Tackling fibrosis and inflammation in LAMA2-RD by in vivo modulation of a novel modifier gene

ongoing

Merosin-deficient congenital muscular dystrophy (LAMA2-RD) is caused by mutations in the LAMA2 gene, coding for the α2 subunit of laminin-211 (merosin). Typically, LAMA2-RD patients with absent merosin are clinically severe and unable to walk, while those producing a partially functional merosin are clinically milder. I identified a unique family in which the oldest of two affected siblings shows a novel and extremely mild phenotype despite the complete lack of merosin. This patient is still ambulant at 33 years with no respiratory insufficiency or cardiomyopathy. Notably, this patient carries the same LAMA2 loss-of-function mutation as the sibling who followed the typical severe disease course. Hypothesizing that genetic modifier(s) in the atypical patient mitigate the consequences of complete merosin deficiency via a novel mechanism, I isolated unique ultra-rare polymorphisms in genetic factors related to genes expressed in the atypical patient muscle but not in muscle of non-related LAMA2-RD patients, and I identified a novel candidate modifier controlling both fibrosis and inflammation (key drivers of LAMA2-RD pathogenesis). Given that this modifier is severely upregulated in the control LAMA2-RD patients but highly downregulated in the atypical patient, I will decrease its expression in the severely affected LAMA2-RD mouse model DyW/DyW by using the CRISPR-interference tool delivered by a single AAV9. I will then assess motor strength and endurance in treated mice. Finally, I will isolate highly affected muscles and sciatic nerve to characterize any molecular and morphological change occurring in these tissues upon modulating the modifier gene expression. I expect to observe functional improvement in LAMA2-RD animals, thus ameliorating their phenotype. The proposed project will elucidate novel mechanisms attenuating LAMA2-RD severity and will allow me to design new therapeutic approaches for this disorder for which, to date, there is no approved treatment.