Chediak-Higashi Syndrome (CHS) is a rare genetic disorder that results in repeated bacterial infections and immunodeficiency, which could be severe and life-threatening. This disorder is caused by defective lysosomal trafficking and impairs the immune system, making patients highly vulnerable to infections. Early prevention and treatment are key to controlling these infections and reducing morbidity. This article explores why these infections occur and how they can be managed in patients with CHS.

What is Chediak-Higashi Syndrome?

Chediak-Higashi Syndrome (CHS) is an autosomal recessive genetic disorder caused by a mutation in the lysosomal trafficking regulator (LYST) gene, a highly conserved gene coding for the lysosomal trafficking regulator adaptor protein, which plays key roles in intracellular membrane trafficking into the lysosome and other lysosome-related organelles, as well as the storage and secretory functions of lysosomal granules.¹

The lysosome is an organelle found within cells that contains a diverse range of hydrolytic enzymes capable of breaking down macromolecules, cell debris, and other waste materials that the cell no longer needs. The lysosome is also known as the ‘scavenger’ of the cell due to its role in degrading dead pathogens, making it a crucial organelle in immune cells.²

In CHS, the absence of functional LYST protein results in abnormally enlarged lysosomes in immune cells, and CHS is often characterised by immunodeficiency and partial oculocutaneous albinism.³

It has been discovered that childhood-onset CHS is more severe, due to the production of non-functional LYST protein and a high risk of developing haemophagocytic lymphohistiocytosis (HLH), a fatal phase of CHS that results in hyperinflammation and organ failure.⁴ On the other hand, attenuated CHS is often seen in adolescent- and adult-onset cases, as this form is caused by a missense mutation that allows for some retained function of the LYST protein. While attenuated CHS involves milder immune issues, it is more commonly associated with progressive neurological disorders such as parkinsonism and ataxia.^5,6

Pathogenesis of Recurrent Infections in CHS

Patients suffering from CHS are extremely susceptible to recurrent bacterial infections due to defects in lysosomal trafficking. This section explores the fundamental cellular pathophysiology caused by mutations in the LYST gene, which affect an array of immune cells and their mechanisms.

Defect in Phagocytosis

A major immunological mechanism affected by the LYST mutation is phagocytosis, the process of engulfing and degrading extracellular pathogens. Immune cells that are able to carry out phagocytosis are called ‘phagocytes’, and the two main cell types that phagocytose are macrophages and neutrophils. In normal circumstances, a phagocyte recognises extracellular pathogens attached to its cell membrane and ingests them. The ingested pathogen is then trapped in a vesicle called the phagosome. The phagosome fuses with the lysosome, and the pathogen is killed by reactive oxygen species (ROS) and nitric oxide (NO) from lytic granules, after which it is degraded by hydrolytic enzymes released from the lysosome.⁷

However, due to the LYST protein’s role in regulating and controlling the size and amount of lysosomes in cells, having a mutation in the LYST gene means lysosomes fail to divide normally and break down into smaller vesicles, causing them to become abnormally large in CHS.⁸ As a result, these oversized lysosomes are unable to move around the cell as efficiently and are not able to travel quickly to the phagosome and fuse with it during phagocytosis. This also implies that lysosomes in CHS are incapable of releasing their hydrolytic enzymes efficiently or in the right amount.

Consequently, despite phagocytes still being able to engulf and ingest bacteria, the impaired chemotaxis (the movement towards infection signals) caused by poor fusion of giant lysosomes to phagosomes, as well as the delayed release of enzymes from lysosomes, results in ineffective bacterial killing and degradation. Bacteria are more likely to survive inside immune cells, and this leads to recurrent and severe bacterial infections.

Defect in Dendritic Cell Function

Besides affecting the phagocytosis pathway, the mutation in the LYST gene in CHS also impacts dendritic cells. Dendritic cells are specialised antigen-presenting cells (APCs) that play a pivotal role in initiating and regulating the adaptive immune response, and are often known as the bridge between innate and adaptive immune responses. A defect in dendritic cell function can have a great impact on the activation of helper (CD4⁺) T cells, cytotoxic (CD8⁺) T cells, as well as B cells, which are lymphocytes that mount a targeted defence against pathogens in an immune response.

Immature dendritic cells capture antigens from the peripheral tissue and load them onto their MHC-II compartments, becoming mature and activated dendritic cells. These mature dendritic cells migrate to the lymph node and present their antigens to CD4+ naive helper T cells, which are then activated and participate in the activation of other immune cell types, such as the killing mechanism of CD8+ cytotoxic T cells and production of antibodies by B cells. Activated CD4+ helper T cells also specialise into subsets, two of which play important roles in defence against bacterial infections: Type 1 helper cells (Th1) produce cytokines such as interferon gamma (IFN-γ), which activates macrophages to carry out phagocytosis, and Type 17 helper cells (Th17) release cytokines like interleukin-17 (IL-17), which is responsible for recruiting and activating neutrophils to infection and inflammation sites.⁹

In CHS, the MHC class II compartments exhibit a severe delay in maturation, as well as the processing and presentation of peptides on the dendritic cell surface. This means that there are much fewer peptide-MHC II complexes displayed on the dendritic cell surface, resulting in poorer naive T cell priming. As a result, LYST-mutated dendritic cells are much less efficient in priming and activating naive helper T cells. A reduced level of activated helper T cells leads to a significant reduction in cytotoxic T cell killing mechanisms, resulting in pathogens not being killed as effectively. Moreover, defective dendritic cells fail to efficiently drive CD4+ helper T cells into strong Th1 or Th17 responses. Without strong Th1 signals, macrophages do not receive enough IFN-γ stimulation for phagocytosis activation, whereas without strong Th17 signals, fewer neutrophils are recruited to infection sites to clear pathogens, leaving them free to multiply and spread. Th1 and Th17 are also crucial for B cell antibody production, since cytokine signals are required for their activation, resulting in weaker antibody-mediated immunity and making bacterial infections harder to control.¹⁰

Consequences

The defects in the immune system in CHS lead to severe clinical consequences. Impaired macrophage, neutrophil, and dendritic cell function can result in immunodeficiency, making patients highly vulnerable to recurrent and uncontrollable bacterial infections, such as skin and respiratory tract infections, which can progress to life-threatening sepsis. The loss of immune control can also trigger haemophagocytic lymphohistiocytosis (HLH), a fatal hyperinflammatory state referred to as the ‘accelerated phase’ of CHS, in which an uncontrolled cytokine storm (i.e. excessive cytokine release) leads to severe blood cell destruction, multi-organ failure, and potentially death.⁴

Management Strategies

Infection Control and Prevention

Since CHS involves recurrent bacterial infections, which can progress rapidly to severe complications, prompt infection control is vital, typically through the use of broad-spectrum antibiotics, medications effective against a wide range of bacteria that are used to treat severe and life-threatening bacterial infections. The use of broad-spectrum antibiotics, however, is often not preferred and is reserved only for cases where the specific causative bacteria have not yet been identified, as unnecessary and excessive use can contribute to antibiotic resistance. Once the causative bacteria are identified, treatment is switched to targeted therapy with specific antibiotics. To prevent and reduce the frequency of infections, most patients are also placed on prophylactic antibiotics and are advised to follow infection prevention practices, such as protecting the skin from injury, alongside regular monitoring for early signs of illness.¹¹ Some patients are also given vaccinations against common bacterial pathogens to provide additional protection, although live vaccines are generally avoided in the setting of immunodeficiency.

Definitive Treatment

Haematopoietic stem cell transplantation (HSCT) remains the only definitive treatment currently available for CHS. HSCT aims to eliminate the underlying disease and restore the function of the haematopoietic and immune systems by replacing the defective immune system with donor stem cells capable of producing fully functional immune cells. If performed early after diagnosis and before the onset of severe infections or the accelerated phase, HSCT can dramatically improve survival and long-term outcomes.^12,13 However, HSCT is a complex procedure, and several factors make it challenging in the treatment of CHS.

Firstly, a suitable donor must be found. Ideally, this would be a matched related or identical twin donor; however, most patients rely on mismatched related donors, such as haplo-identical donors (parent, child, or sibling), which could induce complications. Secondly, the transplantation presents a risk of graft-versus-host disease (GVHD), where the donor immune cells recognise the transplanted tissues as foreign and attack them, which could lead to severe complications. Lastly, patients with CHS often have existing infections or organ damage, and require intensive supportive care before, during, and after transplantation, including chemo-radiotherapy, long-term immunosuppressive drugs, antibiotics, and antivirals. Despite these challenges, HSCT remains the most successful option and offers the best chance of preventing both recurrent bacterial infection and progression to the accelerated phase, making it the most definitive management for CHS.

Summary

In conclusion, Chediak-Higashi Syndrome (CHS) is a rare genetic disorder that disrupts lysosomal trafficking and weakens multiple key components of the immune system. Defects in phagocytes, dendritic cells, and lymphocyte function leave patients highly susceptible to recurrent bacterial infections that may progress to sepsis and trigger haemophagocytic lymphohistiocytosis (HLH), the accelerated and fatal phase of CHS. Effective management relies on rapid infection control, prophylactic measures, and careful monitoring, but the only curative option remains early haematopoietic stem cell transplantation (HSCT), which restores immune function and significantly improves long-term outcomes.