Study design: Report of a high dysplastic developmental spondylolisthesis in two identical twins of two unrelated families.
Objective: To investigate the multifactorial etiology of developmental spondylolisthesis.
Summary of background data: Multiple studies have suggested an association between a high pelvic incidence and the presence of isthmic spondylolisthesis. Other studies suggest a genetic background for spondylolysis and a pattern of inheritance of susceptibility to spondylolysis and spondylolisthesis. Heterozygous cartilage-derived morphogenetic protein-1 (CDMP-1) mutation has previously been associated with spondylolysis and severe spondylolisthesis.
Methods: Two identical female twins presented with a developmental spondylolisthesis. Pelvic parameters, lumbar lordosis and grade of spondylolisthesis were calculated on a lateral standing spine radiograph. MRI is performed to confirm a high dysplastic developmental spondylolisthesis. Blood sample of these four individuals were analyzed for the presence of a CDMP-1 mutation, a cartilage-specific member of the TGF-b superfamily of secreted signaling molecules that plays a key role in chondrogenesis, growth, and patterning of the developing vertebrate skeleton.
Results: PI, SS, PT, LL, and SI are significantly greater in all of these patients in comparison with the general population. Spinal MRI confirms a high dysplastic developmental spondylolisthesis in both twins. Mutation analysis of the two coding exons of CDMP-1 did not reveal any mutation in all four individuals.
Conclusion: To our knowledge, this is the first report of a high dysplastic developmental spondylolisthesis in identical twins. The presence of a high dysplastic developmental spondylolisthesis in two identical twins shows the convergence in etiology of different factors such as genetics, maturation, critical age, female sex, high pelvic incidence. Although we cannot confirm that CDMP-1 mutation plays a key role in the etiology of spondylolysis/spondylolisthesis, neither can we rule out that CDMP-1 problems may be an etiology for at least a subpopulation of patients. However, the presence of a developmental spondylolisthesis in two sets of identical twins still suggests a genetic susceptibility to spondylolysis and spondylolisthesis.