Lee et al. (2003) did not show any variation between non-traumatic ON patients and controls. In Perthes' disease, reduced plasminogen was reported by Pósán et al. (2003), but normal levels were reported by Koo et al. (2002). These discordant results may depend on ethnic differences, as hypothesized by Lee et al. (2003). This evidence concerns the gene PLG and glycogen storage disease VI.