Screening of LEP gene polymorphisms as a risk factor for obesity and type 2 diabetes in Iraqis

Abstract

The prevalence of obesity and diabetes changes dramatically with lifestyle and unequal risk among individuals have made scientists interested to understand how the environment interferes with genetic factors to make it so-called genetic predisposition. This study aimed to explore wherethe most variable region is in leptin gene and analyse microsatellite repeats with direct sequencing in Iraqis and compare our alleles with other populations as a risk for obesity and T2D predisposition. DNA was extracted from blood of 60 type 2 diabetics and 70 non diabetics individuals, LEP 5‛UTR, exon 2 and 3 were screened in 45 individuals (24 type 2 diabetes patients and 21 non- diabetics), LEP TTTC repeats region were amplified in all 130 participants from which 22 control samples were purified and sequenced, superimposed sequences were analyzed manually. Sequencing results showed G>A polymorphism (rs2167270) in 5‛UTR region. No polymorphisms detected in LEP exons 2 and 3. LEP microsatellites alleles were classified depending on sizes into class1 < (220bp) and class2 (> 220bp). Analysis of 22 control samples sequences of microsatellite region resulted in 6 type1 allele (unique sequence) and 5 type 3 allele (13 different isoforms) depending on TTTC arrangement separated by Ts bases. We concluded that LEP variations were in non- coding regions and no significant difference was observed in allele frequency between both groups, but there was a huge diversity in microsatellite repeat number and context among individuals. This may affects gene function thus prepare a predisposition for obesity and type 2 diabetes.

Keywords: Iraq; Leptin; Obesity; Screening; Type 2 diabetes; ob gene.

Figure 1

Mixed sequence traces showing microsatellite repeats (TTTC)n and underlined downstream sequence. This figure represents heterozygous genotype which includes two alleles. Analysis of this sequence showed that one allele had additional two repeats (bold) than other.

Figure 2

Theoretical explanation of type 3 allele’s evolvement from type1 during genetic recombination process, both acceptor and donor are type1 alleles, deletion of repeats region and subsequently deteriorated by natural selection. Presence of TTTC3 in the end of repeats is an evidence of a very short allele, gradually disappeared or merged with other forms.