Evaluation of a Role for NPY and NPY2R in the Pathogenesis of Obesity by Mutation and Copy Number Variation Analysis in Obese Children and Adolescents.

Neuropeptide Y (NPY) and its G protein-coupled NPY Y2 Receptor (NPY2R) are highly expressed in orexigenic NPY/Agouti-related peptide neurons within the arcuate nucleus, a major integrator of appetite control in the hypothalamus. As NPY and NPY2R are interesting candidate genes for obesity, we hypothesized that a genetic variation in these genes might be implicated in the pathogenesis of obesity. In the first part of this study, we performed a mutation analysis of the coding region of NPY and NPY2R with high-resolution melting curve analysis. For the highly conserved NPY gene, an extended population of 436 obese children and adolescents was screened, while for NPY2R, a smaller subset of 306 patients was used. A control population of 300 healthy individuals was screened for NPY2R to determine the general prevalence of the variants found among patients. Direct sequencing was performed for samples with melting patterns deviating from wild-type. In the second part of this study, Multiplex Amplicon Quantification (MAQ) analysis was performed in 308 obese children and adolescents to detect copy number variation (CNV) in the NPY2R region. Mutation analysis of the NPY gene led to the identification of one common missense variant (L7P; MAF 0.04), while the screening of the NPY2R gene resulted in the identification of one rare missense variant F87I in the patient population. In our CNV analysis, we could not identify copy number variation in the NPY2R region among obese children and adolescents. In summary, this study clearly indicates that genetic variation in NPY and NPY2R is at low frequency and thus does not make a major contribution to the obese phenotype in the general population.

Copy number variation (CNV) analysis and mutation analysis of the 6q14.1-6q16.3 genes SIM1 and MRAP2 in Prader Willi like patients.

BACKGROUND: Prader-Willi syndrome (PWS), caused by a paternal defect on 15q11.2-q13, is the most common form of syndromic obesity. However, patients clinically diagnosed with PWS do not always show this defect on chromosome 15q and are therefore molecularly categorized as Prader Willi like (PWL). Deletions at 6q14.1-q16.3 encompassing MRAP2 and SIM1 were reported in some individuals with a PWL phenotype. In addition, a few mutations in SIM1 and MRAP2 were also previously identified in cohorts of obese individuals. Therefore, we decided to perform copy number variation analysis of the 6q14.1-6q16.3 region followed by mutation analysis of SIM1 and MRAP2 in a PWL cohort. METHODS: A genome-wide microarray analysis was performed in a group of 109 PWL patients. Next, we screened 94 PWL patients for mutations in SIM1 and MRAP2 using high-resolution melting curve analysis and Sanger sequencing. Additionally, 363 obese children and adolescents were screened for mutations in MRAP2. RESULTS: No gene harboring deletions were identified at the 6q14.1-q16.3 region in the 109 PWL patients. SIM1 mutation analysis resulted in the identification of one very rare nonsynonymous variant p.P352S (rs3734354). Another rare nonsynonymous variant, p.A40S, was detected in the MRAP2 gene. No variants were identified in the 363 obese individuals. CONCLUSIONS: In contrast to literature reports, no gene harboring deletions were identified in the SIM1 and MRAP2 regions in our PWL cohort. Secondly, taking into account their very low minor allele frequencies in public sequencing databases and the results of in silico prediction programs, further functional analysis of p.P352S found in SIM1 and p.A40S found in MRAP2 is useful. This would provide further support for a possible role of SIM1 and MRAP2 in the pathogenesis of the PWL phenotype albeit in a limited number of patients.

Nucleotide variation of sFRP5 gene is not associated with obesity in children and adolescents.

Because sFRP5 was shown to be an important extracellular modulator of the Wnt pathway, regulating adipogenesis, we wanted to investigate the role of sFRP5 variants in human, monogenic obesity by performing mutation analysis. We screened the complete sFRP5 coding region in 622 obese children and adolescents and 503 lean control individuals by high-resolution melting curve analysis and direct sequencing. We found a total of 15 sequence variants in sFRP5, 10 of which resulted in a non-synonymous amino acid change. Five of these variants were, to our knowledge, not previously reported. For one of the variants (c.-3G>A), we identified a trend towards association between the variant frequency and the obese phenotype. We argue that, when looking at conservation and location inside known protein domains, several of the identified variants (D103N, A113V, K212N and H317L), may affect sFRP5 protein function. In addition, we found c.-3G>A, residing in the Kozak sequence, with a lower frequency in cases compared to controls. However, functional studies investigating the effect of sFRP5 variants on protein function are necessary to determine the true role of sFRP5 genetic variation in human, monogenic obesity.

Detection of a case of chronic myeloid leukaemia with deletions at the t(9;22) translocation breakpoints by a genome-wide non-invasive prenatal test.

OBJECTIVE: Non-invasive prenatal tests (NIPTs) interrogating the complete genome are able to detect not only fetal trisomy 13, 18 or 21 but additionally provide information on other (sub)chromosomal aberrations that can be fetal or maternal in origin. We demonstrate that in a subset of cases, this information is clinically relevant and should be reported to ensure adequate follow-up. METHOD: Genome-wide NIPT was carried out and followed by a software analysis pipeline optimized to detect subchromosomal aberrations. RESULTS: The NIPT profile showed deletions on chromosomes 9 and 22: NIPT 9q33.3q34.12(129150001-133750000)x1,22q11.23(23550001-25450000)x1,22q13.1(37850001-39600000)x1. This result was confirmed by single nucleotide polymorphism array on maternal genomic DNA, which also demonstrated that the deletions were somatic in nature. Fluorescence in situ hybridization and quantitative real-time polymerase chain reaction revealed that the deletions were flanking the translocation breakpoint on the derivative chromosome 9 as the result of a t(9;22)(q34;q11.2) translocation with BCR-ABL1 fusion typical for chronic myeloid leukaemia (CML). Multidisciplinary counselling, together with complete blood count, taught that the woman was in an early chronic phase CML. The woman was followed up closely, and treatment could be postponed until after delivery. CONCLUSION: Genome-wide NIPT identified a CML in chronic phase caused by the typical t(9;22)(q34;q11.2) translocation and accompanied by deletions flanking the translocation breakpoints. © 2016 John Wiley & Sons, Ltd.

Genetic and structural variation in the SH2B1 gene in the Belgian population.

OBJECTIVE: Animal studies, genome-wide association and genomic structural variation studies have identified the SH2B1 gene as a candidate gene for obesity. Therefore, we have designed an extensive mutation and copy number variation (CNV) analysis investigating the prevalence of genetic and structural variations in SH2B1 in the Belgian population. DESIGN AND METHODS: In the first part of this study, we performed a mutation screen for variants in the SH2B1 coding region in 581 obese children and adolescents and 433 healthy, lean individuals with high-resolution melting curve analysis followed by direct sequencing. In the second part of this study, Multiplex Amplicon Quantification (MAQ) analysis was used to identify CNVs in the distal SH2B1-containing chr.16p11.2 region in 421 obese children and adolescents with no developmental delay or behavioral phenotype. RESULTS: Mutation analysis resulted in the identification of fifteen rare non-synonymous heterozygous variants. Several of these were found both in lean and obese subjects, suggesting that these are neutral polymorphisms. However, six private, heterozygous, non-synonymous variations were present in obese children only. Furthermore, we also identified six missense variants solely in lean individuals. CNV analysis could not identify carriers of the distal 16p11.2 deletion in our population. CONCLUSION: Our mutation analysis has demonstrated that variation in the SH2B1 gene is frequent in both lean and obese groups, with distinctive variations being present on either side of the weight spectrum. Although the equal variation frequency does not immediately support disease causality, it cannot be excluded that some variations are weight-increasing or -decreasing. Further functional testing of the variants will be necessary to fully understand the impact of these variants on SH2B1. We were not able to detect carriers of the distal 16p11.2 deletion in our study population. As we excluded patients with developmental or behavioral problems, we suggest that in addition to obesity, the distal deletion might predispose for these traits. Further characterization of the phenotype is therefore necessary to clearly identify the phenotype of the distal 16p11.2 microdeletion syndrome.

Resistin polymorphisms show associations with obesity, but not with bone parameters in men: results from the Odense Androgen Study.

Resistin is an obesity-related adipokine which has also been implicated in bone metabolism. Therefore, we designed a study to investigate the possible role of resistin gene variation in both obesity and bone mineral density. We included 1,155 individuals from the Odense Androgen Study (663 young subjects and 492 older subjects), a population-based, prospective, observational study on the inter-relationship between endocrine status, body composition, muscle function, and bone metabolism in men, in an association study with resistin (RETN) polymorphisms. Three RETN variants (rs1862513, rs3745367 and rs3745369) were genotyped with TaqMan Pre-Designed Genotyping assays. Linear regression was performed to investigate the possible association of these variants with several obesity- and bone-related parameters. After genotyping 1,155 Danish men, 663 young subjects and 492 older subjects, we found that rs3745367 was associated with several obesity-related measures in both the young and elderly cohort. Rs3745369 was only associated with obesity-phenotypes in the elderly cohort. When studying the combined cohorts, we could confirm the associations of rs3745367 with several obesity-related parameters. We were unable to identify any association between RETN polymorphisms and bone-related measurements. Together, these results illustrate resistin's role in the development of obesity. Rs3745367 gives the most consistent results in the current study and these should be confirmed in other populations. Research into its possible functional effect might also be required. A role for RETN variants in determining bone mineral density seems unlikely from our results.

No important role for genetic variation in the Chibby gene in monogenic and complex obesity.

Chibby (CBY) has been identified as a potent proadipogenic factor required for adipocyte differentiation. It has been shown that CBY inhibits the canonical Wnt pathway, and therefore promotes the development of new fat cells. Our objective therefore is to investigate the contribution of rare and common genetic variation in CBY to the development of human obesity. A mutation analysis was performed on a total of 566 obese patients and 432 lean individuals. To investigate the involvement of CBY in complex obesity, we performed a genetic association analysis of the entire CBY gene region on 1,011 obese individuals and 523 control samples. Four rare, novel variants were identified in either obese patients or lean control subjects, among which two non-synonymous variations and one frameshift mutation. In addition, four previously reported CBY variants were found. In the association analysis, logistic and linear regression showed no association between common genetic variation in CBY and obesity parameters. Several novel variations were found, but no definite role in the pathogenesis of obesity could be confirmed. Results from the association analysis suggest that common variation in CBY is not a cause for obesity in the Belgian population.

Monogenic and complex forms of obesity: insights from genetics reveal the leptin-melanocortin signaling pathway as a common player.

The role of genetic factors involved in the etiology of human obesity is beyond question. The identification of the hypothalamic leptin-melanocortin signaling pathway as a critical regulator in energy homeostasis and food intake has been essential for genetic research. In this review, we discuss the involvement of established and novel genes from this pathway in the pathogenesis of obesity. Their roles in monogenic and complex forms of obesity are illustrated by discussing the results of mutation analysis, candidate gene and genome-wide association studies, as well as copy number analysis. While we can conclude from these outcomes that the leptin-melanocortin pathway is of immense importance, there is still a lot of heritability that currently cannot be explained. Future studies implementing genome-wide association studies, genome-wide copy number variant analysis, and whole exome and whole-genome sequencing might aid in finding new variation in the conventional pathways and might reveal new biological pathways implicated in the pathogenesis of obesity.

Identification of mutations in the NUCB2/nesfatin gene in children with severe obesity.

Nesfatin-1 is the N-terminal fragment of nucleobindin-2 (NUCB2) that was identified as a novel satiety molecule in rodents. The protein is reported to exert anorexigenic effects and appears to play an important role in hypothalamic pathways regulating energy homeostasis and food intake. In this study, we hypothesized that mutations in the nesfatin encoding gene NUCB2 might cause obesity in humans. Therefore, we screened the entire coding region of the NUCB2 gene for mutations in a population of 471 obese children and adolescents. Mutation analysis of NUCB2 identified a total of seven sequence variants of which four were previously reported as polymorphisms. The remaining three variants included ex9+6G>C, L125H and K178X and were found in 3 unrelated individuals in the obese population only (0.6%). Biochemical experiments including ELISA and western blot were performed on plasma samples of the obese patient carrying the nonsense mutation K178X. However, neither NUCB2/nesfatin-1 immunoreactive plasma levels of the patient, nor expression of full length NUCB2 differed significantly from matched obese control individuals. In conclusion, we have identified the first genetic variants in the NUCB2 gene in obese individuals, although further functional characterization will be essential to verify disease causality of the mutations.

The neurology of carbonic anhydrase type II deficiency syndrome.

Carbonic anhydrase type II deficiency syndrome is an uncommon autosomal recessive disease with cardinal features including osteopetrosis, renal tubular acidosis and brain calcifications. We describe the neurological, neuro-ophthalmological and neuroradiological features of 23 individuals (10 males, 13 females; ages at final examination 2-29 years) from 10 unrelated consanguineous families with carbonic anhydrase type II deficiency syndrome due to homozygous intron 2 splice site mutation (the 'Arabic mutation'). All patients had osteopetrosis, renal tubular acidosis, developmental delay, short stature and craniofacial disproportion with large cranial vault and broad forehead. Mental retardation was present in approximately two-thirds and varied from mild to severe. General neurological examinations were unremarkable except for one patient with brisk deep tendon reflexes and two with severe mental retardation and spastic quadriparesis. Globes and retinae were normal, but optic nerve involvement was present in 23/46 eyes and was variable in severity, random in occurrence and statistically correlated with degree of optic canal narrowing. Ocular motility was full except for partial ductional limitations in two individuals. Saccadic abnormalities were present in two, while half of these patients had sensory or accommodative strabismus, and seven had congenital nystagmus. These abnormalities were most commonly associated with afferent disturbances, but a minor brainstem component to this disorder remains possible. All internal auditory canals were normal in size, and no patient had clinically significant hearing loss. Neuroimaging was performed in 18 patients and repeated over as long as 10 years. Brain calcification was generally progressive and followed a distinct distribution, involving predominantly basal ganglia and thalami and grey-white matter junction in frontal regions more than posterior regions. At least one child had no brain calcification at age 9 years, indicating that brain calcification may not always be present in carbonic anhydrase type II deficiency syndrome during childhood. Variability of brain calcification, cognitive disturbance and optic nerve involvement may imply additional genetic or epigenetic influences affecting the course of the disease. However, the overall phenotype of the disorder in this group of patients was somewhat less severe than reported previously, raising the possibility that early treatment of systemic acidosis with bicarbonate may be crucial in the outcome of this uncommon autosomal recessive problem.

Rare Heterozygous PCSK1 Variants in Human Obesity: The Contribution of the p.Y181H Variant and a Literature Review.

Recently, it was reported that heterozygous PCSK1 variants, causing partial PC1/3 deficiency, result in a significant increased risk for obesity. This effect was almost exclusively generated by the rare p.Y181H (rs145592525, GRCh38.p13 NM_000439.5:c.541T>C) variant, which affects PC1/3 maturation but not enzymatic capacity. As most of the identified individuals with the heterozygous p.Y181H variant were of Belgian origin, we performed a follow-up study in a population of 481 children and adolescents with obesity, and 486 lean individuals. We identified three obese (0.62%) and four lean (0.82%) p.Y181H carriers (p = 0.506) through sanger sequencing and high resulting melting curve analysis, indicating no association with obesity. Haplotype analysis was performed in 13 p.Y181H carriers, 20 non-carriers (10 with obesity and 10 lean), and two p.Y181H families, and showed identical haplotypes for all heterozygous carriers (p < 0.001). Likewise, state-of-the-art literature concerning the role of rare heterozygous PCSK1 variants implies them to be rarely associated with monogenic obesity, as first-degree carrier relatives of patients with PC1/3 deficiency are mostly not reported to be obese. Furthermore, recent meta-analyses have only indicated a robust association for scarce disruptive heterozygous PCSK1 variants with obesity, while clinical significance is less or sometimes lacking for most nonsynonymous variants.

Association between polymorphisms of the Nesfatin gene, NUCB2, and obesity in men.

Nesfatin-1, which originates from its precursor protein nucleobindin-2 (NUCB2), is a novel appetite-regulating molecule that might be associated with the melanocortin signalling pathway in the hypothalamus. The secreted protein appears to play an important role in metabolic control through its anorexigenic and anti-hyperglycemic effects. Therefore, we hypothesized that polymorphisms in the NUCB2 gene might influence the susceptibility for the development of obesity. In this study, we investigated the association of NUCB2 polymorphisms with the development of obesity in an extensive Caucasian population comprising 1049 obese subjects and 315 normal weight control individuals. We selected 8 tagSNPs, which after additional analysis of 6 multi-marker tests, cover most information on common genetic variation in the selected region. We found association with obesity for 3 SNPs (rs1330, rs214101 and rs757081) and 3 multi-marker tests, only when analyzing the male population separately. We subsequently performed linear regression analysis, again in the male population only, and found that several SNPs were associated with BMI, weight and fat free mass. These data indicate that polymorphisms in the NUCB2 gene could play an important role in the protection against the development of obesity in male subjects and might have an influence on energy homeostasis. Nevertheless, further research including replication of our results and elucidation of the molecular mechanism remains necessary.

Association study of MC4R with complex obesity and replication of the rs17782313 association signal.

Recently, genome-wide association studies have discovered several single nucleotide polymorphisms (SNPs) involved in the etiology of complex obesity. A variant downstream from the melanocortin-4 receptor gene (MC4R), a gene known to be involved in monogenic obesity, was reported to be highly associated with BMI. In the present study, we performed a replication study with the previously reported SNP rs17782313. We also included 3 tagSNPs (rs8087522, rs11872992, and rs1943226) for the MC4R gene region in our study to understand the role of this gene in complex obesity. We genotyped all 4 SNPs in a population of 1049 obese cases (mean BMI=38.2±6.2) and 312 healthy lean individuals (mean BMI 22.0±1.7). We could confirm that rs17782313 is highly associated with complex obesity in our population (odds ratio=1.42, 95% CI 1.14-1.77, P=0.002). Furthermore, we found this SNP to be associated with BMI (B=0.92, 95% CI 0.19-1.65, P=0.01) and body weight (B=2.44, 95% CI 0.28-4.60, P=0.03). In addition, we could also detect an association between rs11872992 and complex obesity (odds ratio=0.74, 95% CI 0.57-0.98, P=0.03). Through conditional analysis, we demonstrate that this effect is independent from the rs17782313 association signal. No associations with obesity could be found for rs8087522 and rs1943226. In conclusion, we could replicate the previously reported association between rs17782313 and complex obesity. Furthermore, our data do not support the hypothesis that a SNP in MC4R causes the rs17782313 association signal.

Nonmosaic Isodicentric Y Chromosome: A Rare Cause of Azoospermia- From Genetics to Clinical Practice.

Azoospermia is diagnosed when no spermatozoa can be detected after centrifugation of seminal fluid on at least two separate occasions. A number of genetic disorders can be related to nonobstructive azoospermia, and in up to 15% of azoospermic males, a genetic disorder is diagnosed. A 36-year-old male with nonobstructive azoospermia was referred to our department of diabetes and endocrinology due to an aberrant testicular biopsy. The biopsy showed a disrupted spermatogenesis with a maturation arrest at the spermatocyte level in most tubuli seminiferi while others showed a Sertoli cell-only syndrome. Screening for Y chromosome microdeletions on peripheral blood using molecular analysis detected a terminal deletion of AZFbc. The result of karyotyping and fluorescence in situ hybridization (FISH) described an isodicentric Y chromosome with karyotype 46,X,idic(Y)(q11.22). Based on this case and the current available literature, we conclude that performing a testicular biopsy in patients with a nonmosaic idic(Y)(q) is not meaningful and that the prognosis on infertility is poor. Biological fatherhood is extremely unlikely in these patients, and proper counselling should be provided.

The role of the leptin-melanocortin signalling pathway in the control of food intake.

Obesity is one of the most important health problems today. Obesity is mostly caused by a complex interaction between environmental and genetic factors. However, several monogenic forms of obesity also exist. The mutations causing these forms of obesity were all found in genes involved in the leptin-melanocortin pathway: leptin, leptin receptor, proopiomelanocortin, prohormone convertase 1, and melanocortin-4 receptor. Recently, several novel players with a role in this pathway have been identified and have increased our knowledge on the regulation of food intake. These include the melanocortin-3 receptor, BDNF, SIM1, and nesfatin-1. In this review, we will discuss the most important players involved in this pathway. We will focus on genetic studies concerning mouse models involving these genes and reported human variation in these genes. We intend to provide an extensive overview of all currently known proteins with a significant role in this pathway. Together, these data demonstrate the importance of this pathway in the regulation of food intake and the pathogenesis of obesity.

Association study and mutation analysis of adiponectin shows association of variants in APM1 with complex obesity in women.

We performed an association study and mutation analysis of the adiponectin (APM1) gene to study its involvement in the development of obesity. We also studied the interaction with peroxisome proliferator-activated receptor gamma (PPARgamma). 223 obese women and 87 healthy female control subjects were used for association analysis. Mutation analysis was done on 95 morbidly obese adults and 123 overweight and obese children and adolescents. We selected 6 haplotype tagging SNPs in APM1 and the Pro12Ala variant (rs1805192) in PPARgamma to study the interaction. The G allele of rs2241766 was more common in controls (cases 10.8% vs. controls 18.4%, nominal p = 0.011; OR = 0.57, nominal p = 0.018). The rs2241766/rs3774261 haplotype was also associated with obesity (nominal p = 0.004). Only the latter association remained significant after controlling for the False Discovery Rate. Resequencing of exon 2, exon 3 and intron 2 in 95 individuals did not reveal any SNPs in high linkage disequilibrium with rs2241766. No interaction with the Pro12Ala variant in PPARgamma was detected. Mutation analysis of APM1 did not identify mutations. In conclusion, we found an association of an APM1 haplotype with obesity and found that APM1 mutations are not a common cause of monogenic obesity in our cohort.

Association of SIRT1 gene variation with visceral obesity.

The sirtuin SIRT1 is an important regulator of energy metabolism through its impact on glucose and lipid metabolism and therefore we tested the hypothesis that genetic variation in SIRT1 may have an effect on adiposity in a Belgian case/control association study. This study included 1,068 obese patients (BMI > or = 30 kg/m(2)) from the outpatient obesity clinic and 313 lean controls (BMI between 18.5 and 25 kg/m(2)). Anthropometrics were assessed by classical methods and visceral (VFA), subcutaneous (SFA) and total abdominal (TFA) fat areas were determined by a CT scan. The extent of linkage disequilibrium in SIRT1 allowed us to reduce the number of SNPs to two, sufficient to cover the entire gene. The two tagSNPs (rs7069102 and rs3818292) were analyzed by LightSNiP assays in all subjects. Rs3818292 genotypes were similarly distributed in cases and controls, whereas rs7069102 was different for the additive (P = 0.007) and dominant (P = 0.01) model. The variant C-allele of rs7069102 reduced obesity risk with an OR of 0.74 (P = 0.025; 95% CI 0.57-0.96) under a dominant model. In obese male subjects, this variant allele was associated with increased waist circumference (P = 0.04), WHR (P = 0.02), TFA (P = 0.03) and VFA (P = 0.005) (dominant model; adjusted for age and BMI). Rs3818292 was related to VFA (P = 0.005; adjusted for age and BMI) in obese males while in obese women, no significant associations were detected. Our data suggest that genetic variation in SIRT1 increases the risk for obesity, and that SIRT1 genotype correlates with visceral obesity parameters in obese men.

Association of the BDNF Val66Met variation with obesity in women.

Brain-derived neurotrophic factor (BDNF) has been implied in the regulation of food intake. In the present study, we genotyped the Val66Met polymorphism in a Belgian cohort of 532 obese women and 197 healthy female controls and were, for the first time, able to show an association of the 66Met allele with obesity, at least in our female cohort.

Variants in the FTO gene are associated with common obesity in the Belgian population.

Three independent studies, of which two genome-wide scans, have reported an association between SNPs in the FTO (Fat mass and obesity associated) gene and obesity, in different European cohorts. We selected the SNPs with the strongest evidence for association from the first two studies and genotyped 1099 obese patients and 268 healthy control individuals. Both SNPs were significantly associated with obesity, enabling us to replicate earlier findings from Caucasian cohorts in a Belgian population sample.

CNV analysis and mutation screening indicate an important role for the NPY4R gene in human obesity.

OBJECTIVE: Genome-wide copy number variation (CNV) analyses have associated the 10q11.22 CNV with obesity. As the NPY4R gene is the most interesting candidate gene in this region, it was hypothesized that both genetic and structural variation in NPY4R might be implicated in the pathogenesis of obesity. METHODS: In the first part of this study, 326 children and adolescents with obesity and 298 healthy lean individuals were screened for CNV in the NPY4R-containing chr.10q11.22 region. In the second part of this study, a mutation screen for variants in the NPY4R coding region was performed in 356 children and adolescents with obesity and 337 healthy lean adults. RESULTS: Our CNV analysis demonstrated a significantly higher frequency of NPY4R containing 10q11.22 CNV loss in the patient population (P = 0.0003), while CNV gain in this region was more prevalent in the control population (P = 0.031). Mutation analysis resulted in the identification of 15 rare non-synonymous heterozygous variants. For two variants that could only be identified in the patient population, receptor dysfunction and thus a pathogenic effect were demonstrated. CONCLUSIONS: In conclusion, these data support an essential role for genetic and structural variation within the NPY4R gene in the pathogenesis of obesity.