Background: Recessive dystrophic epidermolysis bullosa (RDEB) is a severe genetic skin blistering disorder caused by mutations in the gene COL7A1 encoding type VII collagen. Most of the patients' clinical severity depends in part on the nature and location of the mutations, ranging from the mild form described as RDEBother-generalized (RDEB-O) to the more aggressive phenotype described as RDEBsevere-generalized (RDEB-sev gen). However, interfamilial and interindividual differences in subjects with identical COL7A1 mutations suggest the presence of modifier elements, which may influence severity. There is a single nucleotide polymorphism (SNP) at the promoter of the MMP1 gene-encoding matrix metalloproteinase type 1, which has been studied as a genetic disease modifier in different patient cohorts with different findings. Methods: We tested the SNP in 30 patients with RDEB and 130 controls whose four grandparents were born in northeastern Mexico. Patients were clinically classified as RDEB-sev gen and RDEB-O by three dermatologists. The SNPStats, RXC, and SPSS software were used to perform statistical testing. Results: The allele frequencies for 2G were 0.607, 0.562, and 0.642 for RDEB-O, RDEB-sev gen, and the control group, respectively. When the genotype frequencies were compared, there was no significant difference between RDEB-sev gen (OR = 0.38, CI 95% 0.12-1.21), RDEB-O (OR = 1.03, CI 95% 0.21-4.96), and the control group. Conclusion: We found no significant association in relation to the severity of the study subjects and the SNP at the promoter of the MMP1 gene. © 2014 The International Society of Dermatology.