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Do NGS-based techniques represent a first-line testing in suspected Duchenne muscular dystrophy?

#apaperaday: Do NGS-based techniques represent a first-line testing in suspected Duchenne muscular dystrophy?

In today’s #apaperaday, Prof. Aartsma-Rus reads and comments on the paper titled: Do NGS-based techniques represent a first-line testing in suspected Duchenne muscular dystrophy?

Today’s pick is from the journal clinical case reports by Hosseini et al on using next generation sequencing to find a mutation in the dystrophin gene for a patient suspected of having Duchenne. Group from Iran. Doi 10.1002/ccr3.5916.

Duchenne and Becker are both caused by mutations in the dystrophin gene. Duchenne is the more severe type, caused by frame-shifting mutations, while Becker is less severe and caused by mutations that maintain the reading frame & allow production of partially functional dystrophin.

Mutations in dystrophin are one of the most common causes of inherited muscle diseases. It is important to find the mutation as that allows carrier analysis, family planning, but also initiation of multidisciplinary care.

As deletions & duplications of >1 exons are common, step 1 of genetic analysis is an MLPA test that detects the presence & abundance of each of the 79 exons. When no deletions or duplications are found, Sanger sequencing is used to find small mutations (present in ~25%)

Here authors present the case of an 8 year old boy with muscle weakness. IQ is normal. CK is elevated (13k U/L). There was a history of muscular dystrophy in his uncle and male cousin. This was all suggestive for a dystrophin mutation.

Authors first performed MLPA but did not find a deletion. They then performed NGS rather than sanger sequencing, as a quicker approach to find small mutations. They did capture the dystrophin genes to enrich sequencing for this gene due to the expected mutation in this gene.

NGS identified a duplication of exon 10-42. Authors then confirmed this duplication by looking in the MLPA data. Ideally they would have picked it up in the initial analysis, but with large duplications this might be more challenging.

Authors discuss the importance of finding a genetic mutation – fully agree with this. However, there are several additional comments I would like to make 

  1. This duplication is in frame, so one might expect Becker rather than Duchenne. Authors do not discuss this. Duplication mutations are notorious for not following the reading frame rule. However authors do not provide sufficient information to see whether this is Duchenne, Becker or intermediate. When did the symptoms start? For this case and his uncle and cousin?
  1. It is very likely that in the future NGS will be a one step way to find mutations for most Duchenne once it becomes cheaper to do this than the two step MLPA –> Sanger approach used now. Then it is really important to involve experienced people to interpret the results.

This case here is a showcase. The authors do not seem to realize the mutation is in-frame. Also they did not check properly for a duplication in the MLPA. This is not a sneer towards the authors, but just underlines how important it is to have experts involved. Kudos to the authors for sharing the work so people can learn.