Apolipoproteins

Apolipoproteins are the protein portion of lipoproteins that transports water-insoluble lipids in the blood. The following forms of apolipoproteins can be distinguished:

• Apolipoprotein A1 (apo A1; APOA1).
• Apolipoprotein A2 (apo A2; APOA2)
• Apolipoprotein B (apo B; APOB)
• Apolipoprotein B-100 (apo B-100; APOB-106)
• Apolipoprotein E (apo E; APOE)
• Apolipoprotein E isoforms

Different lipoproteins are occupied by apolipoproteins to varying degrees such as VLDL or chylomicrons with apo E

The process

The concentration of apolipoprotein can be determined by a laboratory diagnostic test from your blood serum. Material needed

• Blood serum

Indications

• Apo B-100, Apo A1: estimation of atherosclerosis risk, A-α-lipoproteinemia (eg, Tangier disease), A-β-lipoproteinemia.
• Apo CII: Apo CII deficiency (type I).
• Apo E: Apo E2 homozygosity (type III, Apo E increased), Apo E- deficiency (type III, Apo E decreased).

Normal value of apolipoproteins of adults.

Lipoprotein	Normal range
apoliprotein A1	90-170 mg/dl
Apolipoprotein A2	25-50 mg/dl
Apolipoprotein B	40-115 mg/dl
Apolipoprotein E	2.3-6.3 mg/dl

Diagnostics

Apo A1 and Apo B are missing

• A-α-lipoproteinemia (e.g., Tangier disease).
• A-β-lipoproteinemia

Apo CII deficiency

• Leads to type I hyperlipoproteinemia

Apo E increased

• Apo E-2 homozygosity:
  • Degradation of chylomicrons and VLDL is impaired.
  • Associated with type III hyperlipoproteinemia.
  • Intermediate products (IDL, reminants) are accumulated
  • Diagnosis confirmed by determining the distribution pattern of Apo E subtypes or PCR, if necessary.

Apolipoprotein E genotyping

Apo E	Allele combination	Frequency	Clinical effects
Genotype E2	E2/E2	approx. 0.5	Association with type III of Fredrickson’s hyperlipoproteinemia (familial dysbetalipoproteinemia; incidence approximately 1:2,000). Lowered risk for LDL cholesterol elevation. Heterozygous or homozygous ApoE2 carriers with combinations 2/3 and 2/2 (together about 5% of the population) have about 40.0% lower risk of dementia.
	E2/E3	ca 10.0 %	Decreased risk of LDL cholesterol elevation. Heterozygous or homozygous ApoE2 carriers with combinations 2/3 and 2/2 (approximately 11.0% of the population) have an approximately 40.0% lower risk of disease for dementia.
Genotype E3	E3/E3	approx. 60.0 %	Intermediate risk for LDL cholesterol elevation.
Genotype E4	E2/E4	approx. 2.5	Predisposed to the familial late form as well as the sporadic form of Alzheimer’s-type dementia; have an approximately 2.6 increased lifetime risk (European/Caucasian)
	E3/E4	approx. 24.0	Risk for LDL cholesterol elevation Predisposition to familial late-onset form as well as sporadic form of Alzheimer’s-type dementia; have approximately 3-fold increased lifetime risk compared to 3/3 carriers (approximately 60% of population)
	E4/E4	approx. 3 %	Risk for LDL cholesterol elevation Predisposition to familial late-onset form as well as sporadic form of Alzheimer’s-type dementia; have up to 10-fold increased risk of developing Alzheimer’s dementia.

Of those with AD, approximately 45% are heterozygous and 10-12% are homozygous carriers of the epsilon 4 alleleAn isolated determination of the apolipoprotein E genotype as a genetic risk factor is not recommended due to lack of diagnostic discriminatory power and predictive value in the diagnostic setting.