Gene Expression in Slipped Capital Femoral Epiphysis

Background: Slipped capital femoral epiphysis is a poorly understood condition affecting adolescents. Prior studies have suggested that the etiology may be related to abnormal collagen in the growth plate cartilage, but we are not aware of any investigations analyzing collagen or other structural proteins on a molecular level in the affected tissue. This study was performed to evaluate expression of mRNA for key structural molecules in growth plate chondrocytes of patients with slipped capital femoral epiphysis. Methods: A core biopsy of the proximal femoral physis was performed in nine patients with slipped capital femoral epiphysis, and the specimens were compared with five specimens from the normal distal femoral and proximal tibial and fibular physes of age-matched patients treated surgically for a limb-length inequality. We utilized laser capture microdissection techniques followed by quantitative reverse transcription-polymerase chain reaction analysis to determine if a change or abnormality in type-II-collagen and/or aggrecan gene expression may be associated with slipped capital femoral epiphysis. With these techniques, we correlated chondrocyte spatial location and gene expression to provide greater insight into this pathological condition and a more complete understanding of growth plate biology in general. Results: Downregulation of both type-II collagen and aggrecan was found in the growth plates of the subjects with slipped capital femoral epiphysis when compared with the levels in the age-matched controls. In eight specimens from affected patients, the level of expression of type-II-collagen mRNA was, on the average (and standard error of the mean), 13.7% ± 0.2% of that in four control specimens and the aggrecan level averaged only 26% ± 0.2% of the control aggrecan level. Conclusions: The decreases that we identified in type-II-collagen and aggrecan expression would affect the quantity, distribution, and organization of both components in a growth plate, but these changes could be associated with either the cause or the result of a slipped capital femoral epiphysis. Clinical Relevance: With further study with use of laser capture microdissection and quantitative reverse transcription-polymerase chain reaction, as well as other molecular biological approaches, these observations may be found to lead to a more complete understanding, and be pertinent to the treatment and possible prevention, of this serious adolescent disorder.