Mutation Analysis and Hypercholesterolemia: Studies in FH patients and in healthy middle-aged men with high, low, or increasing cholesterol levels during a six-year follow-up (the CRISS study).

Our aims were to characterize familial hypercholesterolemia (FH) in a Swedish FH population and to further elucidate the clinical expression and treatment response in relation to genotype. Secondly, we wanted to identify gene variants, which may have impact on cholesterol levels in apparently healthy subjects. In the search for sequence alterations in the large LDL receptor gene we introduced and refined a sensitive screening method, based on denaturing gradient gel electrophoresis (DGGE). In DNA from 25 FH patients (one homozygote), pathogenic mutations were demonstrated in 18 of the 26 FH alleles (69%) expected to be at hand. This result emphasizes the high sensitivity of the screening system. No single genetic defect predominates in Swedish FH patients. Neither were any large deletions within the LDL receptor gene, nor the apo B-3500 allele, encountered. Four patients with the substitution C122X and four W66G carriers showed about equally high S-Cholesterol levels. Although the treatment response was approximately 45% decrease in LDL-Cholesterol for both of the groups, there was a tendency that the dose-response differed between the two groups, which stimulates to further investigations. Some of the found mutations were also investigated in order to describe their pathogenic potential and genotype-phenotype relationship. Cell culture studies demonstrated that the substitutions C240F and I402T are deleterious for LDL receptor function. In contrast, E256K resulted in virtually normal function. To investigate whether increasing cholesterol concentrations during a six-year follow-up could be attributed to genetic variations, selected parts of the LDL receptor and apo B genes were investigated in: (I) men with high serum cholesterol levels at the entry (n=84); (II) men who showed an increase (n=182) and (III) men who had low cholesterol levels throughout the study (n=77). Pathogenic mutations were mainly encountered in group I. The apo B substitution R3500Q and a previously not described apo B substitution (R3480W) were detected. Seven different sequence alterations were found in the LDL receptor gene. The frequencies of StuI(+) and StuI(-) alleles in exon 8 of the LDL receptor gene differed significantly between the groups (pStuI(-) allele in group III (allele frequency 0.006) was markedly lower than observed in other populations