Genetic association of PTPN22 polymorphisms with Type 1 diabetes in Pakistani children

1 Introduction

Type 1 Diabetes (T1D) is a chronic immune-mediated disease and is characterized by the damage of the endocrine pancreatic beta-cells, which results in insulin insufficiency and may induce early morbidities and mortality in children (Kiani et al., 2015). According to the International Diabetes Federation, the prevalence of T1D has increased from 5 % to 10 % of all cases of diabetes (Goyal et al., 2020). In Pakistan, less than 2 % of the T1D prevalence has been reported (Shera et al., 2008).

Environmental and genetic factors both have an impact on the development of T1D (Fung et al., 2009). There are more than 60 genes and loci have been linked to T1D (Xie et al., 2020). Genetic risk factors and susceptibility loci of T1D have been discovered by Genome-wide association studies (Storling et al., 2017) including INS, STAT4, CTLA-4, IL-2RA, PTPN22, and IFIH1 (Kiani et al., 2015). The PTPN22 gene is one of the strongest genetic candidate genesthat has been identified for T1D susceptibility and revealed a possible relationship with the clinical heterogeneity of the disease which makes it a potential therapeutic target (Prezioso et al., 2017).

The protein tyrosine phosphatase, non-receptor type 22 (PTPN22) is a powerful inhibitor of T-cell activation and negatively regulates the signaling of T or B-cell receptors (Welter et al., 2018). PTPN22 protein is expressed in many immune cells, such as T and B lymphocytes, dendritic, and natural killer cells. It is known as the third important genetic locus that increases the likelihood of developing T1D (Hasegawa et al., 2004) and other autoimmune disorders such as rheumatoid arthritis, Type 1 diabetes, and systemic lupus erythematosus, etc. (Namjou et al., 2013).

Several PTPN22 polymorphisms including rs1310182, rs1217414, rs33996649, rs1217419, rs2476601, and rs12760457 have been reported to be associated with T1D (Prezioso et al., 2017; kumar et al., 2014). Many studies have revealed that rs2476601 is found to be a significant SNP for T1D risk in the European (Smigoc Schweiger et al., 2019), Middle East (Sharma et al., 2021), and Asian populations (Pei et al., 2013). The rs2476601 SNP is a risk factor for various autoimmune diseases too (Dieude et al., 2008).

In Pakistan, the incidence of T1D doubled from the previous report (Condie et al., 2020). A genetic study was conducted in Pakistan to identify 32 T1D gene loci that had previously been reported in European populations (Kiani et al., 2015). However, the role of PTPN22 polymorphisms has not yet been investigated for their effects on T1D patients in the Pakistani population. Therefore, this study was designed to explore the role of PTPN22 polymorphisms of rs2476601, rs1310182, and rs1217414, and the susceptibility of T1D in Pakistani children.

2 Materials and methods

3 Results

In the current study, the average age of diagnosis of the T1D cases and control groups was 11.80 ± 6.46 and 11.58 ± 3.06, respectively (Table 1). The biochemical analysis revealed that participants with T1D had remarkably higher levels of fasting blood glucose (258.86 ± 130.86 vs. 87.12 ± 7.30; P < 0.001) and glycated hemoglobin (HbA1c) (11.51 ± 7.33 vs. 4.89 ± 0.39; P < 0.001) when compared to the control group. The analysis of clinical data was depicted in Fig. 1.

Close

Fig. 1

Clinical characteristics of T1D cases.

Export to PPT

4 Discussion

Type 1 Diabetes is a heterogeneous genetic disorder, multiple genes and their interactions are responsible for disrupting the mechanism of glucose metabolism. Since the PTPN22 gene is involved in immune cell signaling and regulation, consequently, genetic variation of the PTPN22 gene may contribute to the T1D pathogenesis (Blasetti et al., 2017). Previously, it is reported that polymorphisms of the PTPN22 gene are genetically associated with type 1 diabetes (Abbasi et al., 2017; Haider et al., 2018; Smigoc Schweiger et al., 2019). Therefore, this study was designed to investigate whether these polymorphisms (rs2476601, rs1217414, and rs1310182) were involved in increasing the risk of T1D or not among children.

In the present study, polyuria, polydipsia, joint pain, dizziness, and weight loss are the most common clinical features observed in affected children, and these symptoms are predominant in Asian and Middle Eastern populations, possibly due to a higher rate of consanguinity (Al-Yaarubi et al. 2014). Diabetic Ketoacidosis (DKA) is another severe and life-threatening complication that can result in death among children. The prevalence of DKA has been reported to vary widely, ranging from 10 % to 80 % in different populations (Shera et al., 2008; Al-Yaarubi et al., 2014). However, in Pakistani children, the frequency of ketoacidosis is comparatively low (3 %). One reason might be the deprived diagnostic facility and the unawareness of Pakistani parents.

This study showed that the AG genotype of rs2476601 of the PTPN22 gene showed a statistically significant (OR (95 % CI) = 0.95 (0.31–2.96); P < 0.02) association among T1D Pakistani children that might be involved with an increased risk of developing disease. A allele is found to be a risky allele (OR (95 % CI) = 0.53 (0.31–0.90); P < 0.02) for T1D development, which may be a consequence of dysregulation of the immune response, making beta cells more susceptible to the autoimmune attack (Blasetti et al., 2017). rs2476601 SNP has been identified as a pathogenic mutation (c.1858C > T) that encodes an amino acid substitution from arginine to tryptophan (R620W). This substitution disrupts the Lyp-Csk interaction, leading to reduced T-cell signaling and ultimately diminishing T-cell activation, which results in early-onset diabetes (Sharma et al., 2021). In addition, linkage disequilibrium analysis showed that rs2476601 SNP is the best candidate for T1D susceptibility in the European population (Smyth et al., 2008). However, no significant association is reported in China, and Japan, which may be due to heterogeneity between ethnic backgrounds (Pei et al., 2014; Taniyama et al., 2010). Additionally, several research studies have shown that rs2476601 plays an essential role in other autoimmune diseases (Piotrowski et al., 2008; Cinek et al., 2007).

TT genotypes of PTPN22 rs1310182 were significantly associated with increased T1D susceptibility (OR (95 % CI) = 0.53 (0.31–0.90); P < 0.02) that might affect its splicing mechanisms, leading to unusual PTPN22 expression contribute to T1D susceptibility. In the same way, the haplotypes of rs1310182 SNP are associated with T1D risk reported in the Japanese population (Taniyama et al., 2010) andother autoimmune disorders (Aflatounian et al., 2017).

AG and AA genotypes of rs1217414 were found to be aprotective variant against T1D risk. The findings of this study suggest that the intronic SNP (rs1217414) within the PTPN22 gene might potentially impact the splicing processes of PTPN22 leading to abnormal PTPN22 expression, potentially influencing the vulnerability to T1D. Although our data showed a significant association between the PTPN22 polymorphisms and T1D risk, extensive studies with large sample sizes of different ethnicities residing in different areas of Pakistan are required to detect the genetic variants impacting multifactorial traits of T1D in Pakistan.

5 Conclusion

The findings of this study revealed that the A allele of rs2476601 and the T allele of rs1310182 of the PTPN22 gene are significantly associated and have a high potential with the risk of T1D children. Results of this studymay help in a better understanding of T1D and will pave the way for improved detection and treatment to prevent complications related to T1D in children.