Dear editor, SINGLE-NUCLEOTIDE polymorphism (SNP) is one of the most common types of DNA sequence variants in human genome (1). Each SNP shows a difference in only one NUCLEOTIDE.More than 10 million SNPs are mapped in human genome, so in average, there is one SNP in every 300 NUCLEOTIDEs. SINGLE-NUCLEOTIDE POLYMORPHISMS can be located in coding or noncoding regions, within a gene or outside of it. As stated in the definition of polymorphism, SNPs are not involved in disease occurrence directly, but they could be disease-associated via their functions (2). In this regards, there is a definition for functional SNP when it is ascertained that the polymorphism has an influence on the gene function...

SINGLE NUCLEOTIDE polymorphism (SNP, pronounced snip) represents a DNA sequence variant of a SINGLE base pair with the minor allele occurring in more than 1% of a given population. The broad field of applications for SNPs induced a pressing need for effective instruments for SNP detection. During the last decade a considerable number of methods for SNP discovery (search for new SNPs) and detection (recognition of already known SNPs) were developed. Studying the association between quantitative phenotype and SNPs has been a major challenge in genetics. To understand underlying mechanisms of complex phenotypes, it is often necessary to consider joint genetic effects across multiple SNPs. In this article, SNPs and their role in association studies were reviewed.

Background: Juvenile systemic lupus erythematosus (JSLE) is a chronic, recurrent multisystem inflammatory disease, caused by a combination of environmental events and genetic risk factors. As cytokines, including interleukin-4 (IL-4), seem to have a role in the pathogenesis of JSLE, this investigation was performed to evaluate the associations of specific SINGLE-NUCLEOTIDE POLYMORPHISMS (SNPs) of IL-4 gene in a case control association study.Methods: Fifty nine patients with JSLE were recruited in this study as patients’ group and compared with 140 healthy volunteers. Genotyping was performed for IL-4 gene at positions -1098, -590 and -33, using polymerase chain reaction with sequence-specific primers method.Findings: Following alleles were found to be more common among patients with JSLE: C at -590 and -33 and T at -1098 of IL-4 gene (P<0.001; OR=4.6, P<0.001; OR=2.7, andP<0.001; OR=2.1, respectively). Moreover, frequency of following alleles were remarkably lower in patients with JSLE, in comparison with controls: T at -590 and -33 and G at -1098 of IL-4 gene (P<0.001; OR=0.2, P<0.001; OR=0.3, and P<0.001; OR=0.4, respectively).Additionally, significant positive associations for the following genotypes were recognized in JSLE cases, compared with controls: C/C and T/T at -33, C/C at -590 and T/T at -1098 of IL-4 gene (P<0.001; OR=5.3, P<0.02, P<0.001; OR=29.5, and P<0.001; OR=3.3, respectively), while following genotypes were less frequent among patients with JSLE: T/C at -33 and -590 and T/G at -1098 of IL-4 gene (P<0.001; OR=0.1, P<0.001; OR=0.03, and P<0.001; OR=0.3, respectively). Furthermore, we noticed an astonishing negative haplotypic association for JSLE for IL-4 (positions -1098, -509, -33) TTC, GCC, and TTT haplotypes (P<0.001). There was also a significant relationship between TCC haplotype (IL-4 gene at positions -1098, -590, -33) and having JSLE (P<0.001).Conclusion: Cytokine gene POLYMORPHISMS may influence susceptibility to JSLE. Particular IL-4 gene variants are associated with JSLE and might have a role in pathophysiology of disease.

Background: Interleukin-4 (IL-4) plays a critical role in forming the nature of immune responses. As of its importance in inhibiting the production of proinflammatory cytokines by monocytes and activated T cells, the IL-4 gene POLYMORPHISMS were investigated in a group of patients with febrile seizure (FS).Methods: Ninety patients with febrile seizure were enrolled in this study and compared with 140 controls. The allele and genotype frequency of 3 SINGLE NUCLEOTIDE POLYMORPHISMS (SNPs) within the IL-4 gene were determined.Findings: The frequency of the IL-4 -590/C allele in the patient group was significantly higher than in the control group (p<0.001). The most frequent genotypes in patients with febrile seizure were IL-4 (-33) CC (p<0.01), IL-4 (-1098) GT (p<0.046), IL-4 (-590) CC (p<0.001) and IL-4 (-33) TT (p<0.02). The frequency of the following genotypes was significantly lower in patients compared to controls: IL-4 (-590) TC (p<0.001) and IL-4 (-33) TC (p<0.001). The most frequent IL-4 haplotypes in the patient group, which were significantly higher than in the control group, were TCC (p<0.00), TCT (p<0.02), and GTC (p<0.02) haplotypes. In contrast, the frequencies of the following haplotypes in the patient group were significantly lower than the controls: GCC (p<0.01), TTT (p<0.009), and TTC (p<0.007).Conclusion: Certain alleles, genotypes, and haplotypes in IL-4 gene were overrepresented in patients with febrile seizure, which possibly could predispose individuals to this disease.

2Introduction: Human genome consists of the three billion base pairs that has about one percent of genetic variation from one person to another، which determines physical، psychological، and susceptibility to diseases. Among the types of genetic diversity, SINGLE NUCLEOTIDE POLYMORPHISMS are one of the most important genetic differences between two people. SINGLE NUCLEOTIDE polymorphism variation is located in the promoter region, exons، introns، untranslated regions and other Deoxyribonucleic acid (DNA) regions. While variation in the exon region can change susceptibility to diseases depending on whether it changes the protein structure or affects translation kinetics. Diversity in the promoter region can affect the interaction of genetic and epigenetic elements. Also، variation in the promoter region can affect the DNA methylation status. Polymorphic variation in the intron region can affect Messenger Ribonucleic acid splicing and the function of cis-regulatory elements. Polymorphic variation in the 5' Untranslated region، region causes a change in translation efficiency,، while a change in the 3' Untranslated region binds micro Ribonucleic acids to their position then affects the effects. In some cases، variations in Transfer Ribonucleic acid (tRNA) and Ribosomal ribonucleic acid (rRNA) affect the function of these regulatory cis elements. Conclusion: From a clinical point of view, a deep knowledge of this type of genetic variation can help the treatment process, manage patients and understand the prognosis based on these SNPs. Private or personalized medicine is also fundamentally based on genetic diversity. In this article, it was reviewed the types of SINGLE NUCLEOTIDE genetic variation and presented examples of types of cancer, neurological and immunological diseases.