Chediak-Higashi Syndrome Mnemonic: The CHEDIAK Acronym

The Chediak-Higashi syndrome mnemonic is CHEDIAK: Clumsy chemotaxis, Hypopigmentation, Enlarged granules, Defective degranulation, Infections, Axonal neuropathy and Killer (NK) cells impaired. All seven trace to one autosomal recessive defect: biallelic variants in LYST (lysosomal trafficking regulator) leave many cell types, from neutrophils to melanocytes and neurons, with giant, poorly working lysosomes and lysosome-related organelles. Giant granules on the peripheral smear are the pathognomonic clue.

The CHEDIAK mnemonic, letter by letter

Add two facts to CHEDIAK: a mild bleeding tendency (nosebleeds, gum bleeding, easy bruising) from absent or reduced platelet dense granules, usually with a normal platelet count; and the accelerated phase (HLH) as the most common cause of death.

PLAIN gives the clinical picture: Progressive neurodegeneration, Lymphohistiocytosis (HLH), partial Albinism, recurrent pyogenic Infections and peripheral Neuropathy. Use CHEDIAK for mechanism and PLAIN for the patient in the stem.

Picture it: a pale, silver-haired cheetah ("CHEE-diak"), cheeks full of giant granules, too slow to catch prey and later stumbling on numb feet.

Genetics: the LYST mutation and autosomal recessive inheritance

• Gene: LYST (also called CHS1) on chromosome 1q42.3 encodes the lysosomal-trafficking regulator, a large cytoplasmic protein with a BEACH ("Beige and Chediak-Higashi") domain. It is thought to regulate lysosome size, fission and fusion, but its exact role is unknown.
• Inheritance: autosomal recessive. Parents are usually healthy carriers; each sibling of an affected child has a 25% chance of being affected, 50% of being a carrier and 25% of being neither. Consanguinity raises the risk.
• Genotype and severity: loss-of-function variants (nonsense, frameshift, canonical splice site, exon deletions) are typically associated with classic childhood-onset disease, and missense variants or in-frame deletions with atypical adolescent- or adult-onset disease, with exceptions.
• How rare: fewer than 500 people have been reported; mildly affected adults are probably underrecognized.
• Classification: the 2024 International Union of Immunological Societies (IUIS) update lists it among familial HLH (FHL) syndromes with hypopigmentation, alongside Griscelli type 2 and Hermansky-Pudlak type 2; the Merck Manual describes it as a primary immunodeficiency involving phagocytic cell defects.

Pathophysiology: one trafficking defect, many organelles

LYST is thought to help lysosomes split apart (fission) after fusion events. Without it, lysosomes and lysosome-related organelles become oversized and dysfunctional; in neutrophils, the giant granules arise from abnormal fusion of primary (azurophilic) and secondary (specific) granules.

A trafficking disorder, not a classic storage disease. Nearly 70% of lysosomal storage diseases come from enzyme defects and the rest from defective activator or associated proteins; animal models instead place LYST in lysosome fission and trafficking, not degradation.

Why review books say "microtubule dysfunction." A 1976 neutrophil study proposed impaired microtubule function, and USMLE review resources still word the mechanism as microtubule dysfunction (defective microtubule polymerization) that impairs phagosome–lysosome fusion. A 1993 study found that lysosomes in the beige mouse model still interact normally with microtubule-based motors, and current references describe a LYST-regulated defect in lysosome size and trafficking. On the exam, treat "microtubule dysfunction in phagosome–lysosome fusion" and "lysosomal trafficking defect (LYST)" as the same disease.

Clinical features: classic vs atypical disease

Chediak-Higashi syndrome is a continuum, from severe childhood-onset ("classic") disease to milder adolescent- or adult-onset ("atypical") disease. Giant leukocyte granules occur across the whole spectrum.

• Skin, hair and eyes: silvery or metallic hair; pigment dilution can be subtle unless compared with relatives, and darker skin may show scattered hyper- and hypopigmented areas. Iris transillumination, reduced retinal pigment, nystagmus and photophobia; visual acuity ranges from normal to moderately reduced.
• Infections and mouth: skin and upper respiratory infections are most common, and viral and fungal infections also occur. Periodontitis can be the finding that leads to the diagnosis. Neutropenia may be present and can be cyclic.
• Neurologic decline: learning difficulties may appear in childhood. A sensory neuropathy typically starts in late adolescence or the early 20s and progresses to a sensorimotor neuropathy or diffuse motor neuronopathy. Cerebellar ataxia, optic neuropathy, spastic paraplegia, tremor, parkinsonism (sometimes levodopa-responsive) and late cognitive decline can follow.

The accelerated phase is HLH

The accelerated phase, once thought to be a lymphoma-like malignancy, is hemophagocytic lymphohistiocytosis: a hyperinflammatory state in which lymphocytes and histiocytes infiltrate the liver, spleen, bone marrow, lymph nodes and central nervous system.

• How often: HLH develops in most patients who have not had a stem cell transplant, at any age; the risk is highest, about 85%, in classic disease.
• Why: abnormal function of NK cells and cytotoxic T cells is believed to contribute. Epstein-Barr virus is suspected as a trigger, but the link has never been proven.
• What it looks like: fever, lymphadenopathy, hepatosplenomegaly, anemia, neutropenia and thrombocytopenia.
• Why it matters: HLH and its complications are the most common cause of death; severe infections are the other main cause in untreated children.

Diagnostic criteria. GeneReviews (2023) diagnoses HLH in Chediak-Higashi syndrome with the familial HLH criteria, which then meant HLH-2004: a molecular diagnosis or 5 of 8 findings, including low NK-cell activity. The Histiocyte Society's 2024 revision, built on children with familial HLH or Griscelli type 2 (Chediak-Higashi patients were not included), drops NK-cell activity, leaving a clinical pathway of 5 of these 7:

A molecular diagnosis or abnormal lymphocyte cytotoxicity tests in a patient with signs of HLH also establish the diagnosis. Untransplanted patients are screened at least yearly with abdominal ultrasound, blood counts, ferritin, triglycerides, fibrinogen and soluble IL-2 receptor.

Diagnosis: start with the smear

1. Peripheral blood smear: giant peroxidase-positive granules, mainly in neutrophils, also in monocytes and less often lymphocytes, are the most reliable diagnostic criterion. An automated count can miss them and they can be subtle in atypical disease, so a hematologist should review the slide.
2. Hair microscopy: pigment clumps in the hair shaft instead of evenly spread melanin; a quick screen.
3. Platelet electron microscopy: absent or reduced dense bodies.
4. Immune tests: NK cells normal or reduced in number, with reduced function; antibody production and complement normal.
5. Genetic testing: biallelic pathogenic LYST variants confirm the diagnosis; sequence analysis detects about 97% of known variants.
6. Test siblings early (targeted genetic testing or a smear), so transplant can happen before HLH.

Treatment: transplant early, control HLH first

• Hematopoietic stem cell transplantation (HSCT) is the only targeted, curative treatment for the hematologic and immunologic defects. Preparation often starts once the diagnosis is confirmed; outcomes are best before HLH develops. In one series of 35 children, 5-year survival after HSCT was 62%.
• HSCT does not protect the nervous system: neurologic disease still appears by early adulthood after a successful transplant.
• If HLH develops, it must be brought into remission before HSCT. The Histiocyte Society HLH-94 protocol remains the usual standard: etoposide plus dexamethasone, with cyclosporine A added in the continuation phase and intrathecal methotrexate for selected patients with central nervous system disease. HLH-2004, which moved cyclosporine to the start, was not shown to be better. Emapalumab, an interferon-gamma–neutralizing antibody, is FDA-approved for primary HLH that is refractory, recurrent or progressive, or when conventional therapy is not tolerated.
• Infections: prompt, aggressive antibiotics or antivirals, prophylactic antibiotics considered for recurrent infections, inactivated vaccines on schedule and regular dental care.
• Bleeding: IV desmopressin (DDAVP) 30 minutes before invasive procedures; platelet transfusion for serious trauma or extensive bleeding.
• Avoid: live vaccines and all NSAIDs, including aspirin and ibuprofen.
• Supportive care: sunscreen, UV-blocking sunglasses, low-vision services, rehabilitation, and a levodopa trial for parkinsonism.
• Prognosis: without treatment, median survival generally extends only through the first decade of life.

Chediak-Higashi vs look-alikes

Only Chediak-Higashi syndrome here has giant granules, so the smear separates it fastest. Go deeper with chronic granulomatous disease, Job syndrome and Wiskott-Aldrich syndrome.

Classic exam traps

• Giant granules are not Birbeck granules, the rod-shaped inclusions seen on electron microscopy in Langerhans cell histiocytosis.
• Giant granules in acute or chronic myeloid leukemia are the pseudo-Chediak-Higashi anomaly, not the syndrome.
• An abnormal DHR test points to CGD; a defective oxidative burst is not a feature of Chediak-Higashi syndrome.
• Bleeding with a normal platelet count reflects missing dense granules. Thrombocytopenia with small platelets suggests Wiskott-Aldrich syndrome; fever, splenomegaly and falling counts in a child with CHS suggest HLH.
• Inheritance is autosomal recessive, unlike Wiskott-Aldrich syndrome and most chronic granulomatous disease (X-linked).
• Absent albinism does not exclude the diagnosis: some people with atypical disease have none, and neurologic problems may dominate.
• Transplant fixes the blood, not the brain: after successful HSCT, a young adult can still develop neuropathy, ataxia or parkinsonism.

Worked examples

Vignette 1. A 2-year-old boy has had three staphylococcal skin abscesses, recurrent upper respiratory infections and frequent nosebleeds. He has light skin, silvery-gray hair, photophobia and horizontal nystagmus. His platelet count is normal. The smear shows neutrophils with giant cytoplasmic granules, and a dihydrorhodamine (DHR) test is normal. Which cellular process is defective?

Answer: Lysosomal trafficking, from biallelic LYST variants (Chediak-Higashi syndrome).

Reasoning: Partial albinism, pyogenic infections, bleeding with a normal count and giant granules make the diagnosis; a normal DHR test argues against CGD.

Vignette 2. A 7-month-old girl has silvery-gray hair, persistent fever, hepatosplenomegaly and pancytopenia. Ferritin is 9,000 µg/L, fasting triglycerides are high, fibrinogen is low and the marrow shows hemophagocytosis. Her neutrophils have no giant granules, and platelet dense bodies are normal on electron microscopy. What is the most likely diagnosis?

Answer: Griscelli syndrome type 2 (RAB27A), presenting with HLH.

Reasoning: Silvery hair plus HLH fits Griscelli type 2 and Chediak-Higashi syndrome, but absent giant granules and normal dense bodies exclude Chediak-Higashi; normal dense bodies also argue against Hermansky-Pudlak. Familial HLH would not explain the pigment change.

Vignette 3. A 26-year-old woman had an allogeneic stem cell transplant at age 8 for classic Chediak-Higashi syndrome. Her blood counts are normal and serious infections have stopped. Over 2 years she has developed bilateral foot drop, numb feet and absent ankle reflexes. Nerve conduction studies show low-amplitude sensory and motor responses in the legs with normal conduction velocities. What explains her new problem?

Answer: Progressive Chediak-Higashi neurodegeneration (a length-dependent axonal sensorimotor neuropathy), which transplant does not prevent.

Reasoning: HSCT corrects the blood and immune defects, not the nervous system. Low amplitudes with normal conduction velocities mean an axonal process. In a National Institutes of Health cohort, adults transplanted in childhood developed neuropathy while transplanted children had not, pointing to degeneration rather than conditioning drugs.

Key takeaways

• CHEDIAK: Clumsy chemotaxis, Hypopigmentation, Enlarged granules, Defective degranulation, Infections, Axonal neuropathy, Killer (NK) cells impaired; PLAIN sums up the clinical picture.
• Autosomal recessive LYST variants (1q42.3) cause giant lysosomes; giant peroxidase-positive granules on the smear are pathognomonic, and LYST testing confirms.
• The accelerated phase is HLH: about 85% in classic disease and the most common cause of death; treat with the HLH-94 approach, then transplant.
• Early HSCT cures the blood and immune defects, not the neurologic disease.
• No giant granules? Think Griscelli type 2 (silvery hair, HLH), Hermansky-Pudlak (albinism, bleeding, lung fibrosis) or, with an abnormal DHR test, CGD.

More immunodeficiency reviews are on the immunology topic hub.

Sources

• Chediak-Higashi Syndrome — GeneReviews, NCBI Bookshelf
• Chediak-Higashi Syndrome — StatPearls, NCBI Bookshelf
• Chédiak-Higashi Syndrome — Merck Manual Professional Edition
• Lehky TJ, et al. Peripheral nervous system manifestations of Chediak-Higashi disease. Muscle Nerve. 2017 (PubMed)
• Misra VP, et al. Peripheral neuropathy in the Chediak-Higashi syndrome. Acta Neuropathol. 1991 (PubMed)
• Oliver JM. Impaired microtubule function correctable by cyclic GMP and cholinergic agonists in the Chediak-Higashi syndrome. Am J Pathol. 1976 (PubMed)
• Perou CM, Kaplan J. Chediak-Higashi syndrome is not due to a defect in microtubule-based lysosomal mobility. J Cell Sci. 1993 (PubMed)
• Poli MC, et al. Human inborn errors of immunity: 2024 update on the classification from the IUIS Expert Committee. J Hum Immun. 2025 (PubMed)
• Familial Hemophagocytic Lymphohistiocytosis — GeneReviews, NCBI Bookshelf
• Henter JI, et al. Diagnostic guidelines for familial hemophagocytic lymphohistiocytosis revisited. Blood. 2024 (PubMed)
• Gamifant (emapalumab-lzsg) prescribing information — DailyMed, US National Library of Medicine
• Hermansky-Pudlak Syndrome — GeneReviews, NCBI Bookshelf
• Chronic Granulomatous Disease — GeneReviews, NCBI Bookshelf
• Leukocyte Adhesion Deficiency — StatPearls, NCBI Bookshelf
• STAT3 Hyper IgE Syndrome — GeneReviews, NCBI Bookshelf
• WAS-Related Disorders — GeneReviews, NCBI Bookshelf
• Lysosomal Storage Disease — StatPearls, NCBI Bookshelf
• Langerhans Cell Histiocytosis — StatPearls, NCBI Bookshelf