Growth hormone receptor deficiency in humans associates to obesity, increased body fat percentage, a healthy brain and a coordinated insulin sensitivity

Abstract

Background: We have shown that subjects with Laron syndrome (LS) due to growth hormone receptor deficiency (GHRD) and their relatives have comparable brain structure and function; moreover, the brain of individuals affected with GHRD appears like those of younger people. While the functionally absent growth hormone receptor and the diminished concentrations of the insulin-like growth factor-I have been associated to these findings, the role of the insulin-glucose axis is emerging as an unavoidable consideration when determining the aetiology of these observations. In consequence, we decided to search for the potential and discrete associations between the neurological findings and several parameters of carbohydrate metabolism that might exist in the subjects affected with GHRD.

Subjects and methods: Individuals affected with GHRD were compared to relative controls. Besides standard measures of anthropometry, body composition and brain characteristics, the elements of the carbohydrate metabolism (CHO), including glucose, insulin, triacylglycerol and the free insulin growth factor binding protein 1 (IGFBP1) concentrations were determined. In addition, the correlations existing between the parameters of CHO and brain characteristics were established.

Results: Besides the phenotypical characteristics of GHRD subjects, including those of brain structure and function, enhanced insulin sensitivity, and other minor, we observed that the insulin-regulated IGFBP1 had a consistent negative correlation with the main elements of the carbohydrate metabolism only in the individuals affected with the disease, and not in their relatives.

Conclusions: When compared to their relatives, subjects with GHRD who lack the counter-regulatory effects of GH on the insulin axis, despite their increased risk factor profile due to obesity and increased body fat percentage, have a healthy and younger looking brain associated to an enhanced and coordinated insulin sensitivity. Furthermore, it was observed that in the GHRD subjects IGFBP1 negatively correlates, in a constant and systematic manner, with the main elements of the CHO metabolism. These observations suggest a direct relationship between an efficient insulin sensitivity and a healthy brain.

Keywords: Brain; Growth hormone receptor deficiency; Insulin-like growth factor binding protein 1; Laron syndrome; Obesity.