Aim: To determine whether primary or secondary growth hormone (GH) deficiency has a causative role in linear growth retardation, a key feature in Rett syndrome (RTT).
Methods: In 38 patients with Rett syndrome a variable set of investigations was performed including assays of growth and thyroid hormones, gonadotropins, gonadal and adrenal steroids and determination of bone age. Not all measurements were attainable from all patients. In three patients the 24-h growth hormone secretion profile was evaluated using the pulsar method.
Results: The bone age determined in 24 patients was found to be normal in 8, retarded in 9 and accelerated in 7 patients. Insulin-like growth factor (IGF)-1 was low in 8 out of 23 patients. IGF-binding protein (IGFBP)-3 and insulin and arginine-stimulated growth hormone secretion were both normal, indicating normal GH secretion in the majority of patients. The 24-h GH secretion profile in the first patient showed a normal day/night rhythm and a normal increase in nocturnal GH secretion. The second patient's overall GH secretion was normal but there was no day/night rhythm. The third patient showed borderline low GH secretion. Normal age-appropriate plasma values were found for the thyroid hormones (T4, TSH), TSH-night rhythm, oestradiol, prolactin and cortisol (08.00, 18.00).
Conclusion: Our study provides no evidence that growth retardation in RTT is caused by growth hormone deficiency. A disturbed hypothalamic control cannot be excluded but it is unlikely that this is the major cause of growth retardation in RTT.