The interstitial collagenase gene (CLG), one of the main candidates in severe generalized recessive epidermolysis bullosa dystrophica (SGREBD), is closely linked to the stromelysin-1 (STMY1) and stromelysin-2 (STMY2) genes. These three loci map on chromosome 11 (q21-q22.3), where they constitute a cluster of genes coding for metalloproteinases involved in the degradation of the extracellular matrix (ECM). A recessive form of cerebellar ataxia of post-puberal onset (CLA1) has also been assigned to chromosome 11 (q14-q21). Since useful restriction fragment length polymorphisms (RFLPs) for the CLG gene are not available, we have studied the inheritance of the marker TaqI RFLP of the STMY1 gene in a North Italian family with a child affected by SGREBD, and his two sisters showing cerebellar ataxia (CA) of post-puberal onset. We have also studied the MspI RFLP of the fibronectin gene (FN1), which is located on chromosome 2q34-q36, and which codes for non-collagenous matrix proteins. Since we did not observe the segregation of the pathological phenotypes with STMY1 and FN1 RFLPs, we excluded the involvement of these genes in both the SGREBD and CA present in this family. The exclusion of the STMY1 gene indicates that the mutation causing SGREBD cannot be located in the CLG and/or STMY2 genes because of their proximity to the STMY1 locus. These data also indicate that the CA form here reported is not attributable to alterations in regions close to the collagenase cluster on chromosome 11.

A cluster of metalloproteinase genes, stromelysin, fibroblast collagenase, and stromelysin 2 together with the anonymous DNA marker D11S385, was mapped using pulsed-field gel electrophoresis to a 135-kb region of chromosome 11q22-q23. The physical proximity of these markers was subsequently confirmed using two YAC clones, and their relative order was established as stromelysin 2-collagenase-stromelysin-D11S385. The pattern of marker representation in a panel of radiation-reduced chromosome 11 hybrids suggests that the metalloproteinase gene/D11S385 cluster is orientated with STMY2 closest to the centromere.

The gene coding for human collagenase-3 (CLG3), a recently described matrix metalloproteinase produced by breast carcinomas, has been localized by fluorescence in situ hybridization on chromosome 11q22.3. Physical mapping of an isolated YAC clone containing CLG3 has revealed that this gene is tightly linked to those encoding other matrix metalloproteinases, including fibroblast collagenase (CLG1), stromelysin-1 (STMY1), and stromelysin-2 (STMY2). Further mapping of this region using pulsed-field gel electrophoresis has shown that the CLG3 gene is localized to the telomeric side of the matrix metalloproteinase cluster, the relative order of the loci being centromere-STMY2-CLG1-STMY1-CLG3-telomere.