epigenetic world - miRNAs and histone deacetylases - that are interconnected. Deciphering the role of epigenetic regulation in growth may open a new era of research and pave the way for the development of new treatments for children with growth disorders.