Basal laminae (basement membranes) are flexible thin sheets of specialized extracellular matrix separating organ cells from the underlying or surrounding connective tissues. They are found beneath epithelial and endothelial cells amd surrounding different cells, such as muscle fibers and nerves. Basal laminae are mainly composed of type IV collagen laminin, heparan sulfate proteoglycan, and nidogen that are specific for these structures. These proteins are not only important for forming the structural substrate for the cells positioned on the of basal laminae, but also have several other biological functions. For example, they promote cell differentiation and adhesion, serve as a specific highway for cell migration, determine cell polarity, and are involved in regeneration processes as well as in the filtration of body fluids. In addition, changes in the basal laminae can lead to numerous acquired and genetic diseases. To facilitate studies on basal laminae and, particularly, their involvement in diseases such as Alport syndrome, leiomyomatosis, and also their possible role in congenital muscular dystrophy, the complete exon intron structure of the gene for the human type IV collagen a6 chain (COL4A6) and laminin a2 chain (LAMA2) were determined. The COL4A6 was shown to span about 425 Kb and contain 46 exons, of which exon IB was found to be alternatively used (1). The COL4A6 characterized in this study is the largest collagen to be analyzed thus far. The large size of COL4A6 is mainly contributed to by a single 340 Kb second intron, while the sizes of other introns only range between 0.164 and 16 kb. Based on the exon-intron structure of COL4A6, the possible involvement of this gene in patients with Alport syndrome was investigated. Sequencing of four exons (exons 2, 12, 13, and 14) in 250 patients with Alport syndrome revealed no mutations, showing that mutations in the a6(1V) collagen chain gene are not likely to cause Alport syndrome (II). In contrast, 17 different mutations were found in the same study in ...