Current Knowledge on Growth Hormone and Insulin-Like Growth Factors and their Role in the Central Nervous System: Growth Hormone in Down Syndrome

Abstract

Down syndrome (DS) is a chromosomal disorder associated with short stature and psychomotor delay. Growth hormone (GH) and insulin-like growth factor I (IGF-I) are of interest in DS as the pronounced growth retardation coincides in time when GH becomes essential for growth. Simultaneously mean intelligence quotient (IQ) decreases markedly. There is no evidence of a general GH deficiency in children with DS, but suboptimal endogenous production of GH and selective deficiency of IGF-I have been demonstrated. GH and IGF-I are important brain growth promoting factors. IGF receptors are present in brain cells from foetuses with DS, but there is no information as to whether disturbances of intracerebral GH binding or IGF-I production may contribute to the brain dysfunction in DS. GH therapy normalized growth velocity and improved fine motor performance in young children with DS, but the limited therapy was followed by a marked catch-down growth and lacked effect on final height. In adolescents with DS treatment with GH during early childhood show some positive late effects, where subjects previously treated had greater head circumference and improved performance regarding cognitive function and motor skills. Few studies have addressed the effect of GH in Down syndrome. Nevertheless, GH has been designated beneficial effects on cognition, energy, mood and behaviour through extensive studies in several other conditions and it is not unlikely that GH may have similar effects in DS. It should be emphasised that even small changes in psychomotor attainment may be of substantial importance in a developmentally delayed population.