This paper reports a study of the serum
somatomedin activity in 67 boys with
Perthes' disease and in 43 control boys aged three to 11 years. It was undertaken to evaluate some abnormalities of growth in children with
Perthes' disease that have been previously reported. A brief account is given of knowledge relating to
somatomedins in postnatal and fetal life. Serum
somatomedin activity was measured using a bioassay based on the principle that
somatomedins stimulate the synthesis of both
DNA and
proteoglycans in porcine costal cartilage. In control boys, the serum
somatomedin activity increased with age, which is consistent with previous reports for normal children. In affected boys, the normal increase in serum
somatomedin activity with age did not occur. The
somatomedin activity in affected boys is higher than in control boys at three to five years but not at six to 11 years of age. Findings support the hypothesis that some children with
Perthes' disease have an abnormality of the
growth hormone-dependent
somatomedins. The serum findings together with those of both skeletal age delay and impaired skeletal growth distally in the limbs are consistent with the view that the general disorder of some children with
Perthes' disease results from an imbalance in mechanisms that determine the postnatal transition from the "fetal" to the "basic" component of the normal human growth curve.