Table 1 Primary hypertriglyceridaemias and lipoprotein abnormalities

Type	Prevalence	Elevated lipoprotein	Fredrickson type	Appearance of serum on standing	Gene defect
Familial chylomicronaemia
Familial LPL deficiency	1/1000000	CM	I	Creamy supernatant, clear infranate	AR, LPL,115 ApoC-II116 or ApoAV deficiency,11 heterozygotes may have a mild abnormality
Familial ApoC-II or ApoAV deficiency	<1/1000000	CM	I	Creamy supernatant, clear infranate
Familial combined hyperlipidaemia	1–6%	LDL + VLDL	IIb	Turbid	AD/oligogenetic?*
Familial dysbetalipoproteinemia	1/10000114	IDL	III	Milky	ApoE-II homozygosity, AR, requires second abnormality for expression
Familial hyperlipidaemia	0.2–0.5%	VLDL	IIb	Turbid	Multiple, AD
Familial mixed hypertriglyceridaemia	<1/1000000	CM + VLDL	V	Creamy supernatant, turbid infranatant	Multiple, AR

While the genetic abnormalities associated with familial chylomicronaemia and familial dysbetalipoproteinaemia have been clarified, the primary triglyceridaemias are known to be modified by other genetic and environmental determinants. The Fredrickson classification is of little use in clinical practice, though it remains in common parlance.
*There is likely to be an overlap between the underlying metabolic defects associated with familial combined dyslipidaemia, the dyslipidaemia associated with insulin resistance and familial hypertriglyceridaemia.
AD, autosomal dominant; Apo, apolipoprotein; AR, autosomal recessive; CM, carboxymethylated; IDL, intermediate density lipoprotein; LDL, low density lipoprotein; VLDL, very low density lipoprotein.