Implication of transcription factor FOXD2 dysfunction in syndromic congenital anomalies of the kidney and urinary tract (CAKUT).

Congenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause for chronic kidney disease below age 30 years. Many monogenic forms have been discovered due to comprehensive genetic testing like exome sequencing. However, disease-causing variants in known disease-associated genes only explain a proportion of cases. Here, we aim to unravel underlying molecular mechanisms of syndromic CAKUT in three unrelated multiplex families with presumed autosomal recessive inheritance. Exome sequencing in the index individuals revealed three different rare homozygous variants in FOXD2, encoding a transcription factor not previously implicated in CAKUT in humans: a frameshift in the Arabic and a missense variant each in the Turkish and the Israeli family with segregation patterns consistent with autosomal recessive inheritance. CRISPR/Cas9-derived Foxd2 knockout mice presented with a bilateral dilated kidney pelvis accompanied by atrophy of the kidney papilla and mandibular, ophthalmologic, and behavioral anomalies, recapitulating the human phenotype. In a complementary approach to study pathomechanisms of FOXD2-dysfunction-mediated developmental kidney defects, we generated CRISPR/Cas9-mediated knockout of Foxd2 in ureteric bud-induced mouse metanephric mesenchyme cells. Transcriptomic analyses revealed enrichment of numerous differentially expressed genes important for kidney/urogenital development, including Pax2 and Wnt4 as well as gene expression changes indicating a shift toward a stromal cell identity. Histology of Foxd2 knockout mouse kidneys confirmed increased fibrosis. Further, genome-wide association studies suggest that FOXD2 could play a role for maintenance of podocyte integrity during adulthood. Thus, our studies help in genetic diagnostics of monogenic CAKUT and in understanding of monogenic and multifactorial kidney diseases.

DNAJC21-related thrombocytopenia in a young adult female.

Bone marrow failure type 3 (BMFS3) (MIM:617052) is a subtype of inherited bone marrow failure syndromes (IBMFS) caused by homozygous pathogenic variants in DNAJC21. It was first defined in 2016, and to date, 19 patients have been reported. Here we report the first adult patient; a 20-year-old female with a novel frameshift variant in DNAJC21 presents with thrombocytopenia, dysmorphic findings, and ovarian agenesis. Our patient expands the clinical spectrum to the milder end and suggests that DNAJC21-related disorders can have relatively mild presentations. Investigation of DNAJC21 variants in both childhood and adult patients with persistent, non-progressive thrombocytopenia will allow to broaden the gene-related phenotypic and genotypic spectrum and elucidate the pathophysiology. Therefore, we encourage revisiting undiagnosed patients to offer whole exome sequencing (WES) in adulthood.

Clinical features of generalized lipodystrophy in Turkey: A cohort analysis.

AIM: To describe the Turkish generalized lipodystrophy (GL) cohort with the frequency of each complication and the death rate during the period of the follow-up. METHODS: This study reports on 72 patients with GL (47 families) registered at different centres in Turkey that cover all regions of the country. The mean ± SD follow-up was 86 ± 78 months. RESULTS: The Kaplan-Meier estimate of the median time to diagnosis of diabetes and/or prediabetes was 16 years. Hyperglycaemia was not controlled in 37 of 45 patients (82.2%) with diabetes. Hypertriglyceridaemia developed in 65 patients (90.3%). The Kaplan-Meier estimate of the median time to diagnosis of hypertriglyceridaemia was 14 years. Hypertriglyceridaemia was severe (≥ 500 mg/dl) in 38 patients (52.8%). Seven (9.7%) patients suffered from pancreatitis. The Kaplan-Meier estimate of the median time to diagnosis of hepatic steatosis was 15 years. Liver disease progressed to cirrhosis in nine patients (12.5%). Liver disease was more severe in congenital lipodystrophy type 2 (CGL2). Proteinuric chronic kidney disease (CKD) developed in 32 patients (44.4%) and cardiac disease in 23 patients (31.9%). Kaplan-Meier estimates of the median time to diagnosis of CKD and cardiac disease were 25 and 45 years, respectively. Females appeared to have a more severe metabolic disease, with an earlier onset of metabolic abnormalities. Ten patients died during the follow-up period. Causes of death were end-stage renal disease, sepsis (because of recurrent intestinal perforations, coronavirus disease, diabetic foot infection and following coronary artery bypass graft surgery), myocardial infarction, heart failure because of dilated cardiomyopathy, stroke, liver complications and angiosarcoma. CONCLUSIONS: Standard treatment approaches have only a limited impact and do not prevent the development of severe metabolic abnormalities and early onset of organ complications in GL.

Mutational spectrum of congenital long QT syndrome in Turkey; identification of 12 novel mutations across KCNQ1, KCNH2, SCN5A, KCNJ2, CACNA1C, and CALM1.

INTRODUCTION: Long QT syndrome (LQTS) is of great importance as it is the most common cause of sudden cardiac death in childhood. The diagnosis is made by the prolongation of the QTc interval on the electrocardiography. However, clinical heterogeneity and nondiagnostic QTc intervals may cause a delay in the diagnosis. In such cases, genetic tests such as next-generation sequencing (NGS) panel analysis enable a definitive diagnosis. We present the first study that aimed to expand the LQTS's mutational spectrum by NGS panel analysis from Turkey. METHODS: Fifty-seven unrelated patients with clinically diagnosed LQTS were investigated using an NGS panel that includes six LQTS-related genes. Clinical aspects, outcome, and molecular analysis results were reviewed. RESULTS: Pathogenic (53%)/likely pathogenic (23%)/variant of unknown significance (4%) variants were detected in any of the genes examined in 79% of the patients. Among all detected variants, KCNQ1(71%) was the most common gene, followed by SCN5A (11%), KCNH2 (10%), CALM1 (5%), and CACNA1C (3%). Twelve novel variants were detected. Among the variants in KCNQ1, the c.1097G>A variant was present in 42% of patients. This variant also composed 31% of the variants detected in all of the genes. CONCLUSION: Our study expands the spectrum of the variations associated with LQTS with twelve novel variants in five genes. And also it draws attention to the frequency of the KCNQ1 c.1097G>A variant and forms the basis for new studies to determine the possible founder effect in the Turkish population. Furthermore, identifying new variants and clinical findings has importance in elaborating the roles of related genes in pathophysiology and determining the variable expression and incomplete penetration rates in this syndrome.

H syndrome with a novel homozygous SLC29A3 mutation in two sisters.

H syndrome (OMIM 602782) is a recently defined autosomal recessive genodermatosis. Cutaneous findings of H syndrome include hyperpigmentation, hypertrichosis, and induration, while hearing loss, heart anomalies, hepatomegaly, hypogonadism, hyperglycemia (diabetes mellitus), low height (short stature), hallux valgus (flexion contractures), and hematological abnormalities are the extracutaneous abnormalities. We report a novel homozygous missense mutation, c.416T > C p.(Leu139Pro), in the SLC29A3 (NM_001174098.1) gene in two sisters with H syndrome presenting with different phenotypes.

ADA2 deficiency in a patient with Noonan syndrome-like disorder with loose anagen hair: The co-occurrence of two rare syndromes.

Noonan syndrome-like disorder with loose anagen hair (NS/LAH) is one of the RASopathies, a group of clinically related developmental disorders caused by germline mutations in genes that encode components acting in the RAS/MAPK pathway. Among RASopathies, NS/LAH (OMIM 607721) is an extremely rare, multiple anomaly syndrome characterized by dysmorphic facial features similar to those observed in Noonan syndrome along with some distinctive ectodermal findings including easily pluckable, sparse, thin, and slow-growing hair. ADA2 deficiency (DADA2, OMIM 615688) is a monogenic autoinflammatory disorder caused by homozygous or compound heterozygous mutations in ADA2, with clinical features including recurrent fever, livedo racemosa, hepatosplenomegaly, and strokes as well as immune dysregulation. This is the first report of NS/LAH and ADA2 deficiency in the same individual. We report on a patient presenting with facial features, recurrent infections and ectodermal findings in whom both the clinical and molecular diagnoses of NS/LAH and ADA2 deficiency were established, respectively.

Further expansion of the mutational spectrum of spondylo-meta-epiphyseal dysplasia with abnormal calcification.

Spondylo-meta-epiphyseal dysplasia, short limb-abnormal calcification type, is a rare autosomal recessive disorder of the skeleton characterized by disproportionate short stature with narrow chest and dysmorphic facial features. The skeletal manifestations include platyspondyly, short flared ribs, short tubular bones with abnormal metaphyses and epiphyses, severe brachydactyly, and premature stippled calcifications in the cartilage. The abnormal calcifications are so distinctive as to point to the definitive diagnosis. However, they may be too subtle to attract diagnostic attention in infancy. Homozygous variants in DDR2 cause this disorder. We report on a 5-year-old girl with the classic phenotype of SMED, SL-AC in whom a novel homozygous nonsense mutation in DDR2 was detected using exome sequencing.

Further delineation of spondyloepimetaphyseal dysplasia Faden-Alkuraya type: A RSPRY1-associated spondylo-epi-metaphyseal dysplasia with cono-brachydactyly and craniosynostosis.

Our understanding of the molecular basis of the genetic disorders of the skeleton has steadily increased, as the application of high-throughput sequencing technology has expanded. One of the newcomers is Spondyloepimetaphyseal dysplasia Faden-Alkuraya type. In this study, we aimed to further delineate the clinical, radiographic, and molecular findings of this entity in five affected individuals from two unrelated families. All patients have short stature, extremity deformities, facial dysmorphism and intellectual disability. The skeletal hallmarks include (a) mild spondylar dysplasia, (b) epimetaphyseal dysplasia of the long bones associated with coxa vara and genu valgum, (c) brachymesophalangy with cone-shaped epiphyses, and (d) craniosynostosis. Unlike the previously reported clinical findings, all patients except one are normocephalic, and all share the clinical findings including craniosynostosis, varying degrees of intellectual disability, facial dysmorphism, and skeletal findings including pes planus, prominent heels, and pectus deformity. Interestingly one of the patients presented with a cemento-ossifying fibrous lesion of the maxilla. Whole exome sequencing revealed a novel homozygous [c.377delT] [p.Ile126fs*] frameshift mutation at exon 2 in one family, while Sanger sequencing revealed a novel homozygous splice site mutation [c.516+2T>A] at exon 4/intron 4 border of RSPRY1 in the other family. In conclusion; we provide further evidence that Spondyloepimetaphyseal dysplasia Faden-Alkuraya type is a RSPRY1-associated skeletal dysplasia with a distinctive phenotype composed of spondyloepimetaphyseal dysplasia, cono-brachydactyly, and craniosynostosis along with recognizable facial features and intellectual disability.

Prenatal and Postnatal Follow-up in Trisomies 13 and 18: A 20-Year Experience in a Tertiary Center.

OBJECTIVE: Trisomies 13 and 18 are among the most common autosomal aneuploidies associated with high mortality rates. Conventional management strategies offer to limit interventional support; however, some of the recent studies suggest that intervention does make a difference in terms of survival. STUDY DESIGN: A retrospective cohort study was performed between January 1996 and January 2016, covering all cases with such trisomies. A total of 69 cases were reviewed for clinical aspects, outcome, and management strategies. RESULTS: In almost all pregnancies with follow-up, at least one indication present for invasive testing (54/55). Invasive testing was not performed in 18.5% of such cases. All parents opted for termination in cases with prenatal diagnosis. None of the liveborns had prenatal diagnoses, thus, neonatal resuscitation and intensive care unit admission were not withheld in such infants. Major intervention was done in only one patient with full trisomy 13. Median survival for infants with full trisomies 13 and 18 was 36 and 60 days, respectively. Almost half the patients died within 1 month. CONCLUSION: To which extent the major interventions should be withheld is an issue of debate in managing such infants; however, current approaches are subject to change, given the technological advances.

Schwartz-Jampel Syndrome Type-1: Compound Heterozygosity of Two Novel Variants.

Schwartz-Jampel Syndrome (SJS) type-1 (OMIM; #255800), a rare cause of skeletal dysplasia, is characterized by myotonic myopathy, chondrodystrophy, short stature, facial and eye abnormalities. SJS Type-1 develops due to variations in the HSPG2 gene which produces the "perlecan" molecule, one of the main proteoglycans of the basement membrane. A 6-year-old girl presented with short stature, a mask face, shrunken lips, narrow palpebral opening due to blepharospasm, stiffness of facial muscles, micrognathia, overlapping teeth, a short neck, and a bell-shaped thorax due to myotonic myopathy. She was diagnosed with SJS type-1 due to compound heterozygosity of two novel variations in the HSPG2 gene. In patients with short stature and an accompanying myotonic myopathy SJS should be considered. Compound heterozygosity may cause typical clinical findings of SJS. In case of suspicion creatinine kinase levels can be measured, and the determination of myotonia may require evaluation with electromyography. Once the diagnosis is made, patients should be carefully monitored in terms of growth, neuromuscular disorders, joints problems and bone health.

Impact of deep phenotyping: high diagnostic yield in a diverse pediatric population of 172 patients through clinical whole-genome sequencing at a single center.

Background: Pediatric patients with undiagnosed conditions, particularly those suspected of having Mendelian genetic disorders, pose a significant challenge in healthcare. This study investigates the diagnostic yield of whole-genome sequencing (WGS) in a pediatric cohort with diverse phenotypes, particularly focusing on the role of clinical expertise in interpreting WGS results. Methods: A retrospective cohort study was conducted at Acibadem University's Maslak Hospital in Istanbul, Turkey, involving pediatric patients (0-18 years) who underwent diagnostic WGS testing. Clinical assessments, family histories, and previous laboratory and imaging studies were analyzed. Variants were classified and interpreted in conjunction with clinical findings. Results: The cohort comprised 172 pediatric patients, aged 0-5 years (62.8%). International patients (28.5%) were from 20 different countries. WGS was used as a first-tier approach in 61.6% of patients. The diagnostic yield of WGS reached 61.0%, enhanced by reclassification of variants of uncertain significance (VUS) through reverse phenotyping by an experienced clinical geneticist. Consanguinity was 18.6% of the overall cohort. Dual diagnoses were carried out for 8.5% of solved patients. Discussion: Our study particularly advocates for the selection of WGS as a first-tier testing approach in infants and children with rare diseases, who were under 5 years of age, thereby potentially shortening the duration of the diagnostic odyssey. The results also emphasize the critical role of a single clinical geneticist's expertise in deep phenotyping and reverse phenotyping, which contributed significantly to the high diagnostic yield.

Magnetic resonance imaging based kidney volume assessment for risk stratification in pediatric autosomal dominant polycystic kidney disease.

Introduction: In the pediatric context, most children with autosomal dominant polycystic kidney disease (ADPKD) maintain a normal glomerular filtration rate (GFR) despite underlying structural kidney damage, highlighting the critical need for early intervention and predictive markers. Due to the inverse relationship between kidney volume and kidney function, risk assessments have been presented on the basis of kidney volume. The aim of this study was to use magnetic resonance imaging (MRI)-based kidney volume assessment for risk stratification in pediatric ADPKD and to investigate clinical and genetic differences among risk groups. Methods: This multicenter, cross-sectional, and case-control study included 75 genetically confirmed pediatric ADPKD patients (5-18 years) and 27 controls. Kidney function was assessed by eGFR calculated from serum creatinine and cystatin C using the CKiD-U25 equation. Blood pressure was assessed by both office and 24-hour ambulatory measurements. Kidney volume was calculated from MRI using the stereological method. Total kidney volume was adjusted for the height (htTKV). Patients were stratified from A to E classes according to the Leuven Imaging Classification (LIC) using MRI-derived htTKV. Results: Median (Q1-Q3) age of the patients was 6.0 (2.0-10.0) years, 56% were male. There were no differences in sex, age, height-SDS, or GFR between the patient and control groups. Of the patients, 89% had PKD1 and 11% had PKD2 mutations. Non-missense mutations were 73% in PKD1 and 75% in PKD2. Twenty patients (27%) had hypertension based on ABPM. Median htTKV of the patients was significantly higher than controls (141 vs. 117 ml/m, p = 0.0003). LIC stratification revealed Classes A (38.7%), B (28%), C (24%), and D + E (9.3%). All children in class D + E and 94% in class C had PKD1 variants. Class D + E patients had significantly higher blood pressure values and hypertension compared to other classes (p > 0.05 for all). Discussion: This study distinguishes itself by using MRI-based measurements of kidney volume to stratify pediatric ADPKD patients into specific risk groups. It is important to note that PKD1 mutation and elevated blood pressure were higher in the high-risk groups stratified by age and kidney volume. Our results need to be confirmed in further studies.

Rapid genome sequencing for critically ill infants: an inaugural pilot study from Turkey.

Introduction: Rare and ultra-rare genetic conditions significantly contribute to infant morbidity and mortality, often presenting with atypical features and genetic heterogeneity that complicate management. Rapid genome sequencing (RGS) offers a timely and cost-effective approach to diagnosis, aiding in early clinical management and reducing unnecessary interventions. This pilot study represents the inaugural use of next-generation sequencing (NGS) as a diagnostic instrument for critically ill neonatal and pediatric ICU patients in a Turkish hospital setting. Methods: Ten infants were enrolled based on predefined inclusion criteria, and trio RGS was performed. The mean age of the participants was 124 days, with congenital abnormalities being the most common indication for testing. Three patients had consanguineous parents. The mean turnaround time from enrollment to delivery of results was 169 h, with a diagnostic yield of 50%. Results: Three patients received a definitive molecular diagnosis, impacting their clinical management. Two patients benefited from the exclusion of Mendelian conditions, leading to alternative diagnoses. Discussion: This study demonstrates the feasibility and results of RGS in Turkish hospital settings, emphasizing the importance of timely genetic diagnosis in reducing the diagnostic odyssey for families and improving patient care. Further research is needed to evaluate the cost-effectiveness and applicability of RGS in the Turkish healthcare system for children with diseases of uncertain etiology.

Diagnostic Pitfalls of a Newborn with Congenital Nephrogenic Diabetes Insipidus.

Congenital nephrogenic diabetes insipidus (NDI) is a rare cause of hypernatremia in newborns. Central diabetes insipidus (CDI) is the main differential diagnosis of NDI. NDI responds poorly to desmopressin acetate (DDAVP) treatment while this is the mainstay of CDI management. Therefore, an early and correct diagnosis of NDI is crucial to avoid the complications of inappropriate therapy. Here, we report a newborn with hypernatremia and hypotonic polyuria. The patient was initially responsive but subsequently unresponsive to intranasal DDAVP treatment in regard to urine output and serum sodium levels. A novel hemizygous missense mutation (c.632T>C, p.L211P) in the AVPR2 gene was found both in the baby and his mother, and the diagnosis of congenital NDI was established. After hydrochlorothiazide treatment and hypo-osmolar formula were given, urine volume was decreased, and serum sodium levels were normalized. Early recognition and appropriate management of NDI can prevent complications of hypernatremic dehydration in young infants.

Two new patients with acromesomelic dysplasia, PRKG2 type-identification and characterization of the first missense variant.

Acromesomelic dysplasia, PRKG2 type (AMDP, MIM 619636), is an extremely rare autosomal recessive skeletal dysplasia characterized by severe disproportionate short stature presenting with acromesomelia, mild metaphyseal widening of the long bones and mild spondylar dysplasia. To date, only four variants have been reported; one nonsense, one splice-site, and two frameshifts in five AMDP families. Here, we report the first missense variant and a second splice-site variant in PRKG2 in two patients with clinical and radiological features of acromesomelic dysplasia. Furthermore, functional studies of the novel missense variant, p.Val470Gly, revealed that it was unable to down-regulate FGF2-induced MAPK signaling and, thus, would be predicted to cause growth delay. Hence, this report expands the mutational spectrum in skeletal dysplasias associated with PRKG2 variants. In addition, we propose recognizable facial features with acromesomelic dysplasia, PRKG2 type.

Clinical Heterogeneity and Different Phenotypes in Patients with SETD2 Variants: 18 New Patients and Review of the Literature.

SETD2 belongs to the family of histone methyltransferase proteins and has been associated with three nosologically distinct entities with different clinical and molecular features: Luscan-Lumish syndrome (LLS), intellectual developmental disorder, autosomal dominant 70 (MRD70), and Rabin-Pappas syndrome (RAPAS). LLS [MIM #616831] is an overgrowth disorder with multisystem involvement including intellectual disability, speech delay, autism spectrum disorder (ASD), macrocephaly, tall stature, and motor delay. RAPAS [MIM #6201551] is a recently reported multisystemic disorder characterized by severely impaired global and intellectual development, hypotonia, feeding difficulties with failure to thrive, microcephaly, and dysmorphic facial features. Other neurologic findings may include seizures, hearing loss, ophthalmologic defects, and brain imaging abnormalities. There is variable involvement of other organ systems, including skeletal, genitourinary, cardiac, and potentially endocrine. Three patients who carried the missense variant p.Arg1740Gln in SETD2 were reported with a moderately impaired intellectual disability, speech difficulties, and behavioral abnormalities. More variable findings included hypotonia and dysmorphic features. Due to the differences with the two previous phenotypes, this association was then named intellectual developmental disorder, autosomal dominant 70 [MIM 620157]. These three disorders seem to be allelic and are caused either by loss-of-function, gain-of-function, or missense variants in the SETD2 gene. Here we describe 18 new patients with variants in SETD2, most of them with the LLS phenotype, and reviewed 33 additional patients with variants in SETD2 that have been previously reported in the scientific literature. This article offers an expansion of the number of reported individuals with LLS and highlights the clinical features and the similarities and differences among the three phenotypes associated with SETD2.

A Case with Hypotrichosis-Lymphedema-Telangiectasia Syndrome with Hair Shaft Fragility.

Introduction: Hypotrichosis-lymphedema-telangiectasia syndrome (HLTS) is a disease characterized by the failure of angiogenesis, vascularization, and hair formation caused by a mutation in the SOX18 gene. Case Presentation: We report a 15-year-old female patient presented with sparse hairs on her scalp and eyebrows and the absence of eyelashes and body hair since birth. We detected premature weathering due to abnormality of the hair shaft. Discussion/Conclusion: Detection of trichophytosis and split hair in light microscopy in a patient with sparse hair, telangiectasia, and lymphedema may help diagnose HLTS.

Consistency of variant interpretations among bioinformaticians and clinical geneticists in hereditary cancer panels.

Next-generation sequencing (NGS) is used increasingly in hereditary cancer patients' (HCP) management. While enabling evaluation of multiple genes simultaneously, the technology brings to light the dilemma of variant interpretation. Here, we aimed to reveal the underlying reasons for the discrepancy in the evidence titles used during variant classification according to ACMG guidelines by two different bioinformatic specialists (BIs) and two different clinical geneticists (CGs). We evaluated final reports of 1920 cancer patients and 189 different variants from 285 HCP were enrolled to the study. A total of 173 of these variants were classified as pathogenic (n = 132) and likely pathogenic (n = 41) by the BI and an additional 16 variants, that were classified as VUS by at least one interpreter and their classification would change the clinical management, were compared for their evidence titles between different specialists. The attributed evidence titles and the final classification of the variants among BIs and CGs were compared. The discrepancy between P/LP final reports was 22.5%. The discordance between CGs was 30% whereas the discordance between two BIs was almost 75%. The use of PVS1, PS3, PP3, PP5, PM1, PM2, BP1, BP4 criteria markedly varied from one expert to another. This difference was particularly noticeable in PP3, PP5, and PM1 evidence and mostly in the variants affecting splice sites like BRCA1(NM_007294.4) c.4096 + 1 G > A and CHEK2(NM_007194.4) c.592 + 3 A > T. With recent advancements in precision medicine, the importance of variant interpretations is emerging. Our study shows that variant interpretation is subjective process that is in need of concrete definitions for accurate and standard interpretation.

COVID-19 PCR test performance on samples stored at ambient temperature.

The WHO-named Coronavirus Disease 2019 (COVID-19) infection had become a pandemic within a short time period since it was detected in Wuhan. The outbreak required the screening of millions of samples daily and overwhelmed diagnostic laboratories worldwide. During this pandemic, the handling of patient specimens according to the universal guidelines was extremely difficult as the WHO, CDC and ECDC required cold chain compliance during transport and storage of the swab samples. The aim of this study was to compare the effects of two different storage conditions on the COVID-19 real-time PCR assay on 30 positive nasopharyngeal and/or oropharyngeal samples stored at both ambient temperature (22 ± 2 °C) and +4 °C. The results revealed that all the samples stored at ambient temperature remain PCR positive for at least six days without any false-negative result. In conclusion, transporting and storing these types of swab samples at ambient temperature for six days under resource-limited conditions during the COVID-19 pandemics are acceptable.

Familial early-onset obesity in Turkish children: variants and polymorphisms in the melanocortin-4 receptor (MC4R) gene.

OBJECTIVES: Genetic factors have a key role in childhood obesity with higher rates in children than adults. Among the monogenic types of non-syndromic obesity, melanocortin-4 receptor (MC4R) deficiency is the most frequent cause. Beside pathogenic variants, single-nucleotide polymorphisms in MC4R gene are also associated with lower energy expenditure. The aim of this study was to estimate the frequency of MC4R variants and polymorphisms in a cohort of Turkish children and adolescents with severe early-onset obesity, and to understand the clinical features of patients. METHODS: Patients, 1-17 years of age, with the onset of obesity before 10 years of age and a body mass index (BMI) standard deviation score (SDS) of >2.3, and who had a family history of early-onset obesity in at least one of their first-degree relatives were included in the study. Beside routine blood tests genetic analyses for MC4R gene were performed. RESULTS: Analyses of MC4R revealed previously known variations in three (3.5%) patients, and pathogenic polymorphisms related with obesity in four (4.7%) patients. BMI SDS values were between 2.8 and 5.5 SDS in the pathogenic variant carrier group, and 2.8-4.9 SDS in the polymorphism group. Mean BMI SDS in variant-negative group was 3.4 ± 0.82. CONCLUSIONS: Investigation of the MC4R in individuals with early-onset obesity and presence of obesity first-degree relatives is important. Hypertension is a rare comorbidity compared to other causes. Contrary to studies reporting that insulin resistance was absent or very rare, we found it as a frequent finding in both pathogenic variants and polymorphisms of MC4R.