Familial hypercholesterolemia and familial defective apolipoprotein B-100: comparison of the phenotypic expression In 116 cases.

Familial hypercholesterolemia (FH) is characterized by an increased level of LDL cholesterol, tendon xanthomas and an elevated risk of premature coronary artery disease (CAD). FH is caused by different mutations in the low density lipoprotein receptor (LDLR) gene or by a G to A mutation in exon 26 of the apolipoprotein B gene causing familial defective apolipoprotein B-100 (FDB). To compare the phenotypic expression of either defect, we studied 83 patients (76 heterozygous and 7 homozygous persons) with LDLR defects and 33 heterozygous FDB patients from Germany. We took into account other risk factors for CAD. In contrast to earlier studies, our patients where prospectively ascertained from the lipid clinic and tested for the G-A mutation. The average total cholesterol level in plasma was 413.7 mg/dl in LDLR patients and 321.8 mg/dl in FDB patients. Patients with LDLR defects had a significantly higher risk of myocardial infarction, coronary artery bypass graft, positive coronary angiography, atherosclerotic plaques in the carotid arteries and CAD (p<0.01) than patients with FDB. CAD was present in 33% and plaques in the carotid arteries in 82% of the patients with LDLR defects. No patient with FDB had severe CAD, while only 52% had plaques in the carotid arteries (p<0.05). Thus in our study, hypercholesterolemia and premature atherosclerosis were more common in LDLR patients than in FDB patients. We believe that the striking difference in CHD incidence is not sufficiently explained by the higher LDL levels in LDLR patients. A possible explanation may be that in LDLR patients, the metabolism of low density lipoproteins, intermediate density lipoproteins and very low density lipoproteins is disrupted, whereas in FDB patients there is only disruption in apo B-containing LDL.