MAFLD in Obese Children: A Challenging Definition

Not Only Metabolic Complications of Childhood Obesity

The increasing incidence of obesity in the pediatric population requires attention to its serious complications. It turns out that in addition to typical, well-known metabolic complications, obesity as a systemic disease carries the risk of equally serious, although less obvious, non-metabolic complications, such as cardiovascular diseases, polycystic ovary syndrome, chronic kidney disease, asthma, thyroid dysfunction, immunologic and dermatologic conditions, and mental health problems. They can affect almost all systems of the young body and also leave their mark in adulthood. In addition, obesity also contributes to the exacerbation of existing childhood diseases. As a result, children suffering from obesity may have a reduced quality of life, both physically and mentally, and their life expectancy may be shortened. It also turns out that, in the case of obese pregnant girls, the complications of obesity may also affect their unborn children. Therefore, it is extremely important to take all necessary actions to prevent the growing epidemic of obesity in the pediatric population, as well as to treat existing complications of obesity and detect them at an early stage. In summary, physicians treating a child with a systemic disease such as obesity must adopt a holistic approach to treatment.

The Intersection of Genetic Factors, Aberrant Nutrient Metabolism and Oxidative Stress in the Progression of Cardiometabolic Disease

Cardiometabolic disease (CMD), which encompasses metabolic-associated fatty liver disease (MAFLD), chronic kidney disease (CKD) and cardiovascular disease (CVD), has been increasing considerably in the past 50 years. CMD is a complex disease that can be influenced by genetics and environmental factors such as diet. With the increased reliance on processed foods containing saturated fats, fructose and cholesterol, a mechanistic understanding of how these molecules cause metabolic disease is required. A major pathway by which excessive nutrients contribute to CMD is through oxidative stress. In this review, we discuss how oxidative stress can drive CMD and the role of aberrant nutrient metabolism and genetic risk factors and how they potentially interact to promote progression of MAFLD, CVD and CKD. This review will focus on genetic mutations that are known to alter nutrient metabolism. We discuss the major genetic risk factors for MAFLD, which include Patatin-like phospholipase domain-containing protein 3 (PNPLA3), Membrane Bound O-Acyltransferase Domain Containing 7 (MBOAT7) and Transmembrane 6 Superfamily Member 2 (TM6SF2). In addition, mutations that prevent nutrient uptake cause hypercholesterolemia that contributes to CVD. We also discuss the mechanisms by which MAFLD, CKD and CVD are mutually associated with one another. In addition, some of the genetic risk factors which are associated with MAFLD and CVD are also associated with CKD, while some genetic risk factors seem to dissociate one disease from the other. Through a better understanding of the causative effect of genetic mutations in CMD and how aberrant nutrient metabolism intersects with our genetics, novel therapies and precision approaches can be developed for treating CMD.

Kidney damage predictors in children with metabolically healthy and metabolically unhealthy obesity phenotype

BACKGROUND

Obesity and kidney damage have been closely linked in adults, but little is still known in childhood.

OBJECTIVE

To identify predictors of kidney damage in children with metabolically healthy (MHO) and metabolically unhealthy (MUO) obesity phenotypes.

METHODS

We retrospectively examined 396 children with obesity (mean age 10.72 ± 2.71 years, body mass index-standard deviation score, BMI-SDS, 2.23 ± 0.57) stratified according to metabolic phenotypes. Kidney damage was defined as the presence of reduced estimated glomerular filtration rate (eGFR < 90 mL/min/1.73m2) and/or albuminuria (≥ 30 mg/g urinary creatinine).

RESULTS

Kidney damage was found in 20.9% of the study population. Children with kidney damage had higher BMI-SDS, homeostasis model assessment of insulin resistance (HOMA-IR), and inflammation markers levels and increased prevalence of non-alcoholic fatty liver disease (NAFLD) than those without kidney damage (all p < 0.005). MUO and MHO subjects had respectively an odds ratio (OR) to show kidney damage of of 1.92 (95%CI:1.22-3.01; p = 0.005) and 1.05 (95%CI:1.00-1.09; p = 0.028) after adjustments. Moreover, we found that only HOMA-IR was closely associated to kidney damage in MUO group (OR = 2.07;95%CI:1.20-3.57; p = 0.007), while HOMA-IR (OR = 1.15;95%CI:1.02-1.29; p = 0.011) and uric acid (OR = 1.15;95% CI:1.02-1.30; p = 0.010) were the only significant risk factors for kidney damage in MHO group.

CONCLUSION

An increased risk of kidney damage has been observed in children with obesity and in particular in those with MUO phenotype. As their role on kidney function, HOMA-IR should be monitored in MUO children and both HOMA-IR and uric acid in MHO children.

The challenging role of micro-RNAs in non-alcoholic fatty liver disease in children with obesity: is it time for a new era?

INTRODUCTION

As the pediatric obesity epidemic, nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease in childhood. Pediatric NAFLD pathophysiology is tangled and still unclear, but insulin resistance (IR), genetics, epigenetics, oxidative stress, and inflammation act as key players. Due to the increased cardiometabolic risk of these patients, several biomarkers have been proposed for early NAFLD identification, but their clinical utility is poor. Recently, hepatic dysregulation of microRNAs (miRNAs) has been linked to metabolic dysfunction, which in turn implied in NAFLD development. Evidence on the intriguing role of miRNAs in NAFLD pathogenesis has emerging especially in at-risk children such as those with obesity. However, pediatric evidence supporting their potential use as early noninvasive NAFLD tools is still limited but promising.

AREAS COVERED

We provided an overview on the emerging role of miRNAs in pediatric NAFLD by addressing some issues regarding their pathophysiological link with the metabolic milieu and their role as reliable NAFLD markers in children with obesity.

EXPERT OPINION

Strong evidence supports a potential role of miRNAs as early biomarkers of NAFLD in children with obesity. They might represent a valid diagnostic and targeted therapeutic tool due to its close pathogenic link with the metabolic milieu.

Is Metabolic Syndrome Useful for Identifying Youths with Obesity at Risk for NAFLD?

The definition of metabolic syndrome (MetS) in childhood is controversial. Recently, a modified version of the International Diabetes Federation (IDF) definition was proposed using reference data from an international population for high waist circumference (WC) and blood pressure (BP), while the fixed cutoffs for lipids and glucose were not changed. We analyzed MetS prevalence using this modified definition (MetS-IDF_m) and its association with non-alcoholic fatty liver disease (NAFLD) in 1057 youths (age 6-17 years) with overweight/obesity (OW/OB). A comparison with another modified definition of MetS according to the Adult Treatment Panel III (MetS-ATPIII_m) was performed. The prevalence of MetS-IDF_m was 27.8% and 28.9% by MetS-ATPIII_m. The Odds (95% Confidence Intervals) of NAFLD was 2.70 (1.30-5.60) (p = 0.008) for high WC, 1.68 (1.25-2.26)(p = 0.001) for MetS, 1.54 (1.12-2.11)(p = 0.007) for low HDL-Cholesterol, 1.49 (1.04-2.13)(p = 0.032) for high triglycerides and 1.37 (1.03-1.82)(p = 0.033) for high BP. No substantial difference was found in the prevalence of MetS-IDF_m and frequency of NAFLD compared to Mets-ATPIII_m definition. Our data demonstrate that one third of youths with OW/OB have MetS, whichever was the criterion. Neither definition was superior to some of their components in identifying youths with OW/OB at risk for NAFLD.

Uric acid versus metabolic syndrome as markers of fatty liver disease in young people with overweight/obesity

AIMS

To compare the association of high serum uric acid (HUA) or metabolic syndrome (MetS) with fatty liver disease (FLD) in youths with overweight/obesity (OW/OB).

MATERIALS AND METHODS

Cross-sectional study of anthropometrics, biochemical variables, and liver ultrasound of 3104 individuals with OW/OB (age 5-17 years). Metabolic syndrome was defined by ≥ 3 criteria among (1) high waist circumference; (2) high triglycerides; (3) low high-density lipoproteins; (4) fasting glucose ≥100 mg/dl; (5) blood pressure ≥95^th percentile in children, and ≥130/80 mmHg in adolescents. High serum uric acid was defined as serum UA value ≥ 75^th percentile adjusted for sex. Fatty liver disease was determined by echography.

RESULTS

The sample was stratified in four categories: (1) no HUA, no MetS (reference category); (2) MetS; (3) HUA; (4) HUA and MetS (HUA + MetS). The prevalence of FLD increased across the four categories from 29.9%, 44.0%, 52.2%, to 67.1%, respectively (p < 0.0001). The ORs for the categorical variables were 1.33 (1.06-1.68) for MetS (p = 0.02), 3.19 (2.51-4.05) for HUA (p < 0.0001) and 3.72 (2.65-5.21) for HUA + MetS (p < 0.0001), versus the reference category regardless of the body mass index.

CONCLUSIONS

HUA represents a useful marker of FLD in youths with OW/OB, given its greater ability to identify those at increased risk of the disease compared to MetS. The ability of both to predict incident FLD must be investigated in longitudinal study.

Metabolic-associated fatty liver disease from childhood to adulthood: State of art and future directions

In 2020, an international group of experts proposed to replace the term of nonalcoholic fatty liver disease with metabolic-associated fatty liver disease (MAFLD). This recent proposal reflects the close association of fatty liver with metabolic derangements, as demonstrated by previous robust data. Several factors [including genetics, inflammation, metabolic abnormalities, insulin resistance (IR), obesity, prenatal determinants, and gut–liver axis] have been found to be involved in MAFLD pathophysiology, but this tangled puzzle remains to be clearly understood. In particular, IR has been recognized as a key player in metabolic impairments development in children with fatty liver. On this ground, MAFLD definition focuses on the pathophysiological basis of the disease, by emphasizing the crucial role of metabolic impairments in this condition. Although primarily developed for adults, MAFLD diagnostic criteria have been recently updated with an age-appropriate definition for sex and age percentiles, because of the increasing attention to cardiometabolic risk in childhood. To date, accumulating evidence is available on the feasibility of MAFLD definition in clinical practice, but some data are still conflicting in highly selected populations. Considering the growing prevalence worldwide of fatty liver and its close relationship with metabolic dysfunction both in children and adults with subsequent increased cardiovascular risk, early strategies for MAFLD identification, treatment and prevention are needed. Novel therapeutic insights for MAFLD based on promising innovative biological techniques are also emerging. We aimed to summarize the most recent evidence in this intriguing research area both in children and adults.

Advances in pediatric non-alcoholic fatty liver disease: From genetics to lipidomics

As a result of the obesity epidemic, non-alcoholic fatty liver disease (NAFLD) represents a global medical concern in childhood with a closely related increased cardiometabolic risk. Knowledge on NAFLD pathophysiology has been largely expanded over the last decades. Besides the well-known key NAFLD genes (including the I148M variant of the PNPLA3 gene, the E167K allele of the TM6SF2, the GCKR gene, the MBOAT7-TMC4 rs641738 variant, and the rs72613567:TA variant in the HSD17B13 gene), an intriguing pathogenic role has also been demonstrated for the gut microbiota. More interestingly, evidence has added new factors involved in the “multiple hits” theory. In particular, omics determinants have been highlighted as potential innovative markers for NAFLD diagnosis and treatment. In fact, different branches of omics including metabolomics, lipidomics (in particular sphingolipids and ceramides), transcriptomics (including micro RNAs), epigenomics (such as DNA methylation), proteomics, and glycomics represent the most attractive pathogenic elements in NAFLD development, by providing insightful perspectives in this field. In this perspective, we aimed to provide a comprehensive overview of NAFLD pathophysiology in children, from the oldest pathogenic elements (including genetics) to the newest intriguing perspectives (such as omics branches).

Metabolic dysfunction is associated with steatosis but no other histologic features in nonalcoholic fatty liver disease

BACKGROUND

Recently, nonalcoholic fatty liver disease (NAFLD) has been renamed metabolic-associated fatty liver disease (MAFLD). Based on the definition for MAFLD, a group of non-obese and metabolically healthy individuals with fatty liver are excluded from the newly proposed nomenclature.

AIM

To analyze the histologic features in the MAFLD and non-MAFLD subgroups of NAFLD.

METHODS

Eighty-three patients with biopsy-proven NAFLD were separated into MAFLD and non-MAFLD groups. The diagnosis of MAFLD was established as hepatic steatosis along with obesity/diabetes or evidence of metabolic dysfunction. The histologic features were compared according to different metabolic disorders and liver enzyme levels.

RESULTS

MAFLD individuals had a higher NAFLD activity score (P = 0.002) and higher severity of hepatic steatosis (42.6% Grade 1, 42.6% Grade 2, and 14.8% Grade 3 in MAFLD; 81.8% Grade 1, 13.6% Grade 2, and 4.5% Grade 3 in non-MAFLD; P = 0.007) than the non-MAFLD group. Lobular and portal inflammation, hepatic ballooning, fibrosis grade, and the presence of nonalcoholic steatohepatitis (NASH) and significant fibrosis were comparable between the two groups. The higher the liver enzyme levels, the more severe the grades of hepatic steatosis (75.0% Grade 1 and 25.0% Grade 2 in normal liver function; 56.6% Grade 1, 39.6% Grade 2, and 3.8% Grade 3 in increased liver enzyme levels; 27.8% Grade 1, 27.8% Grade 2, and 44.4% Grade 3 in liver injury; P < 0.001). Patients with liver injury (alanine aminotransferase > 3 × upper limit of normal) presented a higher severity of hepatocellular ballooning (P = 0.021). Moreover, the grade of steatosis correlated significantly with hepatocellular ballooning degree (r = 0.338, P = 0.002) and the presence of NASH (r = 0.466, P < 0.001).

CONCLUSION

Metabolic dysfunction is associated with hepatic steatosis but no other histologic features in NAFLD. Further research is needed to assess the dynamic histologic characteristics in NAFLD based on the presence or absence of metabolic disorders.

Stratification by Non-invasive Biomarkers of Non-alcoholic Fatty Liver Disease in Children

BACKGROUND

The spectrum of non-alcoholic fatty liver disease (NAFLD) ranges from isolated hepatic steatosis to non-alcoholic steatohepatitis to fibrosis. We aimed to introduce useful biomarkers released during liver inflammation and fibrogenesis that are easy to use in outpatient clinic and adjust to children to evaluate each NAFLD stage without biopsy.

METHODS

This prospective study included 60 patients aged under 19 years whose alanine aminotransferase (ALT) levels were elevated from March 2021. All patients were proven to have NAFLD by ultrasonography and laboratory work-up to exclude other causes of hepatitis. Fibroscan and additional laboratory tests for biomarkers [procollagen type1 amino-terminal propeptide (P1NP), osteocalcin, interleukin-6 (IL-6), and Mac-2 binding protein glycosylated isomer (M2BPGi)] were performed. Fibroscan-AST (FAST) score was used for the comparison of steatohepatitis and liver stiffness measurement (kPa) was used for the comparison of advanced fibrosis.

RESULTS

The biomarker that showed a significant difference between the FAST-positive and negative groups was the P1NP/osteocalcin ratio with a p-value of 0.008. The area under receiver operating characteristic (AUROC) of P1NP/osteocalcin ratio^*ALT values (values obtained through multivariate analysis) was 0.939 with the cut-off value of 305.38. The biomarkers that showed a significant difference between the LSM-positive and negative groups were IL-6 and M2BPGi with a p-values of 0.005 and <0.001. AUROC of IL-6 ^*AST values (values obtained through multivariate analysis) was 0.821 with the cut-off value of 228.15. M2BPGi showed a significant linear relationship with LSM in Pearson correlation analysis (Pearson correlation coefficient = 0.382; p = 0.003). The diagnostic capability of M2BPGi to evaluate advanced fibrosis showed an acceptable result (AUROC = 0.742; p = 0.022).

CONCLUSIONS

Non-invasive biomarkers can be used to predict each stage of NAFLD in children. The measurements of P1NP, IL-6 or M2BPGi along with the basic chemistry tests would help determine the stage of NAFLD they correspond to at the time of initial diagnosis and predict responsiveness after the treatment.

Triglyceride to high-density lipoprotein cholesterol ratio is an independent predictor of liver fibrosis among pediatrics non-alcoholic fatty liver disease

BACKGROUND

Insulin resistance (IR), one of the key components of the metabolic syndrome, is recognized as the pathophysiological hallmark of non-alcoholic fatty liver disease (NAFLD). This study aims to investigate the relationship between surrogate markers of IR and the severity of NAFLD among overweight or obese children.

METHODOLOGY

A total of 56 consecutive children aged 6 to 18 years old were recruited from the pediatric obesity and type 2 diabetes mellitus (T2DM) clinic in University Malaya Medical Centre (UMMC) from 2016 to 2019. Data on anthropometric measurements, clinical components of metabolic syndrome and fasting serum insulin were collected. Triglyceride to high-density lipoprotein cholesterol ratio (TG: HDL-C), Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and Single Point Insulin Sensitivity Estimator (SPISE) were calculated. Transient elastography was performed with hepatic steatosis and liver fibrosis assessed by controlled attenuation parameter (CAP) and liver stiffness measurement (LSM), respectively.

RESULTS

A total of 44 children (78.6%) had liver steatosis and 35.7% had presence of significant liver fibrosis (stage F≥2). Majority (89.3%) are obese and 24 children (42.9%) were diagnosed with metabolic syndrome. Higher number of children with T2DM and significant liver fibrosis were associated with higher tertiles of TG: HDL-C ratio (p<0.05). Top tertile of TG: HDL-C ratio was an independent predictor of liver fibrosis (OR=8.14, 95%CI: 1.24-53.36, p=0.029). ROC analysis showed that the area under the curve (AUC) of HOMA-IR (0.77) and TG: HDL-C ratio (0.71) were greater than that of metabolic syndrome (0.70), T2DM (0.62) and SPISE (0.22). The optimal cut-off values of HOMA-IR and TG: HDL-C ratio for detecting liver fibrosis among children with NAFLD are 5.20 and 1.58, respectively.

CONCLUSION

Children with NAFLD and higher TG: HDL-C ratio are more likely to have liver fibrosis. TG: HDL-C ratio is a promising tool to risk stratify those with NAFLD who are at risk of developing advanced liver disease.

Metabolic Fatty Liver Disease in Children: A Growing Public Health Problem

Metabolic-associated fatty liver disease (MAFLD), previously called nonalcoholic fatty liver diseases (NAFLD), is one of the most important causes of chronic liver disease worldwide and will likely become the leading cause of end-stage liver disease in the decades ahead. MAFLD covers a continuum of liver diseases from fatty liver to nonalcoholic steatohepatitis (NASH), liver fibrosis/cirrhosis and hepatocellular cancer. Importantly, the growing incidence of overweight and obesity in childhood, 4% in 1975 to 18% in 2016, with persisting obesity complications into adulthood, is likely to be harmful by increasing the incidence of severe MAFLD at an earlier age. Currently, MAFLD is the leading form of chronic liver disease in children and adolescents, with a global prevalence of 3 to 10%, pointing out that early diagnosis is therefore crucial. In this review, we highlight the current knowledge concerning the epidemiology, risk factors and potential pathogenic mechanisms, as well as diagnostic and therapeutic approaches, of pediatric MAFLD.

Association between Hepatic Steatosis and Obstructive Sleep Apnea in Children and Adolescents with Obesity

BACKGROUND

Owing to the increasing rate of pediatric obesity, its complications such as non-alcoholic fatty liver disease (NAFLD) and obstructive sleep apnea (OSA) have become prevalent already in childhood. We aimed to assess the relationship between these two diseases in a cohort of children with obesity.

METHODS

We enrolled 153 children with obesity (mean age 10.5 ± 2.66, mean BMI 30.9 ± 5.1) showing OSA. Subjects underwent a laboratory evaluation, a cardio-respiratory polysomnography (PSG), and a liver ultrasound.

RESULTS

All subjects had a clinical diagnosis of OSA based on the AHI > 1/h (mean AHI 8.0 ± 5.9; range 2.21-19.0). Of these, 69 showed hepatic steatosis (62.3% as mild, 20.3% as moderate, and 17.4% as severe degree). A strong association between ALT and apnea/hypopnea index (AHI) was observed (p = 0.0003). This association was not confirmed after adjusting for hepatic steatosis (p = 0.53). By subdividing our population according to the presence/absence of steatosis, this association was found only in the steatosis group (p = 0.009). As the severity of steatosis increased, the significance of its association with AHI compared to the absence of steatosis became progressively stronger (all p < 0.0001).

CONCLUSIONS

Hepatic steatosis seems to drive the association between OSA and ALT levels, suggesting a potential pathogenic role of OSA in NAFLD.

Multifactorial Basis and Therapeutic Strategies in Metabolism-Related Diseases

Throughout the 20th and 21st centuries, the incidence of non-communicable diseases (NCDs), also known as chronic diseases, has been increasing worldwide. Changes in dietary and physical activity patterns, along with genetic conditions, are the main factors that modulate the metabolism of individuals, leading to the development of NCDs. Obesity, diabetes, metabolic associated fatty liver disease (MAFLD), and cardiovascular diseases (CVDs) are classified in this group of chronic diseases. Therefore, understanding the underlying molecular mechanisms of these diseases leads us to develop more accurate and effective treatments to reduce or mitigate their prevalence in the population. Given the global relevance of NCDs and ongoing research progress, this article reviews the current understanding about NCDs and their related risk factors, with a focus on obesity, diabetes, MAFLD, and CVDs, summarizing the knowledge about their pathophysiology and highlighting the currently available and emerging therapeutic strategies, especially pharmacological interventions. All of these diseases play an important role in the contamination by the SARS-CoV-2 virus, as well as in the progression and severity of the symptoms of the coronavirus disease 2019 (COVID-19). Therefore, we briefly explore the relationship between NCDs and COVID-19.

Pediatric vs. adult NAFLD to MAFLD transition: a welcome but tangled path

The term non-alcoholic fatty liver disease (NAFLD) appears unfitting both in adults and in children. As obesity and metabolic syndrome play a relevant pathogenic role, an international group of adults’ liver disease experts has proposed to rename this condition metabolic (dysfunction)-associated fatty liver disease (MAFLD). While this new more appropriate and useful definition has mostly been met with good reactions in adults, it may present a tangled path in pediatrics. Here we further stress the recommendations of the North American and the European Societies for Pediatric Gastroenterology, Hepatology and Nutrition that a hyperechogenic liver in a child affected by obesity or overweight with chronically elevated liver enzymes should not be assumed to have NAFLD only. Especially in those patients who are not in the classic age range or who have particularly severe laboratory anomalies, other genetic, metabolic (inborn errors of metabolism, IEM), endocrine, intestinal and hepatic pediatric-onset conditions, should in fact be excluded, particularly when response to a weight loss trial is not available. The term pediatric fatty liver disease (PeFLD) with three subtypes (1. contextual diagnosis of an IEM; 2. Metabolic (dysfunction)-associated fatty liver; 3. unknown cause of fatty liver) has recently been proposed aiming to separate true MAFLD from IEM and/or the other above mentioned conditions, which may be rare when considered individually but represent a large group when considered collectively. Although the cost-effectiveness ratio of this attitude is still indeterminate, it is likely that the advantage of the early identification of a specifically treatable pediatric-onset liver disease associated to/mimicking MAFLD would be rewarding.