Double-strand breaks in the myotonic dystrophy type 1 and the fragile X syndrome triplet repeat sequences induce different types of mutations in DNA flanking sequences in Escherichia coli

The putative role of double-strand breaks (DSBs) created in vitro by restriction enzyme cleavage in or near CGG•CCG or CTG•CAG repeat tracts on their genetic instabilities, both within the repeats and in their flanking sequences, was investigated in an Escherichia coli plasmid system. DSBs at TRS junctions with the vector generated a large number of mutagenic events in flanking sequences whereas DSBs within the repeats elicited no similar products. A substantial enhancement in the number of mutants was caused by transcription of the repeats and by the absence of recombination functions (recA(−), recBC(−)). Surprisingly, DNA sequence analyses on mutant clones revealed the presence of only single deletions of 0.4–1.6 kb including the TRS and the flanking sequence from plasmids originally containing (CGG•CCG)(43) but single, double and multiple deletions as well as insertions were found for plasmids originally containing (CTG•CAG)(n) (where n = 43 or 70). Non-B DNA structures (slipped structures with loops, cruciforms, triplexes and tetraplexes) as well as microhomologies are postulated to participate in the recombination and/or repair processes

Absence of MutSβ leads to the formation of slipped-DNA for CTG/CAG contractions at primate replication forks

Typically disease-causing CAG/CTG repeats expand, but rare affected families can display high levels of contraction of the expanded repeat amongst offspring. Understanding instability is important since arresting expansions or enhancing contractions could be clinically beneficial. The MutSβ mismatch repair complex is required for CAG/CTG expansions in mice and patients. Oddly, by unknown mechanisms MutSβ-deficient mice incur contractions instead of expansions. Replication using CTG or CAG as the lagging strand template is known to cause contractions or expansions respectively; however, the interplay between replication and repair leading to this instability remains unclear. Towards understanding how repeat contractions may arise, we performed in vitro SV40-mediated replication of repeat-containing plasmids in the presence or absence of mismatch repair. Specifically, we separated repair from replication: Replication mediated by MutSβ- and MutSα-deficient human cells or cell extracts produced slipped-DNA heteroduplexes in the contraction- but not expansion-biased replication direction. Replication in the presence of MutSβ disfavoured the retention of replication products harbouring slipped-DNA heteroduplexes. Post-replication repair of slipped-DNAs by MutSβ-proficient extracts eliminated slipped-DNAs. Thus, a MutSβ-deficiency likely enhances repeat contractions because MutSβ protects against contractions by repairing template strand slip-outs. Replication deficient in LigaseI or PCNA-interaction mutant LigaseI revealed slipped-DNA formation at lagging strands. Our results reveal that distinct mechanisms lead to expansions or contractions and support inhibition of MutSβ as a therapeutic strategy to enhance the contraction of expanded repeats

Sexual function following treatment for carcinoma of cervix

A retrospective study of the changes in sexual function of 103 Chinese patients after treatment for carcinoma of cervix was done. Ten patients were irradiated, 40 patients were treated by surgery and 53 patients received both surgery and irradiation. Changes in sexual function were noted in all 3 groups. Patients who had undergone major operation were reluctant to resume sexual intercourse because of cultural beliefs and erroneous ideas regarding sex, surgery and cancer. It is proposed that radiotherapy might be a better form of treatment for some of these patients.link_to_subscribed_fulltex

Comparison of four different dosages of injectable bromocriptine retard for puerperal ablactation

The clinical efficacy, tolerance and effect on plasma prolactin levels of four different dosages of intramuscular bromocriptine retard were compared. 108 Chinese puerperas with a mean body weight of 58 kg, who chose not to breast-feed following vaginal delivery, were randomized into four equal groups. The patients in each group were given intramuscular bromocriptine retard: 20, 30, 40 or 50 mg. The injection was well tolerated by all, except for two patients who developed small haematomas at the site of the injection and 2 patients who complained of dizziness. Ablactation occurred in 100% of the patients in the 40 mg group, but was successful in only 92 and 91% of the patients in the 20 and 30 mg groups, respectively. There were two cases of suboptimal response in the 50 mg group, despite marked reduction in plasma prolactin levels. Both these patients had developed moderate breast engorgement before they received the injection. The difference in response among the four groups was not statistically significant. We recommend that the injection be given prior to the development of breast engorgement.link_to_subscribed_fulltex