Detection of MTRR 66A-->G polymorphism using the real-time polymerase chain reaction machine LightCycler for determination of composition of allele after restriction cleavage.

The MTRR gene codes for methionine synthase reductase, one of the enzymes involved in the conversion of homocysteine to methionine. This conversion influences the overall level of total plasma homocysteine (tHcy) and mutations, which reduces the enzyme activity and results in an increased concentration of tHcy. A high homocysteine level is a well-documented independent risk factor for cardiovascular disease. A polymorphism in the gene for methionine synthase reductase (MTRR 66 A>G) has been shown to be associated with the risk of giving birth to a child with Down's syndrome, and the risk of having a foetus with neural tube defects. We have established a method for analysing MTRR 66A>G on DNA from dried blood spots using melting temperature analysis. The DNA was extracted from dried blood spots using a fast procedure by boiling only.

One short well conserved region of Alu-sequences is involved in human gene rearrangements and has homology with prokaryotic chi.

Alu elements have repeatedly been found involved in gene rearrangements in humans. Although these elements have been suggested to stimulate gene rearrangements, sparse information is available for the possible mechanism(s) of these events. Here we present a compilation of Alu elements that have been involved in recombinational events leading to gene rearrangements, indicating the presence of a common 26 bp core sequence at or close to the sites of recombination. Besides the obvious possibility of retrotransposition, gene rearrangements may be induced by sequences that stimulate genetic recombination. We suggest that the core sequence stimulates recombination and may thereby cause the frequent involvement of these elements in gene rearrangements. Curiously, the core sequence contains the pentanucleotide motif CCAGC, which is also part of chi, an 8 bp sequence known to stimulate recBC mediated recombination in Escherichia coli.

DNA deletions in the low density lipoprotein (LDL) receptor gene in Danish families with familial hypercholesterolemia.

DNA samples from 25 unrelated Danish patients with familial hypercholesterolemia (FH) were screened by Southern blot hybridization to detect gross alterations in the low density lipoprotein (LDL) receptor gene. Three FH-patients were found to have a deletion. Two of these delete part of the cysteine rich domain, which comprises the ligand binding region of the LDL-receptor. The third deletion encompasses coding regions for the cytoplasmic part of the receptor. As two of these deletions could be equivalent to previously described LDL-receptor gene alterations, these data seem to support a notion of recombination hot spots which involve Alu-sequences.

Repetitive sequences involved in the recombination leading to deletion of exon 5 of the low-density-lipoprotein receptor gene in a patient with familial hypercholesterolemia.

Alu sequences in the low-density-lipoprotein (LDL) receptor gene are suspected of being of importance for the creation of gene defects leading to familial hypercholesterolemia (FH). One potential mechanism is that Alu sequences undergo homologous recombination, producing deletions or duplications of DNA segments on genomic DNA. In at least four cases (FH626, PO, JA and FH-DK3), a deletion of exon 5 of the LDL receptor gene has been reported. Only one of these (FH626) have so far been characterized in detail by sequence analysis and shown to involve two of the Alu repeated sequences, which are present in introns 4 and 5. We here report the complete characterization of FH-DK3 and show that the cross-over break points involve sequences similar, but not at identical positions in the 5' end, to those reported for FH626. The recombinations in both FH-DK3 and FH626 are suggested to have occurred within a 22-bp repeated sequence found in both junction alleles.