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

Cardiac Involvement in Dystrophin-Deficient Females: Current Understanding and Implications for the Treatment of Dystrophinopathies

Duchenne muscular dystrophy (DMD) is a fatal X-linked recessive condition caused primarily by out-of-frame mutations in the dystrophin gene. In males, DMD presents with progressive body-wide muscle deterioration, culminating in death as a result of cardiac or respiratory failure. A milder form of DMD exists, called Becker muscular dystrophy (BMD), which is typically caused by in-frame dystrophin gene mutations. It should be emphasized that DMD and BMD are not exclusive to males, as some female dystrophin mutation carriers do present with similar symptoms, generally at reduced levels of severity. Cardiac involvement in particular is a pressing concern among manifesting females, as it may develop into serious heart failure or could predispose them to certain risks during pregnancy or daily life activities. It is known that about 8% of carriers present with dilated cardiomyopathy, though it may vary from 0% to 16.7%, depending on if the carrier is classified as having DMD or BMD. Understanding the genetic and molecular mechanisms underlying cardiac manifestations in dystrophin-deficient females is therefore of critical importance. In this article, we review available information from the literature on this subject, as well as discuss the implications of female carrier studies on the development of therapies aiming to increase dystrophin levels in the heart.

Molecular diagnosis of dystrophinopathies in Morocco and report of six novel mutations

Dystrophinopathies are the most common genetic neuromuscular disorders during childhood, with an X-linked recessive inheritance pattern. Because of clinical and genetic heterogeneity of dystrophinopathies, genetic testing of dystrophin gene at Xp21.2 is constantly evolving. Multiplex Polymerase Chain Reaction (MPCR) is used in the first line to detect common exon deletions of dystrophin gene (accounting for 65% of mutations), followed by the Multiplex Ligation-dependent Probe Amplification (MLPA) technique to reveal deletions of exons outside the usual hotspot and duplications in male and female carriers. (MLPA adds another 10-15% positive cases to MPCR). Recently, Next Generation Sequencing allows to screen for rare large and point mutations. We report here, molecular analysis results of dystrophin gene during 27 years in a large Moroccan cohort of 356 patients, using the multiplex polymerase chain reaction (MPCR) to screen for hot-spot exon deletions. First applications of whole dystrophin gene sequencing in our lab lead to the identification of six novel mutations.

Molecular Analysis-Based Genetic Characterization of a Cohort of Patients with Duchenne and Becker Muscular Dystrophy in Eastern China

Background:

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are common X-linked recessive neuromuscular disorders caused by mutations in dystrophin gene. Multiplex polymerase chain reaction (multiplex PCR) and multiplex ligation-dependent probe amplification (MLPA) are the most common methods for detecting dystrophin gene mutations. This study aimed to contrast the two methods and discern the genetic characterization of patients with DMD/BMD in Eastern China.

Methods:

We collected 121 probands, 64 mothers of probands, and 15 fetuses in our study. The dystrophin gene was detected by multiplex PCR primarily in 28 probands, and MLPA was used in multiplex PCR-negative cases subsequently. The dystrophin gene of the remaining 93 probands and 62 female potential carriers was tested by MLPA directly. In fetuses, multiplex PCR and MLPA were performed on 4 fetuses and 10 fetuses, respectively. In addition, sequencing was also performed in 4 probands with negative MLPA.

Results:

We found that 61.98% of the subjects had genetic mutations including deletions (50.41%) and duplications (11.57%). There were 43.75% of mothers as carriers of the mutation. In 15 fetuses, 2 out of 7 male fetuses were found to be unhealthy and 2 out of 8 female fetuses were found to be carriers. Exons 3–26 and 45–52 have the maximum frequency in mutation regions. In the frequency of exons individually, exon 47 and exon 50 were the most common in deleted regions and exons 5, 6, and 7 were found most frequently in duplicated regions.

Conclusions:

MLPA has better productivity and sensitivity than multiplex PCR. Prenatal diagnosis should be applied in DMD high-risk fetuses to reduce the disease incidence. Furthermore, it is the responsibility of physicians to inform female carriers the importance of prenatal diagnosis.

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.

Screening for conditions that do not meet the Wilson and Jungner criteria: the case of Duchenne muscular dystrophy

In this manuscript, I examine four overlapping policy and ethical issues regarding screening newborns (and infants) for Duchenne muscular dystrophy (DMD). First, what are the risks and benefits of expanding newborn screening (NBS) to include DMD? Second, if NBS were to expand to include DMD, should it require informed consent? Third, should NBS for DMD be limited to boys? Why or why not? Fourth, when is the ideal timing for screening (prenatal, newborn, or later in infancy) and what factors influence this determination? I argue that decisions about when, how, and whom to test reflect a tension between maximizing uptake and diagnosis versus maximizing autonomy and choice with respect to genetic information. I conclude that screening for DMD is a valid moral option, but not as part of the mandatory NBS population program. Rather, I propose that screening for DMD should be offered only on a voluntary basis beyond the newborn period. I support offering this screening to families of young boys and girls to ensure that all children and their families can benefit from early diagnosis and its reproductive implications. A rigorous consent process will be necessary to ensure that the decision whether or not to test is a voluntary and informed choice.

Identify female carriers and de novo mutations in deletional Duchenne/Becker muscular dystrophy families

By using multiple polymerase reaction (mPCR) and haploid analysis of 11 short tandem repeats (STRs) in dystrophin gene locus to identify female carriers in deletional DMD/BMD (Duchenne/Becker Muscular Dystrophy) families, valuable information can be gathered for prenatal diagnosis. In this article, de novo mutations were detected in two out of the four patients, and one of the four female members was identified as an obligate DMD gene carrier based on the haplotype analysis. Multiple PCR and STRs haploid linkage analysis are rapid, accurate, objective methods to identify female member status, and well suited for routine use in clinical laboratories engaged in DMD/BMD research for counseling, gene diagnosis and prenatal diagnosis. During mPCR analysis, the amplicon of exon 45 showed different electrophoresis mobility in different kinds of gels. Polyacrylamide Gels Electrophoresis (PAGE) was accurate and rapid for analyzing the products of mPCR, but the mobility of different amplicons need to be considered in data analysis.