Detection of dystrophin deletion carriers using FISH analysis

Development of a comprehensive real-time PCR assay for dystrophin gene analysis and prenatal diagnosis of Chinese families

BACKGROUND

To develop a comprehensive method to analyze deletions or duplications of the dystrophin gene in both patients and carriers of Duchenne muscular dystrophy (DMD), likewise applied to prenatal diagnosis.

METHODS

A total of thirty Chinese families were recruited, composed of 29 DMD affected males and 38 female relatives containing four pregnant women. Deletions were previously screened by multiplex PCR. A comprehensive real-time PCR assay using SYBR Green I dye was performed for the initial detection of duplications in patients with a seven-exon primer set, carrier detection for female relatives and prenatal diagnosis for the 4 of them. The results were later confirmed by multiple ligation-dependent probe amplification (MLPA) and linkage analysis.

RESULTS

Three out of 4 duplications were first discovered by real-time PCR. Carrier status was ascertained in 22 and rejected in the remaining sixteen female relatives. Furthermore, 4 fetuses were diagnosed as two normal females, one normal male and one female carrier, respectively.

CONCLUSIONS

Our real-time PCR assay is useful in duplication screen with a detection rate of >70%, as well as rapid and reliable in both carrier detection and prenatal diagnosis of DMD families with known deletions and duplications.

Experience and strategy for the molecular testing of Duchenne muscular dystrophy

Mutations in the dystrophin gene result in both Duchenne and Becker muscular dystrophies (DMD and BMD). Approximately two-thirds of the affected patients have large deletions or duplications. Using the multiplex polymerase chain reaction and Southern blotting techniques, the detection of these larger mutations is relatively straightforward. Detection of the point mutations in the remaining one-third of the patients has been challenging, mainly due to the large gene size and lack of hotspots or prevalent mutations. However, with the addition of some of the newer molecular screening methods, it is becoming more feasible for clinical laboratories to test for point mutations in the larger genes like dystrophin. Here we review the clinical features, describe the mutation distributions, evaluate current molecular strategies, and illustrate how the genetic findings have impacted the current clinical diagnostics of Duchenne and Becker muscular dystrophies.

Screening for DMD/BMD Deletion Carriers by FluorescenceIn SituHybridization

Fluorescence in situ hybridization (FISH) serves as an excellent alternative for direct detection of heterozygous deletions. Using a set of exon-specific cosmid DNA probes representing 18 exons, one-color FISH on metaphase and interphase preparations was performed to identify Duchenne/Becker muscular dystrophy (DMD/BMD) deletion carriers. The peripheral blood samples from 9 normal male or female controls and 5 females of independent DMD/BMD families, as well as 2 amniotic fluid specimens and 2 chorionic villus samples (CVS) from normal pregnant females, were analyzed. Expected signals were displayed in 72-100% of peripheral blood lymphocyte metaphases or interphases, 60-70% of amniocyte interphases, and 95-99% of chorionic villus cell interphases. One suspected female was identified as a deletion carrier and two were excluded. The results indicated that metaphase and interphase FISH were both useful for detection of heterozygous deletions. FISH, in combination with other available techniques, allowed efficient screening of DMD/BMD deletion carriers. The study also offered preliminary results in support of an approach to prenatal diagnosis of potential fetal carriers.

Carrier detection and prenatal molecular diagnosis in a Duchenne muscular dystrophy family without any affected relative available

In this paper we report a family where the affected DMD patients were not available for study and a molecular strategy was used for female carriers detection and for prenatal diagnosis. Linkage analysis was performed with two markers within the DMD gene, in all family members screened. DMD markers used (pERT87.8/Taq1 and pERT87.15/Xmn1) seemed not to be informative because the propositas mother (II-2) was homozygous for the minor allele at each marker (T2 and X2), however, the proposita and one sister carried only the major allele, which was inherited from the father. These results suggested that a deletion involving both markers could be present, and was inherited from the mother to both daughters. Quantitative multiplex PCR confirmed the deletion in female carriers, involving at least exons 12 to 17. DNA studies of cultured amniotic fluid cells at 14 weeks gestation, by amplification of specific Y-chromosome sequences, followed by multiplex PCR, lead to the diagnosis of a male fetus affected by DMD.

Molecular analysis of a spontaneous dystrophin 'knockout' dog

We have determined the molecular basis for skeletal myopathy and dilated cardiomyopathy in two male German short-haired pointer (GSHP) littermates. Analysis of skeletal muscle demonstrated a complete absence of dystrophin on Western blot analysis. PCR analysis of genomic DNA revealed a deletion encompassing the entire dystrophin gene. Molecular cytogenetic analysis of lymphocytes from the dam and both dystrophic pups confirmed a visible deletion in the p21 region of the affected canine X chromosome. Utrophin is up-regulated in the skeletal muscle, but does not appear to ameliorate the dystrophic canine phenotype. This new canine model should further our understanding of the physiological and biochemical processes in Duchenne muscular dystrophy.