Insulin-like growth factor-I in cerebrospinal fluid and serum in Rett syndrome

Rett syndrome is a neurodevelopmental disease characterized by failure of somatic and brain growth. The insulin-like growth factor system mediates most actions of growth hormone. Evidence that it plays an important role in early development of the brain is increasing. The aim of the study reported was to assess the role of the insulin-like growth factor system in the pathogenesis of Rett syndrome. We measured insulin-like growth factor-I levels in serum (8 patients, mean age 9.1 years) and cerebrospinal fluid (13 patients, mean age 7 years) using a sensitive radioimmunoassay method and compared them with those in age-matched controls (13 and 26 patients, respectively). Neither serum nor cerebrospinal fluid insulin-like growth factor-I levels differed from those in controls. We also measured insulin-like growth factor binding protein-3 levels in serum (in 9 patients and 8 controls) and in cerebrospinal fluid (in 12 patients and 11 controls) and serum growth hormone levels (in 8 patients and 11 controls); the levels in patients did not differ from those in controls. We found no significant correlation between serum and cerebrospinal fluid insulin-like growth factor-I in Rett syndrome. This may indicate an independent role of insulin-like growth factor system in the central nervous system, making serum insulin-like growth factor-I measurement unreliable as an indicator of disturbed function in the central nervous system. Our results did not support the notion that a defective insulin-like growth factor-I system explains the lack of somatic and brain growth in Rett syndrome.