Growth parameters, growth hormone (GH) response to clonidine and circulating insulin-like growth factor-I (IGF-I), free thyroxine (FT4) and cortisol concentrations in relation to glycaemic control in children with insulin-dependent diabetes mellitus.

Abstract

The objective of this paper was to determine the effect of glycaemic control and endocrine functions on linear growth in children with IDDM. We studied 45 prepubertal children with IDDM (30 males, 15 females) over 1 year period. The mean +/- SD for age of onset and duration of IDDM were 6.2 +/- 2.3 years and 3.5 +/- 1.3 years, respectively. At each clinic visit (every 3 months), glycaemic control was assessed by measuring glycosylated haemoglobin (HbA1C). Growth hormone and cortisol responses to high dose clonidine (0.15 mg/m2) and ACTH, respectively, were evaluated and circulating concentrations of free thyroxine (FT4) and TSH estimated. The average insulin dose (unit/kg/day) during this period was calculated for each patient. Growth was assessed by determining both height standard deviation score (HtSDS) and growth velocity standard deviation scores (GVSDS) and bone age determined according to the atlas of Greulich and Pyle. Two-hundred-and-fifty age- and sex-matched normal children served as controls for growth data, and 20 normal age-matched children and 20 normal children with short stature (NVSS) served as controls for the hormonal studies. Growth velocity (GV) (cm/year) and GVSDS were significantly lower in children with IDDM compared to normal children, and significantly lower in children with poorly controlled diabetes compared to those with good glycaemic control. GV and GVSDS were inversely correlated to HbA1C (r = -0.356, P < 0.01 and r = 0.335, P < 0.01 respectively). GVSDS was correlated with serum IGF-I (r = 0.22, P < 0.01), FT4 (r = 0.321, P < 0.01) and inversely with basal GH (r = -0.362, P < 0.01) concentrations, but was not correlated with cortisol levels or peak GH concentrations in response to clonidine. GVSDS was correlated with HtSDS (r = 0.222, P < 0.01) and inversely with age (r = -0.43, P < 0.05). There was no significant correlation between GVSDS on the one hand and weight gain or body mass index (BMI) on the other hand. Peak GH response to clonidine was correlated with BMI (r = 0.68, P < 0.001) and insulin dose/kg/day (r = 0.602, P < 0.01). This study confirms that in children with IDDM linear growth velocity is dependent on the age of the child and the degree of glycaemic control, as well as on growth promoting hormones such as IGF-I and FT4. High BMI is associated with more GH secretion in response to clonidine, this might explain the higher requirements of insulin/kg in children with IDDM and high BMI.