Lukáš Tichý

Genomic characterization of large rearrangements of the LDLR gene in Czech patients with familial hypercholesterolemia

BackgroundMutations in the LDLR gene are the most frequent cause of Familial hypercholesterolemia, an autosomal dominant disease characterised by elevated concentrations of LDL in blood plasma. In many populations, large genomic rearrangements account for approximately 10% of mutations in the LDLR gene.MethodsDNA diagnostics of large genomic rearrangements was based on Multiple Ligation dependent Probe Amplification (MLPA). Subsequent analyses of deletion and duplication breakpoints were performed using long-range PCR, PCR, and DNA sequencing.ResultsIn set of 1441 unrelated FH patients, large genomic rearrangements were found in 37 probands. Eight different types of rearrangements were detected, from them 6 types were novel, not described so far. In all rearrangements, we characterized their exact extent and breakpoint sequences.ConclusionsSequence analysis of deletion and duplication breakpoints indicates that intrachromatid non-allelic homologous recombination (NAHR) between Alu elements is involved in 6 events, while a non-homologous end joining (NHEJ) is implicated in 2 rearrangements. Our study thus describes for the first time NHEJ as a mechanism involved in genomic rearrangements in the LDLR gene.

The logarithm of the triglyceride/HDL-cholesterol ratio is related to the history of cardiovascular disease in patients with familial hypercholesterolemia.

OBJECTIVES The aim of this study was to determine whether the atherogenic index of plasma (AIP=log[triglycerides/HDL-cholesterol]) differs in heterozygous familial hypercholesterolemia (FH) patients with and without a history of cardiovascular disease (CVD). DESIGN AND METHODS A total of 555 FH patients with known mutations in the LDL receptor or the apolipoprotein B gene, of whom 53 had a history of CVD (CVD+ group), were retrospectively analyzed. RESULTS Compared to patients without CVD (CVD- group), CVD+ patients showed significantly higher fasting LDL-cholesterol, triglycerides and AIP as well as lower HDL-cholesterol. After both adjustment for age and diabetes and using analysis based on age and sex matched groups, only the increase in triglycerides and AIP in the CVD+ vs. the CVD- group remained significant. CONCLUSION The results of the present study indicate that AIP, which reflects the presence of atherogenic small LDL and small HDL particles, may be connected to the risk of CVD in FH patients.

An APEX-based genotyping microarray for the screening of 168 mutations associated with familial hypercholesterolemia.

OBJECTIVE Familial hypercholesterolemia (FH) is an inborn disorder of lipid metabolism characterised by elevated plasma concentrations of low-density lipoprotein cholesterol and total cholesterol. This imbalance results in accelerated atherosclerosis and premature coronary heart disease. The early identification and treatment of FH patients is extremely important because it leads to significant reduction of both coronary morbidity and mortality. FH is transmitted in an autosomal dominant manner and associated predominantly with mutations in the genes encoding the low-density lipoprotein receptor (LDLR) and its ligand apolipoprotein B (APOB). To date, more than 1000 sequence variants have been described in the LDLR gene. In marked contrast to LDLR, only one APOB mutation is prevalent in Europe. METHODS AND RESULTS The aim of this study was, on the basis of data obtained by the molecular genetic analysis of 1945 Czech FH probands, to propose, generate, and validate a new diagnostic tool, an APEX (Arrayed Primer EXtension)-based genotyping DNA microarray called the FH chip. The FH chip contains the APOB mutation p.Arg3527Gln, all 89 LDLR point mutations and small DNA rearrangements detected in Czech FH patients, and 78 mutations frequent in other European and Asian FH populations. The validation phase revealed the sensitivity and specificity of this platform, 100% and 99.1%, respectively. CONCLUSIONS This FH chip is a rapid, reproducible, specific, and cost-effective tool for genotyping, and in combination with MLPA (multiple ligation-dependent probe amplification) represents a reliable molecular genetic protocol for the large-scale screening of FH mutations in the Czech population.

Functional analysis of the p.(Leu15Pro) and p.(Gly20Arg) sequence changes in the signal sequence of LDL receptor

The low density lipoprotein receptor (LDLR) is a transmembrane protein that plays a key role in cholesterol metabolism. It contains 860 amino acids including a 21 amino acid long signal sequence, which directs the protein into the endoplasmic reticulum. Mutations in the LDLR gene lead to cholesterol accumulation in the plasma and results in familial hypercholesterolemia (FH). Knowledge of the impact of a mutation on the LDLR protein structure and function is very important for the diagnosis and management of FH. Unfortunately, for a large proportion of mutations this information is still missing. In this study, we focused on the LDLR signal sequence and carried out functional and in silico analyses of two sequence changes, p.(Gly20Arg) and p.(Leu15Pro), localized in this part of the LDLR. Our results revealed that the p.(Gly20Arg) change, previously described as disease causing, has no detrimental effect on protein expression or LDL particle binding. In silico analysis supports this observation, showing that both the wt and p.(Gly20Arg) signal sequences adopt an expected α-helix structure. In contrast, the mutation p.(Leu15Pro) is not associated with functional protein expression and exhibits a structure with disrupted a α-helical arrangement in the signal sequence, which most likely affects protein folding in the endoplasmic reticulum.