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IGF bioactivity during GH therapy varies widely in Prader-Willi syndrome
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Growth hormone dosing in children with Prader-Willi syndrome may be appropriately indicated by immunoreactive insulin-like growth factor I, according to recent study findings published in The Journal of Clinical Endocrinology & Metabolism.
“We hypothesized that GH-treated children with [Prader-Willi syndrome] have a normal IGF bioactivity, despite the high serum immunoreactive IGF-I levels,” the researchers wrote.
Nienke Bakker, MD, of the Dutch Growth Research Foundation, and colleagues evaluated 40 children with Prader-Willi syndrome treated with GH therapy (20 aged 10 years or younger; 20 older than 10 years) and 41 age- and sex-matched healthy controls to determine serum IGF-I, IGF binding protein-3 (IGFBP-3) and acid-labile subunit (ALS) levels, complex formation and IGF bioactivity between the two groups.
Higher serum values for IGF-I, IGFBP-3, IGF-I/IGFBP-3 ratio and ALS were found among the Prader-Willi syndrome group compared with controls (P < .001). However, the younger Prader-Willi syndrome group had a lower IGF-I/IGFBP-3 ratio compared with the older Prader-Willi syndrome group (P < .001).
Compared with young controls, the young Prader-Willi syndrome group had a higher 150-kD ternary complex formation (P = .022). Similarly, the older Prader-Willi syndrome group had a higher 150-kD ternary complex formation compared with older controls (P = .006). No difference was found between the older and younger Prader-Willi syndrome group for complex formation (P = .222).
The highest IGF bioactivity was found in the young Prader-Willi syndrome group compared with young controls (P < .001) and the older Prader-Willi syndrome group (P = .012). Similar IGF bioactivity was found between the older Prader-Willi syndrome group and older controls.
IGF bioactivity in the Prader-Willi syndrome groups were not correlated with serum immunoreactive IGF-1 levels, whereas there was a positive correlation among controls.
“In GH-treated children with [Prader-Willi syndrome], most of the serum IGF-I is sequestered in the ternary 150 kD complex with ALS and IGFBP-3,” the researchers wrote. “High serum IGF-I levels in GH-treated [Prader-Willi syndrome] children, result only in a higher IGF bioactivity in young children, but in a normal IGF bioactivity in older children compared to healthy controls. In young GH-treated [Prader-Willi syndrome] children, the high IGF bioactivity is related to the increase in BMI and probably transient, but the long-term clinical consequences need further research. In older GH-treated [Prader-Willi syndrome] children, our data are reassuring. IGF bioactivity in GH-treated [Prader-Willi syndrome] children show a wide variation and a disrupted correlation with immunoreactive IGF-I levels, which makes immunoreactive IGF-I levels an inappropriate indicator of GH dosing in these children.” - by Amber Cox
Disclosure: The study was funded in part by Pfizer.
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