APOLIPOPROTEIN-E PHENOTYPES AND PLASMA-LIPIDS IN DIABETIC CHILDREN AND ADOLESCENTS

Apolipoprotein E (apoE) polymorphism is a genetic determinant of serum lipoprotein levels and coronary heart disease risk. ApoE appears in t hree major isoforms E2, E3 and E4, coded by corresponding alleles epsi lon2, epsilon3 and epsilon4. These give six different phenotypes. Pati ents with insulin dependent diabetes (IDDM) have been reported to have increased incidence of E2/2 homozygosity. We studied the frequencies of apoE phenotypes and their association with plasma lipids in 201 dia betic children, aged 2-17 years, and in 216 healthy controls with the same age range. Phenotyping was performed directly from plasma by iso- electric focusing and immunoblotting. Plasma total and high density li poprotein (HDL) cholesterol (C) and triglycerides were determined by r outine laboratory methods. Apolipoprotein Al (apoA1) and B (apoB) were measured by turbidometry. There were no differences in apoE phenotype or allele distributions between the diabetic and control subjects. Th e frequencies of epsilon2, epsilon3, and epsilon4 in the diabetic and control children were 0.08 versus 0.07, 0.73 versus 0.72 and 0.19 vers us 0.21. The difference in apoE2/2 frequencies (2.0 in diabetic and 0. 5% in normal children) was not statistically significant. In the diabe tic children, there was a distinct relation between apoE phenotype and plasma lipids; presence of apoE2 was associated with the lowest and t hat of apoE4 with the highest concentrations of total and low density lipoprotein (LDL) C, and apoB. Ratios of HDL-C/LDL-C and apoA1/apoB sh owed on opposite trend. The influence of apoE polymorphism on plasma l ipids was less clear in the controls. ApoE polymorphism did not relate to body mass index, glycohaemoglobin Alc or daily insulin dosage. As compared to controls, diabetic children had significantly lower concen trations of total and LDL-C and apoB as well as higher ratios of HDL-C /LDL-C and apoA1/apoB. In conclusion, there was no difference in distr ibution of apoE phenotypes or alleles between diabetic and non-diabeti c children. ApoE polymorphism proved to be an important genetic determ inant of plasma lipid levels in patients with IDDM.