Two novel partial deletions of LDL-receptor gene in Italian patients with familial hypercholesterolemia (FH Siracusa and FH Reggio Emilia)

A novel mutation in the sterol 27-hydroxylase gene of a woman with autosomal recessive cerebrotendinous xanthomatosis

Mutations of the gene encoding the mitochondrial enzyme sterol 27-hydroxylase (CYP27A1 gene) cause defects in the cholesterol pathway to bile acids that lead to the storage of cholestanol and cholesterol in tendons, lenses and the central nervous system. This disorder is the cause of a clinical syndrome known as cerebrotendinous xanthomatosis (CTX). Since 1991 several mutations of the CYP27A1 gene have been reported. We diagnosed the clinical features of CTX in a caucasian woman. Serum levels of cholestanol and 7α-hydroxycholesterol were elevated and the concentration of 27-hydroxycholesterol was reduced. Bile alcohols in the urine and faeces were increased. The analysis of the CYP27A1 gene showed that the patient was a compound heterozygote carrying two mutations both located in exon 8. One mutation is a novel four nucleotide deletion (c.1330-1333delTTCC) that results in a frameshift and the occurrence of a premature stop codon leading to the formation of a truncated protein of 448 amino acids. The other mutation, previously reported, is a C - > T transition (c. c.1381C > T) that converts the glutamine codon at position 461 into a termination codon (p.Q461X). These truncated proteins are expected to have no biological function being devoid of the cysteine residue at position 476 of the normal enzyme that is crucial for heme binding and enzyme activity.

A novel mutation in the sterol 27-hydroxylase gene of a woman with autosomal recessive cerebrotendinous xanthomatosis

Article abstract

Mutations of the gene encoding the mitochondrial enzyme sterol 27-hydroxylase (CYP27A1 gene) cause defects in the cholesterol pathway to bile acids that lead to the storage of cholestanol and cholesterol in tendons, lenses and the central nervous system. This disorder is the cause of a clinical syndrome known as cerebrotendinous xanthomatosis (CTX). Since 1991 several mutations of the CYP27A1 gene have been reported. We diagnosed the clinical features of CTX in a caucasian woman. Serum levels of cholestanol and 7α-hydroxycholesterol were elevated and the concentration of 27-hydroxycholesterol was reduced. Bile alcohols in the urine and faeces were increased. The analysis of the CYP27A1 gene showed that the patient was a compound heterozygote carrying two mutations both located in exon 8. One mutation is a novel four nucleotide deletion (c.1330-1333delTTCC) that results in a frameshift and the occurrence of a premature stop codon leading to the formation of a truncated protein of 448 amino acids. The other mutation, previously reported, is a C - > T transition (c. c.1381C > T) that converts the glutamine codon at position 461 into a termination codon (p.Q461X). These truncated proteins are expected to have no biological function being devoid of the cysteine residue at position 476 of the normal enzyme that is crucial for heme binding and enzyme activity.

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

Background

Mutations 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.

Methods

DNA 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.

Results

In 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.

Conclusions

Sequence 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.

Large rearrangements of the LDL receptor gene and lipid profile in a FH Spanish population

BACKGROUND

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by mutations in the low-density lipoprotein receptor (LDLR) gene. To date, there has not been a systematic survey of the frequency of gross mutations in the LDLR gene in the Spanish population. The objective of our study was to investigate large rearrangements in the Spanish FH population and the relation between the kind of large rearrangement and the phenotype in carrier families.

MATERIALS AND METHODS

The LDLR gene was screened to detect major rearrangements in a sample of 89 probands. Southern blot, long polymerase chain reaction (PCR), reverse transcription (RT) -PCR and DNA sequencing were used to detect and characterize the mutations.

RESULTS

Five large rearrangements were found in six probands. Two mutations were due to duplications of internal regions of the gene, whereas the rest were caused by partial deletions, which eliminated the promoter region in two cases. The internal rearrangements, two duplications and one deletion, were apparently caused by recombination between ALU sequences and the study of their mRNA indicated that the reading frame was maintained. The analysis of the lipid profile between patients with similar characteristics (age, sex, body mass index, etc.) but carrying mutations that either eliminated the promoter region or produced internal rearrangements showed significant differences (total cholesterol: 366.6 +/- 81.8 vs. 304.6 +/- 25.1 P = 0.023, and LDL cholesterol: 317.7 +/- 65.1 vs. 249.2 +/- 27.4 P = 0.003).

CONCLUSIONS

The frequency of large mutations in a Spanish FH sample was close to 7% and at least four of the mutations found had not been described in other populations. Mutations that eliminate the promoter region originate more severe hypercholesterolemia than defective mutations, which suggests that the absence of the promoter region and transcription of the LDLR gene is worse compensated than the synthesis of a defective LDL receptor.

Clinical expression of familial hypercholesterolemia in clusters of mutations of the LDL receptor gene that cause a receptor-defective or receptor-negative phenotype

Seventy-one mutations of the low density lipoprotein (LDL) receptor gene were identified in 282 unrelated Italian familial hypercholesterolemia (FH) heterozygotes. By extending genotype analysis to families of the index cases, we identified 12 mutation clusters and localized them in specific areas of Italy. To evaluate the impact of these mutations on the clinical expression of FH, the clusters were separated into 2 groups: receptor-defective and receptor-negative, according to the LDL receptor defect caused by each mutation. These 2 groups were comparable in terms of the patients' age, sex distribution, body mass index, arterial hypertension, and smoking status. In receptor-negative subjects, LDL cholesterol was higher (+18%) and high density lipoprotein cholesterol lower (-5%) than the values found in receptor-defective subjects. The prevalence of tendon xanthomas and coronary artery disease (CAD) was 2-fold higher in receptor-negative subjects. In patients >30 years of age in both groups, the presence of CAD was related to age, arterial hypertension, previous smoking, and LDL cholesterol level. Independent contributors to CAD in the receptor-defective subjects were male sex, arterial hypertension, and LDL cholesterol level; in the receptor-negative subjects, the first 2 variables were strong predictors of CAD, whereas the LDL cholesterol level had a lower impact than in receptor-defective subjects. Overall, in receptor-negative subjects, the risk of CAD was 2.6-fold that of receptor-defective subjects. Wide interindividual variability in LDL cholesterol levels was found in each cluster. Apolipoprotein E genotype analysis showed a lowering effect of the epsilon2 allele and a raising effect of the epsilon4 allele on the LDL cholesterol level in both groups; however, the apolipoprotein E genotype accounted for only 4% of the variation in LDL cholesterol. Haplotype analysis showed that all families of the major clusters shared the same intragenic haplotype cosegregating with the mutation, thus suggesting the presence of common ancestors.

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.