Two novel mutations 685del 1 and D129G in the low-density lipoprotein receptor gene in a compound heterozygote Chinese family with familial hypercholesterolemia

DNA sequencing analysis was used to scan the genes in a Chinese family with clinically diagnosed autosomal genetic hypercholesterolemia. Two mutations were identified in exon 4 of the low-density lipoprotein receptor gene, which is the possible molecular mechanism of etiology of the family. The proband's extremely high level of serum cholesterol and the related manifestations suggested that he was a familial hypercholesterolemia homozygote and that his parents were in a relatively milder condition. DNA sequencing revealed that the proband had an abnormal pattern of exon 4 of the low-density lipoprotein receptor gene 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 (D129G) changed this codon from AspGAC to GlyGGC. The single-base deletion of A at 685 (685del 1) is a frameshift mutation. It changes the phase of triplets, so that all codons are misread after this site of mutation; consequently, the protein expressed by the gene must be abnormal in structure and function. DNA analysis of the other family members showed that the 2 mutations should be respectively located in different alleles of the proband. Both of the 2 mutations have not been reported previously.