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.