Open Access Highly Accessed Research article

Genetic characterization in symptomatic female DMD carriers: lack of relationship between X-inactivation, transcriptional DMD allele balancing and phenotype

Simona Brioschi1, Francesca Gualandi1, Chiara Scotton1, Annarita Armaroli1, Matteo Bovolenta1, Maria S Falzarano1, Patrizia Sabatelli2, Rita Selvatici1, Adele D’Amico3, Marika Pane4, Giulia Ricci5, Gabriele Siciliano5, Silvana Tedeschi6, Antonella Pini7, Liliana Vercelli8, Domenico De Grandis9, Eugenio Mercuri4, Enrico Bertini3, Luciano Merlini12, Tiziana Mongini8 and Alessandra Ferlini1*

Author Affiliations

1 Section of Medical Genetics, Department of Experimental and Diagnostic Medicine, University of Ferrara, Ferrara, Italy

2 Istituto Di Genetica Molecolare-CNR, Istituto Ortopedico Rizzoli, Bologna, Italy

3 Department of Laboratory Medicine, Unit of Molecular Medicine, Bambino Gesù Hospital, Rome, Italy

4 Department of Child Neurology and Psychiatry, Catholic University, Rome, Italy

5 Department of Neuroscience, Neurological Clinic, University of Pisa, Pisa, Italy

6 Laboratory of Medical Genetics, I.R.C.C.S. Foundation Ca’ Granda, Maggiore Hospital, Policlinico, Milan, Italy

7 Child Neurology and Psychiatry Unit, Maggiore Hospital, Bologna, Italy

8 Neuromuscular Center, S.G. Battista Hospital, University of Turin, Turin, Italy

9 Division of Neurology, Department of Neuroscience, Civile Hospital Santa Maria della Misericordia, Rovigo, Italy

For all author emails, please log on.

BMC Medical Genetics 2012, 13:73  doi:10.1186/1471-2350-13-73

Published: 16 August 2012

Abstract

Background

Although Duchenne and Becker muscular dystrophies, X-linked recessive myopathies, predominantly affect males, a clinically significant proportion of females manifesting symptoms have also been reported. They represent an heterogeneous group characterized by variable degrees of muscle weakness and/or cardiac involvement. Though preferential inactivation of the normal X chromosome has long been considered the principal mechanism behind disease manifestation in these females, supporting evidence is controversial.

Methods

Eighteen females showing a mosaic pattern of dystrophin expression on muscle biopsy were recruited and classified as symptomatic (7) or asymptomatic (11), based on the presence or absence of muscle weakness. The causative DMD gene mutations were identified in all cases, and the X-inactivation pattern was assessed in muscle DNA. Transcriptional analysis in muscles was performed in all females, and relative quantification of wild-type and mutated transcripts was also performed in 9 carriers. Dystrophin protein was quantified by immunoblotting in 2 females.

Results

The study highlighted a lack of relationship between dystrophic phenotype and X-inactivation pattern in females; skewed X-inactivation was found in 2 out of 6 symptomatic carriers and in 5 out of 11 asymptomatic carriers. All females were characterized by biallelic transcription, but no association was found between X-inactivation pattern and allele transcriptional balancing. Either a prevalence of wild-type transcript or equal proportions of wild-type and mutated RNAs was observed in both symptomatic and asymptomatic females. Moreover, very similar levels of total and wild-type transcripts were identified in the two groups of carriers.

Conclusions

This is the first study deeply exploring the DMD transcriptional behaviour in a cohort of female carriers. Notably, no relationship between X-inactivation pattern and transcriptional behaviour of DMD gene was observed, suggesting that the two mechanisms are regulated independently. Moreover, neither the total DMD transcript level, nor the relative proportion of the wild-type transcript do correlate with the symptomatic phenotype.

Keywords:
Dystrophinopathy; Female carriers; X-inactivation; Transcriptional balancing