Genetic and clinical modifiers in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a neuromuscular disease caused by out-of-frame mutations in the DMD gene resulting in the lack of dystrophin in skeletal muscle fibres. Even though all DMD patients share the same molecular defect, it is possible to observe high variability in the disease's progression, i.e. differences in loss of ambulation age, onset of respiratory and cardiac failure. This variability is due both to environmental and genetic factors. Genetic factors may be divided in cis-acting, nominally the type of DMD mutation, and trans-acting, or modifier SNPs. These are polymorphisms in genes, different from the causative DMD, that have and effect on the phenotype. There are several modifier SNPs known to alter age at loss of ambulation. These are: rs28359074 in SPP1, rs2303729, rs1131620, rs1051303 e rs10880 in LTBP4, rs1883832 e rs6074022 in CD40, rs1815739 in ACTN3, rs2725797 e rs2624259 in THBS1. The main goal of my PhD was the study of clinical and genetic variability in DMD, through in vitro and observational retrospective studies. We carried an in vitro research to verify the interaction of rs28357094 in SPP1, that codifies for osteopontin (OPN), and glucocorticoids treatment (Deflazacort) in primary myoblasts and myotubes derived from healthy individuals and DMD patients. We found that OPN is overexpressed in rs28357094 TG genotype myotubes, compare to TT genotype. Moreover, deflazacort treatment induces an increase in OPN production in TG myotubes. These results confirmed the interaction between rs28357094 and glucocorticoids treatment. Afterwards, we studied the effect of the known modifiers, on multiple phenotypic aspects: upper limbs performance, respiratory and cardiac function. These analyses had been made possible thanks to the collaboration in the data collection phase of several Italian centres. Our goals were to find new potential therapeutic targets and to provide information useful for patients stratification in clinical trials. We were able to confirm the effect of some SNPs, known to be modifier of age at loss of ambulation, on diverse outcomes measures as performance of upper limbs, respiratory and cardiac function. Furthermore, we assess the protective effect of glucocorticoids treatments on diseases aspects other than ambulation, and provide new information about the correlation between DMD mutations and phenotype severity. Finally, I switched my interest to three-dimensional modelling of neuromuscular diseases, aiming to clarify pathological mechanisms and provide a versatile platform for drug screening and test.