the investigators aim in this study to investigate the potential association of single gene polymorphisms of CTLA-4 (SNPs; rs: 3087243) using real-time PCR in children with primary ITP.

Primary immune thrombocytopenia (ITP) is an acquired autoimmune bleeding disorder characterized by isolated thrombocytopenia (platelet count < 100 × 109/L) in the absence of other etiologies. The incidence of the disease is approximately 2-10 per 100,000 adults each year, with a prevalence of 9-20 per 100,000 adults Auto antibody-mediated platelet destruction is the canonical mechanism of platelet destruction in ITP. Platelets coated by anti-glycoprotein (GP) autoantibodies are prematurely destroyed by macrophages via Fcγ receptors (FcγRs) in the reticuloendothelial system. Autoantibodies also accelerate platelet destruction through the induction of complement-dependent cytotoxicity (CDC) and platelet apoptosis Many studies have demonstrated that CD8+ cytotoxic T lymphocytes (CTLs) from peripheral blood or spleen of ITP patients can directly lyse platelets or induce platelet apoptosis through granzyme B and perforin. CTLs and anti-GP autoantibodies can induce the desialylation of platelet surface glycans, leading to premature platelet clearance.

The immune checkpoint pathways are critical modulators of the immune system, allowing immune response initiation and preventing autoimmunity onset. Immune checkpoints, including co-stimulation and co-inhibition signal pathways, are among the central mechanisms that regulate T-cell-mediated immune responses CTLA-4 production is strongly influenced by genetic factors. Single-nucleotide polymorphisms (SNPs) of the CTLA-4-encoding genes are involved in the pathogenesis of many autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) In recent years, it had been shown that thrombocytopenia was associated with the transcription level of CTLA4 and regulation of T-cell activation

Inclusion criteria: approval to sign an informed written consent, patient with newly diagnosed ITP, patient age > 1 year and < 18 years and both sexes are included.

Exclusion criteria:

Refusal to sign an informed written consent, patient with persistent ITP, patient with chronic ITP, patient with secondary immune thrombocytopenia and patient age < 1 year or > 18 years

1. Full history taking.
2. Through clinical examination.
3. Laboratory investigations:

a .Complete blood count with platelet indices: Mean Platelet Volume, Plateletcrit, platelet distribution width (MPV, PCT & PDW).

b. Genotyping of rs3087243-related single-nucleotide polymorphism.