In Ullrich congenital muscular dystrophy, due to heterozygous mutations in COL6 genes, collagen VI is preserved in the interstitium but lost in the sarcolemma. We found that the binding ability of mutated collagen VI to extracellular matrix was markedly reduced compared to control. This indicates that heterozygous mutations in COL6 genes diminish the anchorage of collagen VI microfibrils to the extracellular matrix surrounding myocytes. This is the cause for sarcolemma-specific collagen VI deficiency.