Background: Prader-Willi syndrome (PWS) is a neurogenetic disorder characterized by muscular hypotonia, psychomotor delay, obesity and short stature. Several endocrine abnormalities have been described, including GH deficiency and hypogonadotrophic hypogonadism. Published data on thyroid hormone levels in PWS children are very limited. Objective: To evaluate thyroid function in children with PWS, before and during GH treatment. Design/patients: At baseline, serum levels of T4, free T4 (fT4), T3, reverse T3 (rT3) and TSH were assessed in 75 PWS children. After 1 year, assessments were repeated in 57 of the them. These children participated in a randomized study with two groups: group A (n = 34) treated with 1 mg GH/m2/day and group B (n = 23) as controls. Results: Median age (interquartile range, IQR) of the total group at baseline was 4.7 (2.7-7.6) years. Median (IQR) TSH level was -0.1 SDS (-0.5 to 0.5), T4 level -0.6 SDS (-1.7 to 0.0) and fT4 level -0.8 SDS (-1.3 to -0.3), the latter two being significantly lower than 0 SDS. T3 level, at 0.3 SDS (-0.3 to 0.9), was significantly higher than 0 SDS. After 1 year of GH treatment, fT4 decreased significantly from -0.8 SDS (-1.5 to -0.2) to -1.4 SDS (-1.6 to -0.7), compared to no change in untreated PWS children. However, T3 did not change, at 0.3 SDS (-0.1 to 0.8). Conclusions: We found normal fT4 levels in most PWS children. During GH treatment, fT4 decreased significantly to low-normal levels. TSH levels remained normal. T3 levels were relatively high or normal, both before and during GH treatment, indicating that PWS children have increased T4 to T3 conversion.,
Clinical Endocrinology
Erasmus MC: University Medical Center Rotterdam

Festen, D., Visser, T., Otten, B., Wit, J. M., Duivenvoorden, H., & Hokken-Koelega, A. (2007). Thyroid hormone levels in children with Prader-Willi syndrome before and during growth hormone treatment. Clinical Endocrinology, 67(3), 449–456. doi:10.1111/j.1365-2265.2007.02910.x