Molecular investigation of genetic and environmental factors contributing to obesity in adolescent learners residing in the semi-urban/rural areas of the Western Cape Province, South Africa

Yako, Yandiswa Yolanda (2012-12)

Thesis (PhD)--Stellenbosch University, 2012.

Includes bibliography

Thesis

ENGLISH ABSTRACT: Background/Aims: Obesity has increased rapidly in South African children and adolescents with significant variability observed among racial groups. Genes that regulate appetite have been studied in different populations worldwide, but their role in obesity among South African adolescents is unknown. The present study aimed at investigating the role of these genes, and their combined effect with physical activity in the development of obesity among South African adolescents. Methods: A total of 1564 South African school learners of Caucasian (n= 146), Mixed Ancestry (n= 872) and Black African (n= 537) ethnic groups were recruited for a research project that aimed to elucidate diabetes and the metabolic syndrome in children and adolescents attending schools in periurban areas of the Western Cape. The present case-control study included 227 obese-overweight (115 Black Africans and 112 Mixed Ancestry), and 204 normal weight (94 Black Africans and 110 Mixed Ancestry) adolescents learners. The learners were genotyped for nine polymorphisms (LEP: 19G>A, Lys36Arg, Val94Met; LEPR: Lys109Arg; Gln223Arg, Lys656Asn; CART: c.160-33G>A, c.499delA, and c.517A>G; GHRL: Leu72Met; and MC3R: Thr6Lys, Val81Ile) using allele-specific restriction enzyme analysis and automated sequencing. Genotype and haplotype associations with anthropometric variables such as body mass index (BMI), waist, hip, and mid-upper-arm circumferences (WC, HC, MUAC), and metabolic traits (fasting blood glucose, high density lipoproteincholesterol, total cholesterol), and blood pressure were further conducted. Furthermore, the type and frequency of physical activity was assessed by means of structured questionnaires; and its effect on obesity-related variables investigated in learners that were genotyped for the MC3R Thr6Lys and Val81Ile polymorphisms. Results: In a stepwise backward logistic regression analysis (containing age, gender, and LEP, LEPR, CART and GHRL polymorphisms), CART c.517A>G was independently significantly associated with obesity (OR= 5.98; 95%CI= 2.02, 21.27). CART c.517G carriers had higher MUAC (b coefficient= 1.88; 95%CI= 0.31, 3.44) while the LEPR 109Arg allele was significantly associated with decreased BMI (b coefficient = -2.36; 95%CI= -4.24, -0.47), WC (b coefficient = -5.66; 95%CI= -9.89, -1.44) and MUAC (b coefficient = -1.61; 95%CI= -3.00, -0.22); after adjusting for age, gender, and ethnicity. The haplotype containing the three LEP polymorphisms (A-A-A compared to the reference G-A-G haplotype) increased BMI (p= 0.0155), MUAC (p= 0.0146), and HC (p= 0.0128). The minor alleles of the MC3R polymorphisms decreased BMI, HC, WC, MUAC and TC; whilst only the Thr6Lys was associated with systolic and diastolic blood pressure (p= 0.0047 and 0.0027, respectively) in Mixed Ancestry learners. Doing house chores was associated with lower total cholesterol, independently and in the presence of the 81Ile allele (b coefficient = -0.355; 95%CI= 0.148, 0.561). Conclusion: To our knowledge, this is the first study that reports CART c.517A>G polymorphism as a risk factor for obesity in adolescents. Furthermore, the present study demonstrated that the MC3R polymorphisms had a positive effect on total cholesterol, which was further enhanced in physically active individuals. Similar to other studies, LEPR Lys109Arg and LEP polymorphisms were associated with variations in obesity-related variables among Black African and Mixed Ancestry South African learners.

AFRIKAANSE OPSOMMING: Agtergrond/Doelwitte: Vetsug het drasties toegeneem in Suid-Afrikaanse kinders en adelossente met ‘n beduidende variasie opgemerk tussen verskillende rassegroepe. Gene verantwoordelik vir regulering van eetlus is reeds wêreldwyd in verskillende bevolkingsgroepe bestudeer, maar hul rol in oorgewig Suid-Afrikaanse adolessente is onbekend. Die huidige studie was daarop gerig om ondersoek in te stel na die rol van hierdie gene en hul gekombineerde effek met fisiese aktiwiteit in die ontwikkeling van vetsug onder Suid-Afrikaanse adolessente. Metodes: ‘n Totaal van 1564 Suid-Afrikaanse leerders van Kaukasiese Afkoms (n=146), Gemengde Afkoms (n=872) en Swart Afkoms (n= 537) was gewerf in die navorsingsprojek wat ten doel gehad het om kinders en adolosente met diabetes en die metaboliese sindroom te identifiseer wat skole bygewoon het in semi-voorstedelike gebiede van die Wes-Kaap. Die huidige gevalle studie het 227 vetsugtige-oorgewig (115 Swart Afkoms en 110 Gemengde Afkoms) en 204 normale gewig (94 Swart Afkoms en 110 Gemengde Afkoms) leerders ingesluit. Die leerders was gegenotipeer vir nege polimorfismes (LEP: 19G>A, Lys36Arg, Val94Met; LEPR: Lys109Arg; Gln223Arg, Lys656Asn; CART: c.160-33G>A, c.499delA, and c.517A>G; GHRL: Leu72Met; and MC3R: Thr6Lys, Val81Ile) met die gebruik van alleel-spesifieke restriksie ensiem analises en geoutomatiseerde DNA volgorde bepalings tegnieke. Genotipiese en haplotipiese assosiasies met antropometriese veranderlikes soos liggaamsmassa indeks (BMI), middel-, heup- en mid-boarm omtrek (WC, HC, MUAC), metaboliese tendense (vastende bloed glukose, hoë-digtheid lipoproteïen-cholesterol, totale cholesterol) en bloeddruk was ook uitgevoer. Die tipe en frekwensie fisiese aktiwiteit was geassesseer deur middel van gestruktureerde vraelyste; en die uitwerking daarvan op vetsugverwante veranderlikes ondersoek in leerders wat vir die MC3R Thr6Lys en Val81Ile polimorfismes gegenotipeer was. Resultate: Statistiese ontleding (‘‘stepwise backward logistic regression analysis”), wat ouderdom, geslag en polimorfismes (LEP, LEPR, CART GHRL) ingesluit het, het getoon dat CART c.517A>G betekenisvol onafhanklik geassosiasieer was met vetsug (OR= 5.98; 95% CI= 2.02, 21.27). CART c.517G draers het ‘n hoër MUAC waarde gehad (b koeffisient = 1.88; 95%CI= 0.31, 3.44), terwyl die LEPR 109Arg alleel betekenisvol geassosieer was met verlaagde BMI ((b koeffisient = -2.36; 95%CI= -4.24, -0.47), WC (b koeffisient = -5.66; 95%CI= -9.89, -1.44) en MUAC (b koeffisient = -1.61; 95%CI= -3.00, -0.22) na die aanpassing van ouderdom, geslag en etnisiteit. Die haplotipe met die drie LEP polimorfismes (A-A-A teenoor die G-A-G verwysingshaplotipe) het die BMI (p= 0.0155), MUAC (p= 0.0146) en HC (p= 0.0128) verhoog. Die mindere allele van die MC3R polimorfismes het die BMI, HC, WC, MUAC en TC verlaag; terwyl slegs die Thr6Lys polymorfisme met sistolies en diastolies bloeddruk (p= 0.0047 en p= 0.0027, onderskeidelik) geassosieer was in Gemengde Afkoms leerders. Die verrigting van algemene huistake was geassosieer met laer totale kolesterol vlakke, onafhanklik en in die teenwoordigheid van die 81lle alleel (b koeffisient= -0.355; 95%CI= 0.148, 0.561). Gevolgtrekking: Na ons wete is hierdie die eerste studie wat die CART c.517A>G polimorfisme as ‘n risikofaktor vir vetsug in adolessente aantoon. Die huidige studie toon ook dat die MC3R polimorfisme ‘n positiewe effek op totale kolesterol gehad het, wat ook verder versterk was in fisiese aktiewe individue. Soortgelyk aan ander studies, was die LEPR Lys109Arg en LEP polimorfismes geassosieer met variasies in vetsug-verwante veranderlikes onder Suid-Afrikaanse Swart en Gemengde Afkoms leerders.

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