Diagnosis: Zellweger Syndrome (Cerebrohepatorenal Syndrome)

Clinching the Diagnosis - Feature by Feature

The Key Biochemical Clue

• In Refsum disease: only phytanic acid is elevated (single enzyme defect - PhyH deficiency)
• In X-linked adrenoleukodystrophy: only VLCFA are elevated (ABCD1 transporter defect - alpha-oxidation remains intact)
• In Zellweger syndrome: BOTH are elevated - because the entire peroxisome is absent/non-functional, ALL peroxisomal functions fail simultaneously

Pathophysiology

• Beta-oxidation of VLCFA → VLCFA accumulate
• Alpha-oxidation of phytanic acid → phytanic acid accumulates
• Plasmalogen synthesis → ether phospholipid deficiency in myelin

Classic Clinical Features (from Adams and Victor's Neurology)

• Neonatal/early infantile onset
• Profound hypotonia ("floppy infant")
• Dysmorphic craniofacial features: high forehead, shallow orbits, hypertelorism, abnormal ear helices
• Hepatomegaly and hepatic dysfunction
• Multifocal seizures
• Poor visual fixation, cataracts, abnormal retinal pigmentation, optic atrophy
• Stippled calcifications of patellae and greater trochanters (highly characteristic on X-ray)
• Cortical renal cysts, thymic agenesis on autopsy
• Usually fatal within months to the first year of life; no effective treatment

Why NOT Down Syndrome?

• Down syndrome does NOT cause elevated VLCFA or phytanic acid
• The metabolic profile (peroxisomal markers) conclusively points to Zellweger syndrome

Gaucher's Disease - Notes

1. What is it? (Basic Concept)

• A lysosomal storage disorder (LSD) - the most common LSD worldwide
• The body cannot break down a fatty substance called glucocerebroside (glucosylceramide)
• It piles up inside macrophages (immune cells) in the liver, spleen, bone marrow, and brain
• Inheritance: Autosomal recessive (need 2 faulty gene copies)

2. The Enzyme Defect

• Gene involved: GBA1 on chromosome 1q21
• More than 600 mutations known
• Key mutations: N370S (most common in Ashkenazi Jews, only in Type 1), L444P (associated with Type 3)

3. The Pathology - "Gaucher Cells"

• Macrophages stuffed with glucocerebroside become enlarged
• They look like crumpled/wrinkled tissue paper under microscope
• Called Gaucher cells - the hallmark of the disease
• These cells infiltrate: liver, spleen, bone marrow

4. Types of Gaucher's Disease

Type 1 is the most common - especially in Ashkenazi Jews (carrier frequency ~1 in 16!)

5. Clinical Features (Signs & Symptoms)

ALL Types:

• Massive splenomegaly (spleen bigger than liver - characteristic)
• Hepatomegaly
• Bone pain / pathological fractures / avascular necrosis
• Erlenmeyer flask deformity on X-ray (widening of the lower femur - classic finding)
• Easy bruising (due to thrombocytopenia)
• Chronic fatigue
• Anemia

Type 2 only:

• Rapid neurodegeneration
• Laryngospasm, strabismus, seizures
• Failure to thrive
• Fatal in first 2 years

Type 3 only:

• Abnormal horizontal eye movements
• Myoclonic epilepsy
• Slower neurodegeneration + visceral + bone disease

Important Association:

• GBA1 mutations = biggest genetic risk factor for Parkinson's disease (5-10x increased risk)

6. Lab Findings

7. Diagnosis

1. Screen: Lyso-Gb1 biomarker (blood/dried blood spot)
2. Confirm: Glucocerebrosidase enzyme activity assay in leukocytes or fibroblasts
3. Molecular: GBA1 gene sequencing (required for full diagnosis, as pseudogene nearby complicates analysis)
4. Bone marrow biopsy shows Gaucher cells but NOT needed for diagnosis
5. Prenatal diagnosis possible via chorionic villus sampling or amniocentesis

8. Treatment

Option 1 - Enzyme Replacement Therapy (ERT)

• Give recombinant glucocerebrosidase IV every other week (15-60 IU/kg)
• Reverses anemia, thrombocytopenia, organomegaly in 12-36 months
• Does NOT cross blood-brain barrier - cannot treat neurologic forms
• Very expensive; must be continued lifelong

Option 2 - Substrate Reduction Therapy (SRT)

• Eliglustat (oral) - inhibits glucosylceramide synthase - reduces how much glucocerebroside is made
• Improves spleen/liver size, hemoglobin, platelet counts
• Check CYP2D6 status before prescribing (affects dosing and eligibility)
• Oral alternative to ERT in adults

Asymptomatic or mildly symptomatic patients do not always need treatment

9. Quick Memory Trick

"GAUCHEr = GlUCoCErebrosidase is missing → GlUCoCErebroside piles up → BIG spleen, BIG liver, bad BONES"

10. Comparison with Similar Diseases (Differentiation)

Lipid Storage Disorders (Sphingolipidoses) - Simple Notes

1. The Big Picture - What Are These Disorders?

One enzyme (scissor) is missing → the lipid it should cut piles up → cells get clogged → organs fail

• All are autosomal recessive (both copies of the gene must be faulty) - EXCEPT Fabry disease (X-linked)
• Most cause neurodegeneration because the brain is rich in sphingolipids
• The rate of lipid synthesis is NORMAL - only the breakdown is broken

2. The Master Diagram

3. Each Disease - Simple One-Page Summary

🔴 TAY-SACHS DISEASE

• Missing enzyme: Hexosaminidase A (alpha subunit)
• Stuff that piles up: GM2 ganglioside
• Where: Brain (no visceral involvement)
• Key features:
  • Rapid progressive neurodegeneration
  • Cherry-red spot on macula (retina)
  • Exaggerated startle response (loud sound → big jerk)
  • Blindness, seizures, muscle weakness
  • Death by age 2-4 years
• Population: Ashkenazi Jews, French Canadians, Louisiana Cajuns
• Memory tip: "TAY-Sachs = Two Alpha" → Hexosaminidase A (alpha subunit)

🔴 SANDHOFF DISEASE

• Missing enzyme: Hexosaminidase A AND B (both subunits)
• Stuff that piles up: GM2 ganglioside + globosides
• Same neurologic symptoms as Tay-Sachs BUT also has visceral (liver/spleen) involvement
• Memory tip: "SandHOFF = BOTH subunits OFF"

🟠 GAUCHER DISEASE (Most common LSD)

• Missing enzyme: Glucocerebrosidase (beta-glucosidase)
• Stuff that piles up: Glucocerebroside (in macrophages)
• Key features:
  • Massive splenomegaly > hepatomegaly
  • Bone pain, Erlenmeyer flask deformity on X-ray
  • Gaucher cells = macrophages with "crumpled tissue paper" cytoplasm
  • 3 types (Type 1 = no brain; Type 2 = severe brain; Type 3 = mild brain)
• Treatment: Enzyme replacement therapy (ERT) available
• Population: Ashkenazi Jews

🟠 NIEMANN-PICK DISEASE (Types A & B)

• Missing enzyme: Sphingomyelinase
• Stuff that piles up: Sphingomyelin (in macrophages/foam cells)
• Key features:
  • Hepatosplenomegaly
  • Cherry-red macula (in Type A)
  • Neurodegenerative course (Type A = severe brain involvement; Type B = no brain)
  • Foam cells in bone marrow
• Note: Niemann-Pick Type C is a different defect (cholesterol transport protein NPC1) - cholesterol accumulates

🟡 FABRY DISEASE (Only X-linked!)

• Missing enzyme: Alpha-galactosidase A
• Stuff that piles up: Globosides (ceramide trihexoside)
• Key features:
  • Red-purple skin rash (angiokeratomas) - especially around belly button/groin
  • Burning pain in hands and feet (acroparesthesias)
  • Kidney failure + Heart failure (later)
  • Corneal opacities
• Inheritance: X-linked - males severely affected; females can be carriers with mild symptoms
• Treatment: ERT available
• Memory tip: "FABRy = FABulous skin rash, no cherry spot"

🟡 GM1 GANGLIOSIDOSIS

• Missing enzyme: Beta-galactosidase-1
• Stuff that piles up: GM1 gangliosides + keratan sulfate
• Key features:
  • Neurologic deterioration
  • Hepatosplenomegaly
  • Skeletal deformities (looks like Hurler syndrome = gargoylism)
  • Cherry-red macula (infantile form)

🟢 METACHROMATIC LEUKODYSTROPHY (MLD)

• Missing enzyme: Arylsulfatase A (or saposin B activator protein)
• Stuff that piles up: Sulfatides (sulfated galactocerebroside)
• Key features:
  • Progressive demyelination (white matter destruction)
  • Cognitive deterioration → dementia
  • Progressive paralysis
  • Nerves stain yellow-brown with cresyl violet (metachromatic = changes color when stained)
• Memory tip: "MLD = Myelin Loss Disease"

🟢 KRABBE DISEASE (Globoid Cell Leukodystrophy)

• Missing enzyme: Beta-galactocerebrosidase
• Stuff that piles up: Galactocerebrosides (in macrophages → globoid cells)
• Key features:
  • Mental and motor deterioration
  • Blindness and deafness
  • Near-total loss of myelin
  • Globoid bodies = glycolipid-laden macrophages in brain white matter (hallmark)

🔵 FARBER DISEASE

• Missing enzyme: Ceramidase
• Stuff that piles up: Ceramide
• Key features:
  • Painful, progressive joint deformity
  • Subcutaneous nodules (lumps under skin) containing lipid-laden cells
  • Hoarse cry (laryngeal involvement)
  • Tissue granulomas
  • Cherry-red macula

4. The Master Comparison Table

5. Common Themes to Remember

The macula (center of retina) has only one cell layer - you see the underlying red choroidal vessels. Surrounding retina is white because ganglion cells are engorged with lipid. Seen in: Tay-Sachs, Sandhoff, Niemann-Pick A, GM1, Farber

6. Simple Memory Tricks