Wendy K. Chung

Phenotypes of Mouse diabetes and Rat fatty Due to Mutations in the OB (Leptin) Receptor

Mice harboring mutations in the obese (ob) and diabetes (db) genes display similar phenotypes, and it has been proposed that these genes encode the ligand and receptor, respectively, for a physiologic pathway that regulates body weight. The cloning of ob, and the demonstration that it encodes a secreted protein (leptin) that binds specifically to a receptor (OB-R) in the brain, have validated critical aspects of this hypothesis. Here it is shown by genetic mapping and genomic analysis that mouse db, rat fatty (a homolog of db), and the gene encoding the OB-R are the same gene.

Linkages and associations between the leptin receptor (LEPR) gene and human body composition in the Québec Family Study

OBJECTIVE: To investigate linkage and association between the leptin receptor (LEPR) gene and body composition variables in the Québec Family Study (QFS).DESIGN: Single-point linkage analysis using families, and covariance and chi-square analyses using normal weight and obese unrelated subjects from QFS.SUBJECTS: 169 nuclear families were used for linkage study. 308 unrelated subjects (146 males; 162 females) from these families were used for chi-square testing of genotype and allele distributions between subjects with body mass index (BMI) <27 kg/m2 (n=167) and those with BMI≥27 kg/m2 (n=141), and for a series of covariance analyses using age, plus height for fat mass (FM) and fat free mass (FFM), as covariates. A corrected P value (P*) for multiple tests has been calculated according to P*=1-(1-P)number of phenotypes.MEASUREMENTS: Variables were BMI (in kg/m2), sum of six skinfolds (SF6 in mm), FM (in kg), percent body fat (%FAT) and FFM (in kg). Polymerase chain react restricted fragment length polymorphisms PCR-RFLP) was used to identified a K109R substitution in exon 4, a Q223R in exon 6, a K656N in exon 14 and an automatic DNA sequencer for a CA microsatellite repeat in intron 3, and heteroduplex pattern on non-denaturing gel for a CTTT repeat in intron 16.RESULTS: Good evidence of linkage was observed for Q223R with FM (P=0.005; P*=0.02), and for the CTTT repeat with FFM (P=0.007; P*=0.03). Weaker linkages (0.02≤P≤0.05) were also observed between Q223R and BMI, SF6 and FFM, between the CA repeat and BMI, SF6 and FM, and between the CTTT repeat and FM. Moreover, FFM values were found to be different among genotypes for the CTTT repeat polymorphism with heavier females, carriers of the 123* allele at the CTTT repeat, showing 4 kg less of FFM (43.6±1.0, n=21 vs 47.7±0.8, n=30; P=0.005; P*=0.02) than non-carriers. Also, at the Q223R polymorphism, in lower BMI males, carriers of the Q223 allele were 4 kg lighter in FFM (53.4±0.6, n=47 vs 56.6±0.9, n=18; P=0.005; P*=0.02) than non-carriers. No significant differences were observed between lower and higher BMI subjects in genotype and allele frequency distributions for any of the polymorphisms.CONCLUSIONS: These results indicate that the LEPR gene is involved in the regulation of the body composition in human particularly of FFM in the QFS.

Exonic and Intronic Sequence Variation in the Human Leptin Receptor Gene (LEPR)

Increased adiposity is a major risk factor for cardiovascular disease and NIDDM (1). Genetic determinants of the degree of adiposity and body fat distribution have been demonstrated by twin and adoption studies, and the heritability (h) of obesity has been estimated to be as high as 0.90 (2). However, the major genes underlying the heritable contribution to body fatness in humans have remained elusive. Rodent models of genetically determined obesity provide excellent candidate genes for evaluation in humans. The linkage of obesity-related phenotypes in humans to genomic regions homologous to rodent leptin (Lep) (3) and leptin receptor (Lepr) (4,5) has been recently demonstrated. The recent cloning of Lepr, which is mutant in the diabetes (Lepr^) mouse and in fatty (Lepr) and Koletsky (Lepr) rats (6-9), the mapping of this gene (LEPR) to Ip32 in humans (10), and the description of the genomic structure of LEPR and two polymorphic intronic microsatellites (11) have provided the necessary reagents for the evaluation of LEPR in the genetics of human obesity. Because the phenotype associated with genetic defects in Lepr in Lepr/Lepr mice and Lepr/Lepr rats is profound early-onset obesity, we sought to identify allelic variations in LEPR, which may be responsible for the genetic variation in adiposity in humans. To maximize the likelihood of the detection of such sequence variants, we examined genomic DNA from a total of 229 obese and lean adults and children, ascertained in medical centers around the U.S. (New York, New York; New Orleans, Louisiana; and Huntington, West Virginia). The study sample was predominantly Caucasian, but also

The Gln 223 Arg and Lys 656 Asn Polymorphisms in the Human Leptin Receptor Do Not Associate With Traits Related to Obesity

T he Lepr/Lepr mouse is an autosomal recessive model of extreme obesity that phenotypically appears very similar to the Lepr/Lepr mouse, in which the leptin protein is absent (1). However, in the Lepr/Lepr mouse, the leptin protein is structurally normal (1). Leptin is ineffectual when injected into Lepr/Lepr mice, indicating that they are resistant to the action of this hormone (1). Recently, Lee et al. (2) and Chen et al. (3) demonstrated a point mutation in the leptin receptor of the Lepr/Lepr mouse that results in abnormal splicing of leptin receptor mRNA. Furthermore, studies of the leptin receptor in the Zucker fatty rat and the Koletsky rat have found mutations in the leptin receptor that also associate with extreme obesity (4,5). Although the leptin receptor has been identified in humans, its potential role in the development of obesity is still under investigation. In Pima Indians, a marker near the leptin receptor on chromosome 1 has been linked to acute insulin release (6). Considine et al. (7) studied leptin receptor cDNA in seven lean and eight obese subjects and found an adenosine-to-guanine substitution at nucleotide 861 that predicts a nonconservative substitution of glutamine to arginine at amino acid 223 (Gln^Arg) in the extracellular domain of the receptor. This amino acid substitution is at a site near the pathogenic mutation in the leptin receptor of the Zucker fatty rat, suggesting that this substitution may be clinically relevant. However, the GlnArg substitution did not associate with the obese phenotype in this small number of subjects (7). Additionally, in exon 12, a guanine-to-cytosine substitution was found at

Molecular Genetic Analysis of a Human Neuropeptide Y Receptor THE HUMAN HOMOLOG OF THE MURINE “Y5” RECEPTOR MAY BE A PSEUDOGENE

Neuropeptide Y is a 36-amino-acid peptide amide with numerous biological activities. These functions are mediated through several pharmacologically distinct receptors. To date five receptor subtypes have been cloned. Here we report the isolation, by low stringency homology cloning from a hypothalamic library, of a cDNA encoding the human homolog of the murine neuropeptide Y receptor subsequently reported (1). Translation of the human Y1-like receptor clone suggested that it encoded a receptor which is truncated in the third extracellular loop. Comparison of the human Y1-like sequence to that of the human Y1 receptor suggested that the truncated receptor could have resulted from a frameshift due to a single nucleotide deletion in the sixth transmembrane domain. Southern blot analysis suggested that the gene is single copy in the human genome. The gene is located on chromosome 5q. To test the hypothesis that allelic variation of nucleic acid length within the sixth transmembrane domain of the Y1-like receptor may exist to produce a functional receptor, genomic DNA from 192 individuals of various ages, ethnic backgrounds, and degrees of obesity were analyzed electrophoretically and by direct sequencing. No variation was detected in any of the subjects, indicating that this receptor subtype may be a transcribed pseudogene in humans.

Molecular Physiology of Monogenic and Syndromic Obesities in Humans

Obesity has become an increasingly prevalent public health problem and represents the complex interaction of genetic, developmental, behavioral, and environmental influences. Although rare, the study of monogenic forms of obesity provides insight into underlying molecular and physiologic mechanisms by which adiposity is regulated through food intake, energy expenditure, and partitioning of stored calories. The identification of the genetic basis for many forms of monogenic obesity has provided a group of candidate genes and molecular pathways for study of the genetic control of energy homeostasis. Many of the genes identified relate to the development and function of the hypothalamus and central control of food intake and energy homeostasis. Allelic variations in these genes could contribute to nonsyndromic forms of obesity.