Serine/Threonine Kinase 4 Deficiency Caused by a Potential Novel c.248del, p.Pro83Leufs∗3 Mutation: A Case Report.

BACKGROUND: Serine/threonine kinase 4 (STK4) deficiency is one of the rare causes of combined immunodeficiency (CID). In this study, we report a novel mutation causing STK4 deficiency, which presents with chronic pyelonephritis, an uncommon presentation. CASE PRESENTATION: A 10-year-old female with an incidental mass in the kidney extending to the liver, night sweats, and fever was presented. To reduce the mass effect and rule out the possibility of malignancy, the patient underwent a nephrectomy, and a biopsy revealed chronic pyelonephritis. After surgery, due to the persistent leukopenia, the chance of an inborn error of immunity was considered. The patient was referred to the immunology clinic. INVESTIGATIONS: Immunophenotyping revealed low levels of CD3 and CD4. The antibody titer did not show a significant rise after receiving diphtheria and tetanus vaccines. Whole-exome sequencing was performed, and a novel homozygous c.248del, p.Pro83Leufs ∗3 variant was reported in the STK4 gene. The presence of this variant in parents was also confirmed with Sanger sequencing. CONCLUSION: STK4 deficiency is a rare cause of CID characterized by susceptibility to recurrent infections. Our case shows immune dysfunction manifested as a complex inflammatory syndrome, featuring an abdominal mass that mimics malignancy, expanding the recognized clinical spectrum of this condition.