In November 1994, Ralph Brinster and coworkers published two papers that should be regarded as the start of a paradigm shift in reproductive biology. The authors reported on the successful transplantation of germ cells to sterile mouse testes. The donor cells not only survived and proliferated in the recipient testes but they also entered the long and complex process of spermatogenesis, and differentiated into fully functional spermatozoa able to fertilize eggs and give rise to normal offspring (1, 2). The potentials of these novel discoveries were clearly evident to Martin Dym as expressed by his commentary in the same issue of the Proceedings of the National Academy of Sciences of the USA where the original papers were published (3). More recently, these initial findings in the mouse have been partially reproduced in a rat model using a somewhat different technical approach for the transplantation (4). This year, Brinster and coworkers
Rikke Beck Jensen, Ajay Thankamony, Susan M O'Connell, Jeremy Kirk, Malcolm Donaldson, Sten-A Ivarsson, Olle Söder, Edna Roche, Hilary Hoey, David B Dunger and Anders Juul
Short children born small for gestational age (SGA) are treated with a GH dose based on body size, but treatment may lead to high levels of IGF1. The objective was to evaluate IGF1 titration of GH dose in contrast to current dosing strategies.
In the North European Small-for-Gestational-Age Study (NESGAS), 92 short pre-pubertal children born SGA were randomised after 1 year of high-dose GH treatment (67 μg/kg per day) to three different regimens: high dose (67 μg/kg per day), low dose (35 μg/kg per day) or IGF1 titration.
The average dose during the second year of the randomised trial did not differ between the IGF1 titration group (38 μg/kg per day, s.d. 0.019) and the low-dose group (35 μg/kg per day, s.d. 0.002; P=0.46), but there was a wide variation in the IGF1 titration group (range 10–80 μg/kg per day). The IGF1 titration group had significantly lower height gain (0.17 SDS, s.d. 0.18) during the second year of the randomised trial compared with the high-dose group (0.46 SDS, s.d. 0.25), but not significantly lower than the low-dose group (0.23 SDS, s.d. 0.15; P=0.17). The IGF1 titration group had lower IGF1 levels after 2 years of the trial (mean 1.16, s.d. 1.24) compared with both the low-dose (mean 1.76, s.d. 1.48) and the high-dose (mean 2.97, s.d. 1.63) groups.
IGF1 titration of GH dose in SGA children proved less effective than current dosing strategies. IGF1 titration resulted in physiological IGF1 levels with a wide range of GH dose and a poorer growth response, which indicates the role of IGF1 resistance and highlights the heterogeneity of short SGA children.