FH-Sydney 1 and 2: two novel frameshift mutations in exon 10 of the low-density lipoprotein receptor gene detected by heteroduplex formation

Case report-Rapid regression of xanthomas under lipoprotein apheresis in a boy with homozygous familial hypercholesterolemia

Xanthomas are visibly deforming cholesterol deposits that develop after long-term exposure to high serum low-density lipoprotein cholesterol concentrations. We present the case of a 10-year-old boy suffering from homozygous familial hypercholesterolemia with generalized atherosclerosis and large xanthomas. The case impressively demonstrates the potential of low-density lipoprotein cholesterol lowering to rapidly regress pathologic cutaneous manifestations of hypercholesterolemia.

An improved method on stimulated T-lymphocytes to functionally characterize novel and known LDLR mutations

The main causes of familial hypercholesterolemia (FH) are mutations in LDL receptor (LDLR) gene. Functional studies are necessary to demonstrate the LDLR function impairment caused by mutations and would be useful as a diagnostic tool if they allow discrimination between FH patients and controls. In order to identify the best method to detect LDLR activity, we compared continuous Epstein-Barr virus (EBV)-transformed B-lymphocytes and mitogen stimulated T-lymphocytes. In addition, we characterized both novel and known mutations in the LDLR gene. T-lymphocytes and EBV-transformed B-lymphocytes were obtained from peripheral blood of 24 FH patients and 24 control subjects. Functional assays were performed by incubation with fluorescent LDL followed by flow cytometry analysis. Residual LDLR activity was calculated normalizing fluorescence for the mean fluorescence of controls. With stimulated T-lymphocytes we obtained a better discrimination capacity between controls and FH patients compared with EBV-transformed B-lymphocytes as demonstrated by receiver operating characteristic (ROC) curve analysis (the areas under the curve are 1.000 and 0.984 respectively; P < 0.0001 both). The characterization of LDLR activity through T-lymphocytes is more simple and faster than the use of EBV-transformed B-lymphocytes and allows a complete discrimination between controls and FH patients. Therefore the evaluation of residual LDLR activity could be helpful not only for mutation characterization but also for diagnostic purposes.

Spectrum of LDL receptor gene mutations in heterozygous familial hypercholesterolemia

Familial hypercholesterolemia by usual definition reflects mutations of the LDL-receptor gene. Extensive molecular characterization of mutations ascertained mainly through homozygotes (the Dallas collection) has been presented by Hobbs et al. (Hum Mutat 1:445-446, 1992). This paper catalogues a spectrum of 134 mutations (27 novel mutations in 45 patients, 24 previously described mutations in 89 patients) ascertained through heterozygotes from the analysis of 791 patients with definite, probable, or possible FH, mainly from the UK, using high-throughput modifications of the single-strand conformation polymorphism technique. From a composite database of LDL receptor gene mutations complied from these two sets and from the literature, deductions are made about ascertainment bias, mutation rates, and molecular heterogeneity. Calculations suggest that there may be a large number of rare amino acid variants in the general population not causing classic FH. Approaches to, and feasibility of, molecular diagnostics are considered.

Identification of two novel LDL receptor gene defects in French-Canadian pediatric population: mutational analysis and biochemical studies

Familial hypercholesterolemia (FH) is at least twofold more prevalent in French Canadians from Québec than in most Western populations. Although our recent data confirmed this high frequency of heterozygous FH in our pediatric population with hypercholesterolemia, none of the five established molecular defects for the French-Canadian population was detected in 29% of the unrelated French-Canadian children characterized by a persistent increase in LDL (low density lipoprotein receptor) cholesterol and a positive parental history of hyperlipidemia (Assouline et al., 1995). To probe for new mutations, six of these molecularly undiagnosed children were investigated as index patients. By using single-strand conformation polymorphism analysis and DNA sequencing, two novel mutations were identified in two of these subjects: (1) 7-base pair (bp) duplication following nucleotide 681 (according to the cDNA sequence) in exon 4 (681ins7), which causes a frameshift, the introduction of a stop at codon 208, and premature chain termination, and (2) A to G change in exon 8 substituting a tyrosine for a cysteine at amino acid 354 (Y354C). A third subject carried the recently reported exon 10 mutation (Y468X), whereas the remaining three patients demonstrated various known polymorphisms with no effect on gene product. Rapid molecular assays were developed to detect the two new mutations as well as the Y468X mutation. Screening of our cohort showed heterozygosity in 1/88, in 2/88, and in 2/88 of patients for the 681ins7, the Y354C, and the Y468X mutations, respectively.

Software and database for the analysis of mutations in the human LDL receptor gene

The low-density lipoprotein receptor (LDLr) plays a pivotal role in cholesterol homeostasis. Mutations in the LDLr gene (LDLR), which is located on chromosome 19, cause familial hypercholesterolemia (FH), an autosomal dominant disorder characterized by severe hypercholesterolemia associated with premature coronary atherosclerosis. To date almost 300 mutations have been identified in the LDLR gene. To facilitate the mutational analysis of the LDLR gene, and promote the analysis of the relationship between genotype and phenotype, a software package along with a computerized database (currently listing 210 entries) have been created.