COL6A1 and Ullrich congenital muscular dystrophy: Furthermore, the intracellular accumulation of the α3 chain in Col6a1 null fibroblasts correlates with the increased intracellular collagen VI labelling that was seen in cultures from UCMD patients [5] and the accumulation of the α1 chain in collagen VI α3 chain mutant mouse fibroblasts [33], indicating that synthesis of individual collagen VI chains is independent.