INTRODUCTION
Heme oxygenase is an important enzyme in heme metabolism. It facilitates the conversion of heme to biliverdin, which is further converted to bilirubin. Other products of heme metabolism include free ferrous iron and carbon monoxide (CO). There are three isoforms of this enzyme. Heme oxygenase-1 is an inducible form and is expressed in the reticuloendothelial system in response to hypoxia and ischemia. Heme oxygenase-2 is constitutively expressed in the brain, testis, and vascular endothelium and maintains cellular heme levels. The biological function of heme oxygenase-3 is presently under investigation. Bilirubin protects cells from oxidative injury by scavenging reactive oxygen species (1). Carbon monoxide acts as a signaling molecule in vasodilation, anti-inflammatory reactions, and cellular defense against apoptosis and oxidative damage (2). HO releases free iron, which gets incorporated into ferritin to maintain cellular iron homeostasis.
Several studies have examined the role of Heme Oxygenase 1 (HO-1) in in vitro tests and animal models. However, based on available reports (3,4), only 9 human cases have been documented since its first description by Yachie et al. in 1999. The rarity of this condition may be attributed to the crucial role of HO-1 in fetal growth and development. Reported cases exhibit a wide range of age of onset, from infancy to 15 years. Despite this variation, many similarities have been observed in their clinical presentation and laboratory findings. Most notably, patients typically exhibit abnormally low or normal bilirubin levels despite active hemolysis. Other findings include asplenia, vasculitis, nephritis, and features of hemophagocytic lymphohistiocytosis (HLH) (3). We present a case of a 3-year-old boy with heme oxygenase 1 deficiency. We aim to focus on the literature review and widen the gaze of clinicians on this rare entity.