Collecting And The Gene Analysis Of A Monogenic Hypercholesterolemia Family

Generally atherogenesis is considered a polygenic disease and numerous candidate genes are proposed. In addition to environmental factors such as hypertension, diabetes, cigarette smoking and obesity, gene mutations affecting any of the metabolic pathways involved in the development of atherosclerosis may contribute to the risk of CHD. Not all cardiovascular diseases are polygenic in nature, and among patients with CHD onset before the age of 55, about 5% of cases are attributable to monogenic origin. Premature onset of the hypercholesterolemia often prompts that the genetic factors play more important roles. There are four main types of monogenic hypercholesterolemia which are closely related to the CHD and result respectively from mutations in the low density lipoprotein receptor (LDLR) gene, the apolipoprotein B-100 gene (apoB), the recently identified proprotein convertase subtilisin/kexin type 9 gene (PCSK9) and autosomal recessive hypercholesterolemia (ARH). These four types of hypercholesterolemia have a similar clinical phenotype which is characterized by increased plasma level of total cholesterol and low density lipoprotein cholesterol, the formation of cutaneous and tendinous xanthomata, arcus corneae and premature coronary heart disease. Among the four types of hypercholesterolemia, the first three are genetically autosomal dominant form, and there were no report of homozygote with mutations of PCSK9 gene. Clinically identified FH usually result from defects in the LDLR gene. Deficiency of LDLR results in accelerated cholesterol synthesis in cells and delayed clearance of LDL from the blood circulation. Homozygous deficient patients with two abnormal LDLR genes, either identical or different mutantgenes, which are rarely report, typically exhibit life-threatening coronary atherosclerosis and subsequent myocardial infarction before age 30. In the present study we collected and characterized a clinically diagnosed autosomal genetic hypercholesterolemia family, and scanned the related gene of the family for the possible mutations which were the potential molecular basis of etiology of the family in which the proband was suspected to be homozygous patient. We precluded the FDB by examine the previously reported mutations R3500Q, R3500W and R3531C. And then we described two novel different mutations in the LDLR gene, which made the family a compound heterozygous family.PART I Collecting, characterizing of a monogenetic hypercholesterolemia familyThe purpose of the study was to collect and characterize a hereditary hypercholesterolemia family and estabilish a elementary method of collecting hereditary family. In our study, we collected the resources including DNA samples, and accompanying clinical and pedigree data of a monogenic hypercholesterolemia family and establish a repository consisting of genome DNA, and accompanying clinical and pedigree data of the family.Family resources revealed an extremely high level of the serum cholesterol of the proband and moderately elevated serum cholesterol level of the parents. The proband and the parents were presumed to be homozygote and heterozygote respectively. The pedigree data showed an autosomal dominant inheritance pattern in the family. And these data were the basis of gene analysis.PART II Two novel mutations 685del A and 386A>G in the LDL receptor gene induced a compound heterozygote family with familial hypercholesterolemiaWe employed the analysis of DNA sequencing to scan the related gene of a clinical diagnosed autosomal genetic hypercholesterolemia family in china andidentify two mutations in exon 4 of the low density lipoprotein receptor gene which are possibly the molecular mechanism of etiology of the family. The proband's extremely high cholesterolemia and manifestation suggested he was a clinically a homozygote of FH. And his parents were in a relatively milder condition. DNA sequencing of the proband revealed that the abnormal pattern of exon 4 of LDLR gene was due to a heterozygosity (A/G) at nucleotide 386 and a heterozygous single base deletion (A) at 685. Nucleotide 386 is the second base of codon 129, and A-*G mutation change this condon from AspoAC to GlyoGC (D129G). The single base deletion of A at 685 (685del A) is a frameshift mutation. It changes the phase of triplets, so that all codons are misread after this site of mutation, and the protein the gene expresses must be abnormal in the structure and function. The DNA analysis of the other family members showed that the two mutations were paternal origin (685del A) and maternal origin (386A>G) respectively and should be located in different alleles of the proband. Both of the two mutations have not been reported previously.