Transcriptional regulation differs in affected facioscapulohumeral muscular dystrophy patients compared to asymptomatic related carriers

Abstract

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive muscle disorder that has been associated with a contraction of 3.3-kb repeats on chromosome 4q35. FSHD is characterized by a wide clinical inter- and intrafamilial variability, ranging from wheelchair-bound patients to asymptomatic carriers. Our study is unique in comparing the gene expression profiles from related affected, asymptomatic carrier, and control individuals. Our results suggest that the expression of genes on chromosome 4q is altered in affected and asymptomatic individuals. Remarkably, the changes seen in asymptomatic samples are largely in products of genes encoding several chemokines, whereas the changes seen in affected samples are largely in genes governing the synthesis of GPI-linked proteins and histone acetylation. Besides this, the affected patient and related asymptomatic carrier share the 4qA161 haplotype. Thus, these polymorphisms by themselves do not explain the pathogenicity of the contracted allele. Interestingly, our results also suggest that the miRNAs might mediate the regulatory network in FSHD. Together, our results support the previous evidence that FSHD may be caused by transcriptional dysregulation of multiple genes, in cis and in trans, and suggest some factors potentially important for FSHD pathogenesis. The study of the gene expression profiles from asymptomatic carriers and related affected patients is a unique approach to try to enhance our understanding of the missing link between the contraction in D4Z4 repeats and muscle disease, while minimizing the effects of differences resulting from genetic background.

Fig. 1.

Validation of the expression of the chemokines through RT-PCR. The expression levels of CXCL9, CXCL10, and CXCL11 were calculated relative to the mean value from normal controls in the function of residual number of D4Z4. (A) In affected patients, the rank correlations are 1.000* (CXCL9), 1.000* (CXCL10), and 0.800*** (CXCL11); while the line correlations are 0.933** (CXCL9), 0.730*** (CXCL10), and 0.805*** (CXCL11). (B) In asymptomatic carriers, the rank correlations are –0,464*** (CXCL9), –0.564*** (CXCL10), and –0.527*** (CXCL11); while the line correlations are –0.595*** (CXCL9), –0,004*** (CXCL10), and –0.191*** (CXCL11). *, P < 0.0001; **, P = 0.07; ***, P > 0.1.

Fig. 2.

Relative expression of the other genes validated through RT-PCR in function of the number of D4Z4 repeats. The calculated correlation coefficients for the expression level and the number of repeats for STATH (A) in affected patients are 0.8000*** (rank) and 0.2645***(line) and in asymptomatic carriers are –0.7537** (rank) and –0.4417***(line); for LOC91431 (B) in affected patients are 0.2000*** (rank) and 0.6908*** (line) and in asymptomatic carriers are –0.8208** (rank) and –0.8280** (line); for LPP (C) in affected patients are 1.000* (rank) and 0.7503*** (line) and in asymptomatic carriers are –0.6669*** (rank) and –0.7650*** (line); for PRIC285 (D) in affected patients are 0.2000*** (rank) and –0.1361*** (line) and in asymptomatic carriers are 0.5643*** (rank) and 0.4008*** (line). *, P < 0.0001; **, P = 0.08; ***, P > 0.1.