LAMA2-related muscular dystrophy (LAMA2 MD or MDC1A) is the most frequent form of congenital muscular dystrophies. It is caused by mutations in LAMA2, the gene encoding laminin-α2, one chain of the heterotrimeric extracellular matrix protein laminin-211 (α2β1γ1). Most patients lack laminin-α2 due to bi-allelic loss-of-function mutations in LAMA2. The large size of the coding sequence for laminin-α2 (~ 9.4kb) and the heterotrimeric structure of laminin-211 present a challenge for AAV-mediated gene replacement or gene editing strategies. Here, we describe the development of an AAV-based gene therapy to functionally replace laminin-211 by two small linker proteins. Prior work in transgenic mice has demonstrated that this Simultaneous Expression of Artificial Linkers (SEAL) in skeletal muscle of LAMA2 MD mice has a tremendous ameliorative effect on disease progression (Reinhard et al., 2017. Sci Transl Med. 9). As both linkers, mini-agrin (mag) and αLNNd, are small enough to be efficiently packed into AAV, we intravenously co-injected mag- and αLNNd-expressing AAV9 or AAVMYO vectors at postnatal day 1 into a LAMA2 MD mice. Both linkers were highly expressed in skeletal muscle and led to a strong improvement of disease phenotypes, including an increase in body- and muscle weights, grip strength and myofiber size and the reduction of fibrosis. Using AAVMYO as a vehicle, the same improvement was seen at a ten-fold lower dose than with AAV9. These studies thus establish that systemic delivery of AAVs expressing the two linkers (SEAL technology) might be a possible strategy to treat LAMA2 MD patients. As the linkers are designed from proteins (agrin, nidogen-1 and laminin-α1) that are all expressed in LAMA2 MD patients, this treatment is expected to be well tolerated. Moreover, the fact that the linkers are secreted and act in the extracellular matrix where they also accumulate, suggests that this treatment might be efficacious over a wide dose range of AAV9/AAVMYO.