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Leukemia is a malignant hematologic disorder characterized by abnormal white blood cell differentiation leading to increased rates of cancer cells in the bone marrow and peripheral blood. It is a common malignancy that occurs in children and adults when changes occur in the regulatory processes of normal cells and cause uncontrolled proliferation of hematopoietic stem cells. in the bone marrow.The CDKN2B gene, which is located in chromosome 9P21, is a tumor suppressor gene that plays an important role in the cell cycle through its inhibition of cyclin complexes and cyclin dependent kinase 4/6, and the inactivation of this gene is due to mutations or by a process of methylation for promoter of gene leads to the occurrence of the disease.This study aims to determine the relationship between the genetic variation of the CDKN2B gene and the incidence of leukemia among children in the city of Mosul.This study included (71) children between the ages of (1-15) years old who were referred to Ibn Al-Atheer Hospital in the city of Mosul for a period ranging from September to October of 2022, and the samples were divided into two groups. The first included this category 20 children and counted As a control group, the second group included 71 children from among the children with leukemia. (5.0) ml of venous blood was drawn from the children and divided into three parts. The first part was placed in tubes containing EDTA anticoagulant, which is used for DNA extraction, and the second part was placed in Eppendorf tubes containing On trisol for the purpose of extracting the RNA, and the last part was placed in two gel tubes free of any anticoagulant substance to obtain blood serum. Determining the genetic variation of the CDKN2B gene using by analyzing the gene expression level of the CDKN2B gene based on the RT-PCR technique. also measured DNA methylation in the promoter of gene CDKN2B. In addition, the level of the cell cycle-regulating protein CDKN2B was measured based on ELISA technology. The results of the test for the DNA methylation process in the promoter of the CDKN2B gene showed that methylated DNA was present in all samples of the patients on whom the test was conducted at a rate of 100% compared to the control group in which there was no methylation of the studied gene primer, while the results showed the presence of bundles belonging to the unmethylated process in all samples Patients with healthy people by 100%, and if it is noticed that there is a decrease in the level of gene expression for patients compared to the control group, , as it was found A significant decrease in the level of CDKN2B protein at the level of probability p≤0.05, the ratio in the control group was 40.1 ± 2.34 compared to the patients group 28.5 ± 1.24.We conclude from this study that genetic variations and mutations and an increase in methylation led to a decrease in the level of gene expression of CDKN2B gene with A decrease in the level of the encoded protein, which is one of the main causes of the development of leukemia.