Clin Genet 1999: 55: 67–68 Printed in Ireland. All rights resered Letter to the Editor Genetic investigation of patients with hypercholesterolemia type IIa To the Editor: Hypercholesterolemia is one of the most frequent disorders in Hungary with a complex, mostly un- known genetic background. Several factors can influence cholesterol levels. Three important ge- netic factors are polymorphisms in the apolipo- protein (apo) E gene, mutations in the apoB and low density lipoprotein (LDL) receptor genes. In our study we investigated the apoE, apoB and LDL receptor genes in 210 (100 male, 110 female, age 12–65 (52.5  18.6) years) unrelated Hungar- ian hypercholesterolemic patients with hyperc- holesterolemia type IIa. Isotypings of apoE were carried out by DNA amplification and digestion with HhaI as proposed by Hixson (1). The receptor binding domain of apoB-100 was investigated by allele-specific and asymmetric polymerase chain re- action (PCR) as proposed by Schuster (2). Exon 4a of the LDL receptor gene was amplified by PCR with the oligonucleotide primers proposed by Hobbs (3). The single strand conformation polymorphism (SSCP) analysis of the exon 4a of the LDL receptor gene and the amplified apoB fragments was carried out in the PhastSystem™ automated electrophoresis system (Pharmacia LKB, Uppsala, Sweden). The samples were screened for familial hypercholesterolemia (FH)- Elverum and FH-Helsinki as proposed by Leren (4) and Aalto-Seta ¨la ¨ (5), respectively. Calculated allele frequencies of 6.4 for apoE 2 , 79.3 for apoE 3 , and 14.3% for apoE 4 were seen with no significant difference between the fre- quency of apoE genotypes in patients with hyper- cholesterolemia and in the general population in Hungary (6). The apoE genotype distribution was in Hardy – Weinberg equilibrium. The total choles- terol values did not vary significantly among the genotype groups. These findings suggest that apoE isoforms do not play an important role in hyperc- holesterolemia type IIa and do not influence sig- Fig. 1. A) DNA sequence analysis of exon 4a of LDL receptor genes from a normal subject and from an FH patient surrounding codon 92; B) DNA sequence analysis of exon 4a of LDL receptor genes from a normal subject and from an FH patient surrounding codon 96; C) SSCP analysis of exon 4a of the LDL receptor gene with PhastSystem™, using 12.5% homogenous polyacrylamide minigel and silver staining; D) SSCP analysis of the ligand-binding part of apoB-100 gene with PhastSystem™, using 12.5% homogenous polyacrylamide minigel and silver staining. The two band pattern represents the wild type, the four band pattern represents the R3500Q mutation. 67