Nonsense-mediated mRNA decay (NMD) is an mRNA quality-control mechanism that degrades aberrant mRNAs containing premature translation termination codons (PTCs). The essential proteins for NMD include SMG-1, a protein kinase, and Upf1, a substrate of SMG-1 with RNA helicase activity. In this study, we evaluated the effects of NMD inhibition by siRNA-mediated knockdown of SMG-1 or Upf1 on the phenotype of Ullrich disease, an autosomal recessive congenital muscular dystrophy. The patient studied showed a homozygous frameshift mutation with a PTC in the collagen VI alpha2 gene, which encodes a truncated but partially functional protein. The patient's fibroblasts showed a nearly complete loss of the triple-helical collagen VI protein and functional defects in the extracellular matrix (ECM) due to the crucial deficiency of the collagen VI alpha2 protein. We have shown that siRNA-mediated knockdown of SMG-1 or Upf1 causes the up-regulation of the mutant triple-helical collagen VI, resulting in the formation of partially functional ECM. We suggest that the inhibition of NMD may be useful as a therapeutic approach to treat some human genetic diseases exacerbated by NMD.