Two mutations in LDLR gene were found in two Chinese families with familial hypercholesterolemia.

Familial hypercholesterolemia (FH) (OMIM 143890) is an autosomal dominantly inherited disease mainly caused by mutations of the gene encoding the low density lipoprotein receptor (LDLR) and Apolipoprotein (Apo) B. First the common mutation R3500Q in ApoB gene was determined using PCR/RFLP method. Then the LDLR gene was screened for mutations using Touch-down PCR, SSCP and sequencing techniques. Furthermore, the secondary structure of the LDLR protein was predicted with ANTHEPROT5.0. The R3500Q mutation was absent in these two families. A heterozygous p.W483X mutation of LDLR gene was identified in family A which caused a premature stop codon, while a homozygous mutation p.A627T was found in family B. The predicted secondary structures of the mutant LDLR were altered. We identified two known mutations (p.W483X, p.A627T) of the LDLR gene in two Chinese FH families respectively.

[Mutation screening and functional analysis of low density lipoprotein receptor in a familial hypercholesterolemia family].

OBJECTIVE: To screen the mutations of the low density lipoprotein receptor (LDLR) gene in a familial hypercholesterolemia (FH) family, and analyze the LDL-uptaking function of LDLR on lymphocytes of patients. METHODS: Genomic DNA was extracted from four affected members in a Chinese FH family. The presence of apoB100 gene R3500Q mutation which results in familial defective apolipoprotein B100 (FDB) was excluded first. Fragments of the LDLR gene were amplified by touch-down polymerase chain reaction (Touch-down PCR) and analyzed by single-strand conformational polymorphism (SSCP). The suspect fragments of the LDLR gene were cloned and sequenced. Furthermore, the lymphocytes bounded with fluorescent-labeled LDL (DiI-LDL) were measured by fluorescence flow cytometry. RESULTS: A nonsense mutation was identified in exon 10 of LDLR gene. This mutation gave rise to a premature stop codon (W462X), resulting in the absence of most of the LDLR domains. It was detected in all the affected members of the FH family. The ratios of functional LDLR in lymphocytes from patients and normal controls were 63.7% and 77.3% respectively. As a result, the activity of the functional LDLR in patients was just 82.4% of that in the normal controls. CONCLUSION: It is possible that the W462X mutation of LDLR gene is the main cause for the disease in this family.