Chediak–Higashi syndrome (CHS) is one of those Step 1 immunodeficiencies that shows up as a “classic vignette”: a kid with recurrent pyogenic infections plus partial albinism and neurologic problems. If you can explain why a lysosomal trafficking defect causes those exact findings—and recognize the peripheral smear clue—you’ll pick up easy points.
Where Chediak–Higashi Fits (Big Picture)
CHS is an autosomal recessive immunodeficiency caused by a defect in phagolysosome formation due to abnormal microtubule-dependent trafficking.
High-yield identity:
- AR
- LYST mutation (lysosomal trafficking regulator)
- Defective lysosomal granule formation/trafficking
- Giant granules in granulocytes/platelets
- Recurrent pyogenic infections
- Partial albinism + peripheral neuropathy
- Accelerated phase (hemophagocytic lymphohistiocytosis–like)
Definition (What It Is)
Chediak–Higashi syndrome is a rare phagocyte (and NK cell) dysfunction in which impaired trafficking and fusion of lysosomes leads to:
- impaired killing of ingested organisms by neutrophils/macrophages
- impaired cytotoxic granule exocytosis in NK cells/CTLs
- abnormal melanosome trafficking → hypopigmentation
- abnormal platelet dense granules → bleeding tendency
Pathophysiology (Why It Happens)
The Core Molecular Defect
- Mutation in LYST → defective regulation of lysosomal trafficking along microtubules
- Result: failure of proper phagosome–lysosome fusion and abnormal giant granules
What That Breaks (Step 1-Style)
1) Phagocytes can ingest but can’t kill well
- Phagocytosis occurs
- But the normal “phagolysosome killing compartment” is dysfunctional → recurrent bacterial infections, especially Staph aureus and Strep pyogenes
2) NK cells (and CTLs) have impaired degranulation
- Cytotoxic granules are abnormal → decreased NK cell function
- This contributes to infections and to the risk of an accelerated phase
3) Melanocytes don’t distribute melanin normally
- Abnormal melanosome trafficking → oculocutaneous albinism (often partial)
4) Platelet granules are abnormal
- Platelet dense bodies can be affected → easy bruising, mucosal bleeding
Clinical Presentation (How It Shows Up)
Classic Triad (Memorize This)
- Recurrent pyogenic infections (skin, respiratory)
- Partial albinism (light skin/hair, silvery hair)
- Peripheral neuropathy (neurologic dysfunction can be progressive)
Common Vignette Details
- Child with recurrent Staph/Strep infections
- Silvery hair, nystagmus/photophobia (from albinism)
- Easy bruising or prolonged bleeding
- Neutropenia may be present
Accelerated Phase (Very High Yield)
Many patients develop an “accelerated phase” resembling HLH (hemophagocytic lymphohistiocytosis), often triggered by EBV:
- fever, hepatosplenomegaly, lymphadenopathy
- pancytopenia
- hepatitis, coagulopathy
- can be life-threatening
USMLE hook: CHS can progress to a severe inflammatory/hemophagocytic syndrome—think EBV-associated HLH-like picture.
Diagnosis (How You Confirm It)
Peripheral Smear / Bone Marrow Clue
The board-style hallmark is:
- Giant granules in granulocytes (and other cells)
These represent fused/abnormally large lysosomal granules.
Other Supportive Findings
- Decreased NK cell activity
- Variable neutropenia
- Genetic testing: LYST mutation
Step 1 Differential: “Giant granules” vs other immunodeficiencies
| Disorder | Key Defect | Signature Clue | Typical Infections/Findings |
|---|---|---|---|
| Chediak–Higashi | AR, LYST, microtubule trafficking → poor phagolysosome fusion | Giant granules in granulocytes/platelets | Pyogenic infections + partial albinism, neuropathy, HLH-like accelerated phase |
| CGD | NADPH oxidase defect → ↓ ROS | Abnormal dihydrorhodamine test | Catalase+ (S. aureus, Serratia, Burkholderia, Nocardia, Aspergillus) |
| LAD-1 | CD18 integrin defect → impaired adhesion | No pus, delayed umbilical separation | No neutrophil extravasation, leukocytosis |
| MPO deficiency | impaired HOCl | Often asymptomatic | Sometimes Candida, but usually mild |
Treatment (What You Do)
Definitive / Disease-Modifying
- Hematopoietic stem cell transplant (HSCT) can correct the immune cell defect and reduce severe infections/accelerated phase risk.
Infection Management
- Aggressive treatment of bacterial infections
- Prophylactic antibiotics may be used depending on severity
- Supportive care for bleeding issues
Accelerated Phase
Managed similarly to HLH in specialized settings (immunochemotherapy protocols + treating triggers like EBV), with HSCT as the definitive long-term strategy.
High-Yield Associations & “Buzzwords”
Must-Recognize Vignette Triggers
- “Partial albinism” + recurrent pyogenic infections → think CHS
- “Giant granules in neutrophils” → CHS until proven otherwise
- Neurologic deficits (peripheral neuropathy, ataxia) alongside immunodeficiency → strongly supports CHS
- EBV-triggered accelerated phase → HLH-like picture
Organisms
- Classically Staphylococcus aureus and Streptococcus pyogenes
First Aid Cross-References (What to Link in Your Head)
In First Aid for the USMLE Step 1 (Immunology → immunodeficiencies), CHS is grouped with disorders of phagocyte function.
Cross-reference concepts to review right next to CHS:
- Phagocyte disorders: CGD, LAD, MPO deficiency
- NK cell function: connections to viral susceptibility and HLH concepts
- Albinism associations: distinguish CHS (immune + neuro + infections) from isolated oculocutaneous albinism (pigment-only)
(Edition page numbers vary; look under “Immunodeficiencies—Phagocyte Dysfunction” and the CHS entry with LYST and giant granules.)
Rapid Review (Exam-Day Checklist)
- Inheritance: Autosomal recessive
- Gene/Protein: LYST (lysosomal trafficking regulator)
- Defect: abnormal microtubule-dependent lysosomal trafficking → impaired phagolysosome formation and giant granules
- Key findings: recurrent pyogenic infections, partial albinism, peripheral neuropathy, bleeding tendency
- Smear: giant granules in granulocytes
- Complication: accelerated phase (HLH-like, often EBV-associated)
- Definitive tx: HSCT