Failure to thrive (FTT) in infants with Prader-Willi syndrome and long-term effects of GH-treatment on FTT

CONTEXT: Failure to thrive (FTT) with feeding difficulties and hypotonia are well-known features in infants with Prader-Willi syndrome (PWS). Limited studies reported the percentage of infants with FTT and it is unknown whether growth hormone (GH)-treatment affects body composition of infants with or without FTT differently. OBJECTIVE: To evaluate the percentage of infants with PWS with FTT from birth to age 6 months and to investigate the 5-year GH effects on body composition in infants with or without FTT at GH-start. METHODS: We defined FTT as weight-for-length <-2 SDS and evaluated the percentage of infants with FTT in a group of 54 infants from birth to age 6 months. In addition, we investigated in 166 children the 5-year GH effects on body composition, comparing children with and without FTT at GH-start. All infants were treated with 1.0 mg GH/m2/day (~0.035mg/kg/day). Body composition was determined by Dual energy X-ray Absorptiometry (DXA). RESULTS: From birth to age 6 months, 29% of infants had FTT at 1 month, 20% at 3 months, and 16% at 6 months. At GH-start, at a median age of 1.03 (IQR 0.45,1.89) year, 12% (20/166) had FTT (FTTGH-start). Infants with FTTGH-start had a lower lean body mass index (LBMI) compared to non-FTTGH-start, but a greater catch-up in LBMI in the first year of GH, resulting in a similar LBMI as the non-FTTGH-start after 5 years of GH-treatment. Children with FTTGH-start had lower FM% after 5 years of GH-treatment, but this difference disappeared after including covariates. CONCLUSIONS: Twenty-nine percent of infants had FTT at 1 month, 20% at 3 months, and 16% at 6 months. Twelve percent had FTT at the start of GH-treatment. Children with FTT at GH-start showed greatest LBM improvement during GH-treatment, resulting in a similar LBM after 5 years of GH-treatment as those without FTT at GH-start.