The molecular basis of familial hypercholesterolaemia in Turkish patients.

Familial hypercholesterolaemia (FH) is an autosomal dominant disorder of lipoprotein metabolism. In the majority of patients FH is caused by mutations in the gene for the low-density lipoprotein receptor (LDLR), and to date more than 700 mutations have been reported worldwide. In this study, 36 paediatric patients with a clinical diagnosis of FH (20 homozygous and 16 heterozygotes) were screened for mutations in the LDLR gene. Each exon, with intron-exon junctions, was screened by capillary fluorescent SSCP (F-SSCP) and heteroduplex analysis. Samples showing different band patterns were sequenced. Ten novel (including three frame shift small deletions or insertions) and seven known mutations were detected. A total of 37 out of the predicted 56 FH-causing alleles were identified (66.1%). No patients with the R3500Q mutation in the APOB gene were found. W556R was the most common mutation, explaining 21.4% of the predicted defective LDLR alleles. The novel sequence changes were deemed to be pathogenic if they altered a conserved amino acid (L143P, D147E, Q233H-C234G, C347G) or occurred in or close to a splice site (IVS 16+5) and were absent in DNA from 50 healthy Turkish subjects. These data confirm the genetic heterogeneity of FH in Turkey, and demonstrate the usefulness of F-SSCP for mutation detection.

Mitochondrial DNA sequence variation in the Anatolian Peninsula (Turkey).

Throughout human history, the region known today as the Anatolian peninsula (Turkey) has served as a junction connecting the Middle East, Europe and Central Asia, and, thus, has been subject to major population movements. The present study is undertaken to obtain information about the distribution of the existing mitochondrial D-loop sequence variations in the Turkish population of Anatolia. A few studies have previously reported mtDNA sequences in Turks. We attempted to extend these results by analysing a cohort that is not only larger, but also more representative of the Turkish population living in Anatolia. In order to obtain a descriptive picture for the phylogenetic distribution of the mitochondrial genome within Turkey, we analysed mitochondrial D-loop region sequence variations in 75 individuals from different parts of Anatolia by direct sequencing. Analysis of the two hypervariable segments within the noncoding region of the mitochondrial genome revealed the existence of 81 nucleotide mutations at 79 sites. The neighbour-joining tree of Kimura's distance matrix has revealed the presence of six main clusters, of which H and U are the most common. The data obtained are also compared with several European and Turkic Central Asian populations.

Genetically heterogeneous selective intestinal malabsorption of vitamin B12: founder effects, consanguinity, and high clinical awareness explain aggregations in Scandinavia and the Middle East.

Selective intestinal malabsorption of vitamin B(12) causing juvenile megaloblastic anemia (MGA; MIM# 261100) is a recessively inherited disorder that is believed to be rare except for notable clusters of cases in Finland, Norway, and the Eastern Mediterranean region. The disease can be caused by mutations in either the cubilin (CUBN; MGA1; MIM# 602997) or the amnionless (AMN; MIM# 605799) gene. To explain the peculiar geographical distribution, we hypothesized that mutations in one of the genes would mainly be responsible for the disease in Scandinavia, and mutations in the other gene in the Mediterranean region. We studied 42 sibships and found all cases in Finland to be due to CUBN (three different mutations) and all cases in Norway to be due to AMN (two different mutations), while in Turkey, Israel, and Saudi Arabia, there were two different AMN mutations and three different CUBN mutations. Haplotype evidence excluded both CUBN and AMN conclusively in five families and tentatively in three families, suggesting the presence of at least one more gene locus that can cause MGA. We conclude that the Scandinavian cases are typical examples of enrichment by founder effects, while in the Mediterranean region high degrees of consanguinity expose rare mutations in both genes. We suggest that in both regions, physician awareness of this disease causes it to be more readily diagnosed than elsewhere; thus, it may well be more common worldwide than previously thought.

Effects of neutral, cationic, and anionic chromium ascorbate complexes on isolated human mitochondrial and genomic DNA.

The relative activities of neutral, cationic, and anionic chromium ascorbate complexes toward isolated human mitochondrial and genomic DNA were investigated at physiologically relevant conditions by agarose gel electrophoresis. A direct relationship between the charge of the Cr(III) species and their DNA-damaging properties was found. The cationic species were found to be fully capable of DNA-cleavage, even in short incubation periods. Incubations were also performed in the presence of amino acids. No apparent effect was observed under the applied experimental conditions to facilitate or prevent damage through the ternary amino acid-Cr-DNA adduct formation or binary chromium-amino acid complex formation.

Identification of an inframe deletion and a missense mutation in the factor XIIIA gene in two Turkish patients.

We report two novel mutations in factor XIIIA (FXIIIA) gene that caused congenital factor XIII deficiency in two unrelated patients. The first alteration, a missense mutation Leu235Arg in exon 6 of FXIIIA gene, is located in the putative calcium-binding part of the core domain of the enzyme. Replacement of non-polar hydrophobic leucine residue with positively charged arginine residue is likely to effect protein folding thus destabilizing the molecule. The second mutation is a 3-bp deletion in exon 14 of FXIIIA gene. This deletion is located in beta barrel 2 domain of the protein and results in translation of an aberrant FXIIIA molecule that lacks lysine residue either at positions 677 or 678. As this inframe deletion is located in a direct repetetive sequence of AAGAAG, that codes for two lysine residues, the exact location of deletion could not be detected.

Mutations in coagulation factor XIII A gene in three Turkish patients: two novel mutations and a known insertion.

Molecular analysis of factor XIII A gene on three unrelated Turkish families identified two novel and one known mutations. One novel mutation is a substitution of cytidine by guanine at codon 541 in exon 12, beta barrel 1 domain of the coagulation factor XIII A subunit gene resulting in the conversion of asparagine to lysine. The mutation alters the restriction site of the enzyme MboII. The second novel mutation, a 4 bp (-CAAA) deletion located in a direct repetitive sequence (CAAACAAA) between codons 466-469, results in premature termination of translation at codon 474. The third mutation is a previously reported single nucleotide (cytidine) insertion at codon 400 in exon 9 of the factor XIII gene.