Background: Neurodevelopment is closely entwined with immune maturation and function during embryogenesis. While haematopoietic-derived microglia have recognized roles in a number of neurodevelopmental processes, the contribution of molecules classically involved in the immune system (including complement, toll-like receptors, and cytokines) are also emerging. To date, approximately 11% of genes known to cause primary immunodeficiency also confer varying degrees of neurological abnormalities. These can range from intellectual disability, cognitive and behavioural disorders, through to seizures, spasticity, and motor development delay. However, very rarely are sensory processing defects associated with aberrations of the immune system.Aims: To define the clinical presentation and immune phenotype of a novel syndrome encompassing immunodeficiency, neurodevelopmental abnormalities, and altered pain sensitivity in two siblings.Methods: Comprehensive retrospective review of the patient’s charts were performed, in accordance with local research ethics board approval.Results: We describe two teenage sisters who presented with recurrent sinopulmonary infections, lymphopenia affecting both B and T cells, developmental delay, learning and processing disorder, seizures, and reduced sensitivity to pain. Other features include bronchogenic cyst, microscopic hematuria, oral ulcers, papular urticaria, and keratosis pilaris.Conclusion: An underlying defect in genes known to cause primary immunodeficiency was not identified, suggesting the role of an as-yet undefined molecule at the crossroads of immunity, neurodevelopment, and sensory processing.Statement of novelty: We report on two patients, siblings, with a novel phenotype of combined immunodeficiency, neurodevelopmental delay, and reduced sensitivity to painful stimuli.