Abstract: 　Objective　To explore the clinical characteristics and pathogenic genes of activated PI3K-δ syndrome (APDS). Method 　The clinical data of APDS in a child was retrospectively analyzed. Results　A boy aged 3 years and 9 months presented recurrent respiratory infections, hepatosplenomegaly and growth retardation. The DNA was extracted from the peripheral blood of the child and his parents. The sequence analyses were performed by whole exome sequencing technology and the mutant gene was validated by Sanger sequencing. A novel heterozygous missense mutation (De novo), c.3061G>A (E1021K), was found in the PIK3CD gene in the child, and both his parents had normal genotypes. PIK3CD gain-of-function mutations leads to enhanced activity of the encoded p110δ. The PI3K-PIP3-AKT-mTOR signaling pathway is over-activated, which induces cell differentiation and proliferation, and thus the disease is caused. So the mutation is a pathogenic mutation. Conclusion　PI3K-δ overactivation syndrome is a rare autosomal dominant immunodeficiency disease, and genetic testing can assist the diagnosis.

Key words: activated PI3K-δ syndrome;　whole exome sequencing technology;　gene mutation