HUMAN LEPTIN RECEPTOR GENE IN OBESE JAPANESE SUBJECTS - EVIDENCE AGAINST EITHER OBESITY-CAUSING MUTATIONS OR ASSOCIATION OF SEQUENCE VARIANTS WITH OBESITY

Leptin is an adipocyte-derived bloodborne satiety factor that acts on its cognate leptin receptor (Ob-R) in the hypothalamus, thereby regula ting food intake and energy expenditure. To explore whether mutations in the Ob-R gene cause obesity in humans, we have searched for mutatio ns in the gene for Ob-Rb, a biologically active receptor isoform, in o bese Japanese subjects. We have also examined associations between suc h mutants and obesity in the Japanese. Genomic DNAs were used as templ ates in polymerase chain reaction (PCR) with primers selected to ampli fy exons 2 to 20 of the human Ob-Rb gene. Direct sequence analysis of the PCR products revealed 7 nucleotide sequence variants (Lys109Arg, G ln223Arg, Ser343Ser, Ser492Thr, Lys656Asn, Ala976Asp, and Pro1019Pro) in the Ob-Rb coding region from 17 obese Japanese subjects with a fami ly history of obesity (BMI 39.3+/-8.4 kg/m(2)). No missense and nonsen se mutations were found such as those in Zucker fatty (fa/fa) rats and Koletsky (fa(k)/fa(k)) rats. Nucleotide substitutions occurred at rel atively high frequencies at codons 109, 223, 976, and 1019 (79, 91, 10 0, and 85 %, respectively). Allele frequency of each variant determine d by PCR-RFLP and PCR-single strand conformation polymorphism analyses showed no significant differences between 47 obese (BMI 35.1 +/- 6.5 kg/m(2)) and 68 non-obese (BMI 21.6 +/- 2.2 kg/m(2)) subjects. The pre sent study represents the first report of sequence variants of the Ob- Rb gene in the Japanese and provides evidence against either obesity-c ausing mutations or association of sequence variants with obesity in o bese Japanese subjects.