Familial dyslipidemias are one of those Step “name → pattern → complication” topics that feel impossible until you have a sticky way to recall which lipoprotein is high and what it causes. Here’s a quick, shareable mnemonic set that lets you map Type I–V in seconds—plus the highest-yield one-liners USMLE loves.
The 10-second framework: “C-HYLO makes you FAT”
Think of the Fredrickson types as a “lipoprotein ladder”:
- C = Chylomicrons
- H = HDL (not a Fredrickson “type,” but shows up in questions)
- Y = VLDL (sounds like “why,” as in “why is TG high?”)
- L = LDL
- O = (ID)L remnant particles
Now pair that with the most testable idea:
Chylomicrons + VLDL = Triglycerides (TG) problems (pancreatitis)
LDL / IDL = Cholesterol problems (atherosclerosis, xanthomas)
The core mnemonic: “1 = ‘I’ can’t clear cream; 2 = ‘II’ much LDL; 3 = ‘III’ = IDL; 4 = ‘IV’ = VLDL; 5 = ‘V’ = VLDL + chylos”
Visual mnemonic device (memorize the pattern)
Picture a blood sample tube after spinning:
- Chylomicrons float → creamy top layer
- VLDL/LDL/IDL stay in plasma → turbid/opaque serum
If you see a “creamy supernatant,” think chylomicrons (Type I or V).
If you see “turbid serum,” think VLDL (Type IV or V).
High-yield table: Fredrickson dyslipidemias at a glance
| Type | What’s ↑ | Typical lipid pattern | Classic cause (buzzword) | High-yield clues | Big complications |
|---|---|---|---|---|---|
| I | Chylomicrons | ↑ TG (massive) | LPL deficiency or ApoC-II deficiency | Child with pancreatitis, eruptive xanthomas, lipemia retinalis; no premature atherosclerosis | Pancreatitis |
| IIa | LDL | ↑ Cholesterol | LDL receptor defect (familial hypercholesterolemia) or ApoB-100 defect | Tendon xanthomas, premature CAD; often normal TG | Early atherosclerosis |
| IIb | LDL + VLDL | ↑ Cholesterol + ↑ TG | “Combined hyperlipidemia” (overproduction of ApoB/VLDL) | Very common; premature CAD | Early atherosclerosis |
| III | IDL (remnants) | ↑ Cholesterol + ↑ TG | ApoE defect (classically ApoE2/E2) → impaired remnant clearance | Palmar xanthomas, tuberous xanthomas; “broad-beta” band on electrophoresis | Atherosclerosis (peripheral + coronary) |
| IV | VLDL | ↑ TG | Increased VLDL production; often assoc w/ obesity, DM, EtOH | Hypertriglyceridemia, pancreatitis risk rises as TG climbs | Pancreatitis (if severe) |
| V | Chylomicrons + VLDL | ↑↑ TG | Mixed (often LPL pathway + VLDL overproduction) | Looks like Type I plus VLDL; adult w/ pancreatitis | Pancreatitis |
One-liner explanations (perfect for rapid review)
- Type I: “Can’t hydrolyze TG in chylomicrons” → LPL or ApoC-II issue → pancreatitis, eruptive xanthomas, no early CAD.
- Type IIa: “Can’t clear LDL” → LDL receptor/ApoB problem → very high cholesterol, tendon xanthomas, early MI.
- Type IIb: “Too much LDL + VLDL” → combined hyperlipidemia → chol + TG high, early CAD.
- Type III: “Can’t clear remnants (IDL)” → ApoE defect → palmar xanthomas, atherosclerosis.
- Type IV: “Overproducing VLDL” (often metabolic syndrome) → TG high, pancreatitis if severe.
- Type V: “Type I + Type IV together” → chylomicrons + VLDL, very high TG, pancreatitis.
The “Apo + enzyme” mini-map (USMLE favorites)
Lipoprotein lipase (LPL)
- Location: endothelium (adipose + muscle capillaries)
- Function: hydrolyzes TG in chylomicrons and VLDL
- Activated by: ApoC-II
- Insulin upregulates LPL activity (high-yield in diabetes questions)
Defect in LPL or ApoC-II → Type I (chylomicronemia).
ApoE (remnant uptake)
- Function: hepatic uptake of chylomicron remnants and IDL
- Defect (ApoE2) → impaired remnant clearance → Type III
ApoB-100 / LDL receptor
- ApoB-100: ligand on LDL for LDL receptor binding
- LDL receptor defect or ApoB-100 defect → Type IIa
Rapid “if-then” test-taking rules
- If TG are extremely high (especially mg/dL) + abdominal pain → pancreatitis → think Type I or V.
- If tendon xanthomas + very high LDL → Type IIa.
- If palmar crease xanthomas → Type III until proven otherwise.
- If dyslipidemia + obesity/DM/EtOH with high TG → Type IV (or IIb depending on LDL).
Micro-mnemonic recap (share this)
“1 = Cream only (Chylos)”
“2 = LDL (bad cholesterol) ± VLDL”
“3 = IDL remnants (ApoE)”
“4 = VLDL (TG)”
“5 = VLDL + Cream (TG bomb)”