Mannose binding lectin deficiency: more than meets the eye.

This case report describes a 5-year-old boy who presented to the emergency department with clinical symptoms and chest X-ray findings suggestive of pneumonia. Further history revealed multiple other infections, and workup for immunodeficiency revealed a deficiency of mannose-binding lectin (MBL), a pattern recognition receptor involved in activation of the complement system. Innate immunodeficiency may be more common than currently appreciated, with mutations of MBL affecting up to 50% of individuals in some populations. While pneumonia is a common presentation in the Pediatric Emergency Department, clinical presentations of children with defects of innate immunity can be unpredictable. Children may initially appear well with sudden deterioration. These cases pose particular challenges to physicians, and the level of suspicion for innate defects must remain high. It is crucial to identify patients with such impairments to better manage and prevent future complications.