A series of unfortunate events: familial case of DMD, two different mutational events and skewed X chromosome inactivation in a pregnant woman

LUCE L; CARCIONE M; MAZZANTI; SZIJAN I; MENAZZI; FRANCIPANE; NEVADO J; LAPUNZINA; ROSSETTI L; RADIC CP; ABELLEYRO, M.M.; DE BRASI C; GILIBERTO F

Congreso; International Annual Congress of the World Muscle Society (WMS); 2019

Duchenne muscular dystrophy (DMD) is a neuromuscular X-linkedrecessive disease caused by mutations in DMD gene. Here, we presenta family with a DMD symptomatic pregnant woman and two affectedboys. One of them had a previous multiplex PCR study showing a45-54 exon deletion. Interestingly, during the prenatal diagnosis anothermutation was discovered in the pregnant woman and her fetus, a 38-43 exon duplication. On the basis of this finding, we reanalyzed theinitially studied boy, discovering both mutations in his gDNA. In order tounravel this riddle, we performed a complete molecular analysis in familymembers, applying the following techniques: MLPA, STRs segregation,Humara Assay, CGH Array, Sanger sequencing and WGS. As expected,the Humara assay revealed that the symptomatic female has skewed Xchromosome Inactivation (XCI), while an asymptomatic carrier showed arandom XCI. Given the inheritance pattern of the rearrangements, onlythe affected child carried the del/dup, we could deduce that the deletionwas the second mutational event. Furthermore, STRs segregation allowedthe detection of a recombinant event in the affected boy, which could berelated to the generation of the deletion. We were able to characterize thedeletion breakpoints NC_000023.10:g.31664475_32111223del, suggestingthe involvement of the non-homologous end joining mechanism. On theother hand, we limited the borders of the duplication up to NC_000023.10:g.(32245444_32247193)_(32380996_32385390)dup by CGH array. However,a thorough characterization of the duplication is currently being done. Theprofound analysis of complex structural variants, such as the presented one,would allow to detect predisposing mutagenic sequences and widen theunderstanding on the molecular events that takes place in DMD gene. Finally,this study highlights the importance of retesting patients with identifieddeletions by PCR, in order to reduce the probability of missing out otherrearrangements which could affect the effectiveness of mutation-dependenttherapies.