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Screening for mutations in the muscle promoter region and for exonic deletions in a series of 115 DMD and BMD patients.

Mutations in the muscle promoter region and exonic deletions were screened in a series of 115 unrelated DMD and BMD patients from north-east Italy. No gross mutations of the promoter region were found. In three cases in which dystrophin of normal size was expressed at low levels, the analysis of DNA sequences of the promoter region failed to detect abnormalities. The majority of deletions in coding sequences, detected by cDNA probes, occur in the deletion hot spot identified by the probe P20. Intrafamilial variability in the severity of the disease is reported and discussed.

Adolescent↗

Alternative splicing of dystrophin mRNA complicates carrier determination: report of a DMD family.

Carrier determination is important for genetic counselling in DMD/BMD families. The detection of altered PCR amplified dystrophin mRNA fragments owing to deletions, insertions, or point mutations has increased the possibilities of carrier determination. However, problems may occur because of alternative splicing events. Here we present a family with a DMD patient characterised by a deletion of exons 45 to 54. At the mRNA level we detected a corresponding altered fragment which served for carrier determination. The mother and the sister of the patient showed the same altered dystrophin mRNA fragment as the patient and are therefore carriers. In the mother two additional altered dystrophin mRNA fragments were detectable, obviously resulting from alternative splicing in the normal allele. The grandmother and two other related females of the patient possess only the normal mRNA fragment. In a further female we detected an altered fragment owing to an mRNA deletion of exon 44. This fragment is created either by alternative splicing or a new mutation. Therefore, the carrier status of this female is still ambiguous indicating problems in carrier determination by the method of dystrophin mRNA analysis.

Alternative Splicing↗

Copy number variation in the genome; the human DMD gene as an example.

Recent developments have yielded new technologies that have greatly simplified the detection of deletions and duplications, i.e., copy number variants (CNVs). These technologies can be used to screen for CNVs in and around specific genomic regions, as well as genome-wide. Several genome-wide studies have demonstrated that CNV in the human genome is widespread and may include millions of nucleotides. One of the questions that emerge is which sequences, structures and/or processes are involved in their generation. Using as an example the human DMD gene, mutations in which cause Duchenne and Becker muscular dystrophy, we review the current data, determine the deletion and duplication profile across the gene and summarize the information that has been collected regarding their origin. In addition we discuss the methods most frequently used for their detection, in particular MAPH and MLPA.

Alleles↗

[Dystrophin and utrophin expression in muscle tissues of DMD mouse model after transplantation treatment by bone marrow mesenchymal stem cells].

OBJECTIVE: To observe dystrophin and utrophin expression in muscle tissues of Duchenne muscular dystrophy (DMD) mouse model (dko mouse) after having been treated with bone marrow mesenchymal stem cells (MSC) transplantation. METHODS: The fifth generation of MSCs, cultured in vitro, was transplanted into dko mice by tail vein. The fluorescent expression of dystrophin and utrophin in gastrocnemius muscle tissue of dko mouse was detected and the average optical density of positive fibers was calculated. RESULTS: MSCs that had been cultured for three generations had good homogeneousness and the immunological reaction after vein transplantation was low. There was an increasing tendency of dystrophin and utrophin fluorescent expression in sarcolemma of dko mouse within 5-20 weeks. Significant difference existed in fluorescent average optical density of positive fibers fifteen weeks before and after cell transplantation. CONCLUSIONS: MSC has strong plasticity both in vitro and in vivo. MSC has a trend to reach the injured muscle tissues and turn into muscle fibers, which express dystrophin and utrophin. There is some plerosis function for myatrophy of dko mouse by MSC transplantation.

Animals↗

[Bayesian and RFLP linkage analysis on a DMD family].

Three methods were applied to estimate the carrier risk of the daughter of an obligate carrier of the Duchenne gene in a pedigree of Duchenne muscular dystrophy (DMD). According to Mendel's law of segregation, the daughter (III-3) of the obligate carrier (II-2) has a 50% chance of being a carrier. III-3 is also found to have a normal value in a carrier test, creatine phosphate kinase (CPK), and so the Bayesian analysis in risk estimation shows that the posterior probability that she is a carrier (25%). The restriction fragment length polymorphism (RFLP) linkage analysis indicates that the probability that III-3 is a carrier less than 5%. This result can be included in the Bayesian analysis to give an even lower risk of less than 2%. Our study demonstrates that the best result of carrier risk estimation can be obtained by a simultaneous application of Mendel's law, RFLP linkage analysis and the Bayesian analysis.

Bayes Theorem↗

Intragenic deletions in 21 Duchenne muscular dystrophy (DMD)/Becker muscular dystrophy (BMD) families studied with the dystrophin cDNA: location of breakpoints on HindIII and BglII exon-containing fragment maps, meiotic and mitotic origin of the mutations.

Following the strategy outlined in an accompanying paper, we studied 32 X-linked muscular dystrophy families (29 Duchenne [DMD] and three Becker [BMD] type) for abnormalities of HindIII and BglII fragments detected by the entire dystrophin cDNA. Twenty-one different single-intragenic deletions, and no duplications, were identified. The deletion endpoints were precisely mapped on the published HindIII fragment map. Detailed analysis of overlapping deletions led to clarification of the fragment order for some previously unsettled regions of the HindIII map and to the construction of a partial map of exon-containing BglII fragments. For the regions involved in deletions, the corresponding HindIII and BglIII fragments could be identified. Noncontiguous comigrating fragments were detected in two regions by careful analysis of the patterns in deletion patients. Four of the 21 deletions generated novel restriction fragments that facilitated detection of female carriers in these families. Twelve of the deletions had a breakpoint in one of the two large introns known to be the sites of breakpoint clusters. By combining deletions and RFLP analyses, we unequivocally identified the gamete that first carried the mutation in 13 families: eight oocytes and five sperm. Germ-line mosaicism previously detected in one male was confirmed by cDNA studies. In two additional families gonadal mosaicism was found in females. As evidence is accumulating for frequent mitotic origin of these deletion mutations, this phenomenon has to be considered when postulating mutational mechanisms and in genetic counseling of DMD/BMD families.

Bacterial Proteins↗

[Genetic analysis of 60 Duchenne muscular dystrophy (DMD) or Becker muscular dystrophy (BMD) patients using dystrophin cDNA].

We have studied 60 unrelated Chinese Duchenne muscular dystrophy (DMD) or Becker muscular dystrophy (BMD) patients using dystrophin cDNA. Thirty-two mutations (53%) were detected, 31 deletions and 1 duplication. The major deletion-rich region is located in the center of the dystrophin locus. This region includes the last four exons covered by cDNA 5b-7 and all exons detected by cDNA 8. No correlation was observed between the location or length of the deletions and the clinical phenotypes of the patients.

Asian People↗

Pyruvate-kinase (PK) and creatine-kinase (CK) in normal pregnancy and its implication in genetic counseling of Duchenne muscular dystrophy (DMD).

The activities of pyruvate-kinase (PK) and creatine-kinase (CK) were measured in 50 normal pregnant women in both serum and amniotic fluid. Serum PK activity was found to be significantly higher in pregnant than in nonpregnant women, while serum CK did not differ significantly between the two population samples. In amniotic fluid, very little or no PK or CK activity was found. However, the mean PK activity in amniotic fluid obtained from women carrying male fetuses was significantly higher than in those carrying female fetuses. At the present time, it is concluded that if a woman at risk for having a son with Duchenne dystrophy is seeking genetic counseling when already pregnant her serum PK or CK should be compared with that of normal female pregnant controls. It is also suggested that determination of pyruvate-kinase in fetal blood might be used in addition to CK for prenatal diagnosis of Duchenne muscular dystrophy.

Adult↗

Parental attitudes regarding newborn screening of PKU and DMD.

The ability to perform predictive genetic testing of children raises ethical concerns. Current guidelines support the screening of newborns for conditions in which early treatment reduces morbidity and mortality, and oppose most other predictive genetic screening and testing in childhood. Little is known, however, about parental attitudes. We conducted focus groups to gain information on the attitudes, beliefs, and concerns of parents about newborn screening and testing for both treatable and untreatable conditions that present in childhood. Respondents across racial groups support mandatory newborn screening for treatable conditions like phenylketonuria (PKU), citing lack of parental knowledge, and concerns about immature parental decision-makers. Parents do, however, want more information. Citing a variety of psychosocial concerns, respondents believe that parents should have access to predictive genetic testing for childhood onset conditions, even when there are no proven treatments. Respondents want this information to make reproductive and non-reproductive plans and decisions. Although respondents varied in their personal interest in testing, overwhelmingly they believed that the decisions belong to the parents. Professional guidelines that proscribe predictive testing for untreatable childhood onset conditions should be re-examined in light of consumer attitudes.

Age of Onset↗

Transplantation of normal and DMD myoblasts expressing the telomerase gene in SCID mice.

The limited proliferative capacity of dystrophic human myoblasts severely limits their ability to be genetically modified and used for myoblast transplantation. The forced expression of the catalytic subunit of telomerase can prevent telomere erosion and can immortalize different cell types. We thus tested the ability of telomerase to immortalize myoblasts and analyzed the effect of telomerase expression on the success of myoblast transplantation. Telomerase expression did not significantly extend the human myoblast life span. The telomerase expressing myoblasts were nonetheless competent to participate in myofiber formation after infection with the retroviral vector. Although the new fibers obtained are less numerous than after the transplantation of normal myoblasts, these results demonstrate that the forced expression of telomerase does not block the ability of normal or dystrophic myoblasts to differentiate in vivo. It will be now necessary to determine the factors that prevent telomerase from extending the life span of human myoblasts before the potential of this intervention can be fully examined.

Animals↗

Immune response to full-length dystrophin delivered to Dmd muscle by a high-capacity adenoviral vector.

Adenoviral vector-mediated gene transfer to skeletal muscle is a promising potential treatment for Duchenne muscular dystrophy. However, the immunological response to viral antigens and the therapeutic protein expressed by the delivered gene could prevent effective treatment. In this study, we investigated the immune response induced by adenoviral and dystrophin antigens presented by high-capacity adenoviral vector-mediated dystrophin and beta-galactosidase delivery to skeletal muscle of a mouse model that is both dystrophin-deficient and lacZ transgenic. Direct intramuscular gene delivery of the high-capacity adenoviral vector encoding full-length murine dystrophin resulted in stable expression of recombinant dystrophin for 5 months in mice treated as neonates and for 4 weeks in mice treated as adults. We observed neutralizing antibody to adenoviral antigens only in mice treated as adults and not in mice treated as neonates. This suggested that adenoviral antigens were only presented at the time of vector administration when the neonatal immune system was not yet mature. In contrast, antibodies to dystrophin were observed both in mice treated as neonates and in mice treated as adults. The development of an anti-dystrophin antibody response in mice treated with the high-capacity adenoviral vector as neonates suggested that dystrophin antigens were presented to the immune system at a time remote from the gene delivery, when the immune system was mature. Interestingly, an antibody response against beta-galactosidase developed late in the course of mice treated with the high-capacity adenoviral vector as neonates, suggesting a loss of tolerance to beta-galactosidase, a self-antigen in these transgenic mice. Our results suggest that future human trials of dystrophin gene delivery will need to address the potential for immunity induced by ongoing segmental degeneration of partially treated muscle fibers and presentation of recombinant dystrophin antigens in the context of a Duchenne muscular dystrophy patient.

Animals↗