ABSTRACT
BACKGROUND: Obesity is genetically heterogeneous and highly heritable, although polymorphisms explain the phenotype in only a small proportion of obese children. We investigated the presence of copy number variations (CNVs) in "classical" genes known to be associated with (monogenic) early-onset obesity in children. METHODS: In 194 obese Caucasian children selected for early-onset and severe obesity from our obesity cohort we screened for deletions and/or duplications by multiplex ligation-dependent probe amplification reaction (MLPA). As we found one MLPA probe to interfere with a polymorphism in SIM1 we investigated its association with obesity and other phenotypic traits in our extended cohort of 2305 children. RESULTS: In the selected subset of most severely obese children, we did not find CNV with MLPA in POMC, LEP, LEPR, MC4R, MC3R or MC2R genes. However, one SIM1 probe located at exon 9 gave signals suggestive for SIM1 insufficiency in 52 patients. Polymerase chain reaction (PCR) analysis identified this as a false positive result due to interference with single nucleotide polymorphism (SNP) rs3734354/rs3734355. We, therefore, investigated for associations of this polymorphism with obesity and metabolic traits in our extended cohort. We found rs3734354/rs3734355 to be associated with body mass index-standard deviation score (BMI-SDS) (p = 0.003), but not with parameters of insulin metabolism, blood pressure or food intake. CONCLUSIONS: In our modest sample of severely obese children, we were unable to find CNVs in well-established monogenic obesity genes. Nevertheless, we found an association of rs3734354 in SIM1 with obesity of early-onset type in children, although not with obesity-related traits.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/genetics , DNA Copy Number Variations , Obesity, Morbid/genetics , Overweight/genetics , Polymorphism, Single Nucleotide , Repressor Proteins/genetics , Thinness/genetics , Adolescent , Age of Onset , Case-Control Studies , Child , Child, Preschool , Cohort Studies , Humans , Infant , Obesity, Morbid/diagnosis , Overweight/diagnosis , Thinness/diagnosisABSTRACT
BACKGROUND: Variants in the melanocortin-4 receptor (MC4R) gene are the most frequent cause of monogenic obesity. The relevance of MC4R variations with respect to clinical phenotype and biochemical function remains controversial. METHODS: We sequenced the MC4R gene in 510 overweight/obese children. The clinical phenotype was assessed in a case-control setting matched for age, gender, puberty and body mass index. Identified MC4R variants were functionally characterized in vitro. RESULTS: The frequency of MC4R variants was 5.3%, with functionally relevant mutations (D(90)N, V(103)I/S(127)L, R(165)W, G(181)D) occurring in 1.2% (confidence interval 0.26-2.15) of our sample. 4.1% were carriers of variants (Y(35)Y, V(103)I, T(112)M, M(200)V, I(251)L) with preserved receptor function in vitro. We did not detect large heterozygous deletions by multiple-ligand probe amplification assay. There were no differences in anthropometric or metabolic parameters between children with loss-of-function mutations and noncarriers. Carriers of the V(103)I or I(251)L variant had higher high-density lipoprotein cholesterol and HbA1c levels than matched noncarriers of MC4R variants. CONCLUSIONS: In our data set of childhood obesity in central Germany, we identified functionally relevant mutations in the MC4R gene in only 1.2% of the children. There were no major significant phenotypic differences between obese children with and without MC4R mutations. Hence, the diagnosis of genetically caused obesity due to MC4R mutation should be made with caution.
Subject(s)
Obesity/genetics , Polymorphism, Single Nucleotide/physiology , Receptor, Melanocortin, Type 4/genetics , Adolescent , Age of Onset , Animals , COS Cells , Case-Control Studies , Child , Chlorocebus aethiops , Female , Gene Frequency , Genetic Predisposition to Disease , Genetic Variation/physiology , Germany/epidemiology , Humans , Male , Obesity/epidemiology , TransfectionABSTRACT
OBJECTIVE: Recent genome-wide association studies identified novel candidate genes for fasting and 2 h blood glucose and insulin levels in adults. We investigated the role of four of these loci (ADCY5, GIPR, GCKR and VPS13C) in early impairment of glucose and insulin metabolism in children. RESEARCH DESIGN AND METHODS: We genotyped four variants (rs2877716; rs1260326; rs10423928; rs17271305) in 638 Caucasian children with detailed metabolic testing including an oGTT and assessed associations with measures of glucose and insulin metabolism (including fasting blood glucose, insulin levels and insulin sensitivity/secretion indices) by linear regression analyses adjusted for age, sex, BMI-SDS and pubertal stage. RESULTS: The major allele (C) of rs2877716 (ADCY5) was nominally associated with decreased fasting plasma insulin (P = 0.008), peak insulin (P = 0.009) and increased QUICKI (P = 0.016) and Matsuda insulin sensitivity index (P = 0.013). rs17271305 (VPS13C) was nominally associated with 2 h blood glucose (P = 0.009), but not with any of the insulin or insulin sensitivity parameters. We found no association of the GIPR and GCKR variants with parameters of glucose and insulin metabolism. None of the variants correlated with anthropometric traits such as height, WHR or BMI-SDS, which excluded potential underlying associations with obesity. CONCLUSIONS: Our data on obese children indicate effects of genetic variation within ADCY5 in early impairment of insulin metabolism and VPS13C in early impairment of blood glucose homeostasis.