Possibilities and limitation of prenatal diagnosis and carrier determination for Duchenne and Becker muscular dystrophy using cDNA probes.

Abstract

SUMMARY Two cDNA probes, cf23a and cf56a, identify deletions of selected exons in about 50% of our DMD/BMD patients. We have estimated the most likely order of the 11 exons detectable with both probes with respect to the different extensions of the deletions. In one of our BMD pedigrees, the observed deletion could be traced in the affected males through three generations. This result shows that with the use of cDNA probes detecting deletions, the only risk of error in genomic prenatal diagnosis is the general high frequency of new mutations for DMD/BMD. This is important progress in diagnosis compared to the 2 to 5% risk of misdiagnosis 'because of crossing over events using conventional linkage analysis with bridging or intragenic probes. The first prenatal diagnosis of an unaffected fetus of a woman who is a DMD carrier according to ultrasound examination is described. In one of our DMD males, the cDNA probe cf56a detects a deletion breakpoint. His sister also shows the altered band and is therefore a DMD carrier, while his mother has a totally normal band pattern. The interpretation of this observation could be either germline mosaicism or two identical new mutations. The identification of deletion breakpoints is a new diagnostic strategy, especially for carrier determination, which excludes misdiagnosis owing to crossing over events and the problems of dosage estimation. It is, however, limited by the low frequency of breakpoints detectable with cDNA probes. Therefore, the generation of new intron probes in this region is an important goal.Duchenne muscular dystrophy (DMD) and its clinically milder allelic form, Becker muscular dystrophy (BMD), are the most common X linked recessive genetic disorders affecting about one in 3000 males. DNA diagnosis has resulted in dramatic progress in carrier detection and prenatal analysis for affected families.1-3 However, since up to now it has been predominantly based on linkage analyses, its reliability was limited by the possibility of crossing over events. This has caused difficulties in decision making for pregnant women, particularly in prenatal diagnosis.

Genotype-phenotype correlation and germline mosaicism in DMD/BMD patients with deletions of the dystrophin gene

“…(Koenig et al 1987(Koenig et al , 1989Darras et al 1988b;Wapenaar et al 1988;Baumbach et al 1989;Lindl6f et al 1989). Accurate prenatal diagnosis and carrier detection based on deletion analysis is possible by Southern blotting using eDNA or genomic probes and by PCR (Darras et al 1988a;Cole et al 1988;Speer et al 1989;Chamberlain et al 1988Chamberlain et al , 1989Chamberlain et al , 1990.…”

DMD carrier detection in a female with mosaic Turner's syndrome.

“…On the autoradiograph obtained after the usual exposure time, the DNA sample Although the aim of this study was to detect DMD carrier females in this family, the finding reported here prompts us to emphasise two points: as cDNA probes are now often used in a large number of laboratories for DMD carrier detection,2 3 we suggest that when confronted with unusual band intensities, a karyotypic abnormality should be considered. In addition, laboratories dealing with blood samples alone need as much clinical and cytogenetic data as possible, in order to make a better molecular diagnosis.…”

“…In the study of one such family using 2 7 probe 8, a deletion of the 1-25, 3-8, [1][2][3][4][5][6], and 3-7 kb HindIII fragments was seen in a boy with DMD. Visual inspection of the intensity of the 3 8 and 3 7 kb ( 6 bands diagnosed subjects 1, 3, and 6 as non-carrier females and subjects 2, 4, and 5 as DMD carriers (fig 4 1).…”

Identification of carriers of Duchenne/Becker muscular dystrophy by a novel method based on detection of junction fragments in the dystrophin gene.

“…Studies using :s. When the junction Southern blot hybridisation have shown that d as markers, five car-deletions or duplications of DNA containing cally diagnosed among one or more dystrophin exons are responsible wo families of DMD/ for approximately 70% of DMD/BMD s novel method allows cases.2'-0 Female carriers of rearranged dysre identification of car-trophin genes can be identified by quantitative *sforDMDIBMDwith-Southern blot analysis. However, because signal intensities of the hybridised bands must be measured accurately, results are occasionally ambiguous.1 [1][2][3][4][5][6][7][8][9][10][11][12][13] Junction fragments produced by gross alterations of the dystrophin gene are observed in 2 Materials and methods SUBJECTS We studied 27 unrelated Japanese male patients in 27 families and six female members of two of the families. Of the 27 patients, 19 with DMD and one with BMD carried partial deletions and the remaining seven DMD patients carried partial duplications in the dystrophin gene.…”