Usefulness of a CACA repeat polymorphism in genotype assignments in Duchenne/Becker muscular dystrophy

Molecular diagnosis of dystrophinopathies using a multi-technique analysis algorithm

INTRODUCTION

Dystrophinopathies are X-linked recessive neuromuscular diseases caused by mutations in the dystrophin gene. In this study we aimed to detect mutations within the dystrophin gene in DMD patients, to determine the carrier status of women, and to perform a prenatal diagnosis.

METHODS

We analyzed 17 individuals from 2 unrelated families with a history of DMD. We used multiplex PCR, multiplex ligation-dependent probe amplification (MLPA), and short tandem-repeat (STR) segregation analysis to accurately detect and characterize the mutations and to identify the at-risk haplotype.

RESULTS

The selected methodology allowed for characterization of 2 single-exon out-of-frame deletions in affected patients. Nine of 13 women and a fetus were excluded from being carriers. Three recombination events were found and suggested that germline mosaicism had occurred in both families.

CONCLUSIONS

This methodology proved to be efficient for characterizing the disease-causing mutation in affected individuals and for assessing the carrier status in healthy relatives. These findings helped inform precise genetic counseling and contributed to characterization of the disease in the Argentine population.

Detection of germline mosaicism in two Duchenne muscular dystrophy families using polymorphic dinucleotide (CA)n repeat loci within the dystrophin gene

BACKGROUND

Approximately one-third of new cases of Duchenne muscular dystrophy (DMD) can be attributed to sporadically arising new mutations, however in the majority of cases the DMD mutation has been inherited from the mother. These female carriers can have either a constitutive or mosaic mutation.

AIM

The aim of this study was to determine the segregation of the at-risk haplotype and to find a deletion in the dystrophin gene of patients.

METHOD

We analyzed individuals from two families with a history of DMD in order to predict the carrier status of related females. In one of these cases the mother had two affected sons, while in the other one son and two grandchildren were affected; therefore we predict that the mother would be an obligatory carrier.

RESULTS

Haplotype analysis of the DMD loci revealed that in the two families both the healthy and affected brothers had inherited the same X maternal chromosome. However, the affected brother carried a deletion, which was absent in the unaffected sibling.

CONCLUSION

These findings suggested that the mothers in the two families were germline mosaics for the DMD gene. The results of this study demonstrate the usefulness of the methodology that combine the haplotype analysis with the identification of the mutation in order to detect hidden germline mosaicisms and, thus, improve genetic counseling.

Direct deletion analysis in two Duchenne muscular dystrophy symptomatic females using polymorphic dinucleotide (CA)n loci within the dystrophin gene

Duchenne muscular dystrophy (DMD) is the most common hereditary neuromuscular disease. It is inherited as an X-linked recessive trait in which males show clinical manifestations. In some rare cases, the disease can also be manifested in females. The aim of the present study was to determine the molecular alteration in two cases of nonrelated DMD symptomatic carriers with no previous history of DMD. Multiplex PCR is commonly used to search for deletion in the DMD gene of affected males. This method could not be used in females because the normal X chromosome masks the deletion of the mutated one. Therefore, we used a set of seven highly polymorphic dinucleotide (CA)(n) repeat markers that lie within the human dystrophin gene. The deletions were evidenced by hemizygosity of the loci under study. We localized a deletion in the locus 7A (intron 7) on the maternal X chromosome in one case, and a deletion in the region of introns 49 and 50 on the paternal X chromosome in the other. The use of microsatellite genotyping within the DMD gene enables the detection of the mutant allele in female carriers. It is also a useful method to provide DMD families with more accurate genetic counseling.

Carrier detection in Duchenne and Becker muscular dystrophy Argentine families

In order to offer carrier detection, genetic counseling, and prenatal diagnosis to families with Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) in our country, segregation analysis of highly polymorphic short tandem repeats (STR) (dC-dA)n: (dG-dT)n loci was utilized. The risks to females of 15 DMD BMD families (9 familial and 6 sporadic) were evaluated on STR, pedigree and serum creatine kinase (SCK) data. From the 36 females at risk of being carriers (not including 8 obligate carriers), results of STR analysis were compatible with carrier status in 7 and not compatible in 20. In 9 females, no information regarding carriership was derived from the STR analysis. Prenatal diagnosis is now possible on the carrier females. Previously identified deletions in the central part of the gene were confirmed by STR analysis in 3 families. Five new alleles were identified in Argentine individuals; allele frequencies differed from those of North American people. Results derived from this study are useful for carrier detection and genetic counseling in DMD/BMD. One case of probable mosaicism in an unaffected father was detected on a pedigree basis in a family with DMD patients.