Follow-up to Adult Height of a Cohort of Subjects Born Small for the Gestational Age and Treated With Growth Hormone

The small for gestational age (SGA) concept includes babies born to term whose weight and/or height is lower than two standard deviations (SD) below the mean. Pathologically short stature is understood as a stature of 2.5 SD below the mean for their age and an expected adult height adjusted to the parental height of one SD below the mean. These SGA children with a pathological short stature after four years of age are unsuitable for GH treatment. In fact, there is no other efficient treatment for short stature and insufficient development of these children other than GH. In addition to short stature, the SGA syndrome also includes resistance to insulin with the consequent risk of developing type 2 diabetes and other interrelated metabolic alterations like dyslipidemia and hypertension; and the glucose-insulin-insulin growth factors (IGFs)-proteins transport axis regulate growth as well as foetal metabolism and development. Independent from the possible maternal environmental causes, those born with SGA have low levels of somatomedin C (IGF-I) and its transport protein [Insulin-like growth factor binding protein 3 (IGFBP-3)] as well as fasting hyperinsulinemia. The low levels of IGF-1 and IGFBP-3 persist in those that do not present a catch-up growth and the insulin resistance is secondary to the somatotrope axis. Treatment with GH increases IGF-I and IGFBP3 levels but also the plasmatic level of fasting insulin and the long term net result of this combination is unknown.

An analysis has shown, that although during the first 2 years of GH treatment, there are no signs of glucose intolerance even though there is less sensitivity to insulin, there could be a greater incidence of type 2 diabetes in deficient children that have been treated with GH for a longer period. Treatment with GH, of children born SGA that have not caught-up their growth at 4 years of age, in the majority of cases achieves a good initial growth speed increase in order to continue to grow within normal limits and end up with an adult height that falls within normal. This is achieved with an authorised daily dose of 0.035 mg/kg (1 mg/m2/day). However, the question regarding the possible metabolic consequences of GH treatment of those born SGA remains unanswered in both forms, to find out if GH treatment increases or reduces resistance to insulin and other associated metabolic parameters and therefore, the risk of developing type 2 diabetes. Continued monitoring to adult height of a cohort of subjects born with SGA and treated with GH is the most efficient, easy and comfortable tool for answering that question.

OBJECTIVES

Primary objective:

• To quantify the evolution of insulin sensitivity from the start of treatment with GH until adult stature is reached. Sensitivity or resistance to insulin is calculated using the HOMA-IR model (Homeostasis Model Assessment for Insulin Resistance) which is a reliable and easy mathematical model that uses the following formula: insulinemia (μU/ml) x glycemia (mmol/l)/22.5.

Secondary objectives:

• To find predictive factors for the possible changes in insulin sensitivity and its complex associated obesity, hypertension and high triglycerides type dyslipidemia with low high density lipoprotein (HDL)-cholesterol. For this, a relation between these metabolic factors and auxological parameters is to be identified.

1. The following are considered independent or predictive variables:

• Speed of growth in cm/ year
• Standard deviations of height
• IGF-I in ng/ml
• IGFBP-3 in ng/ml b. The dependent variables will be:
• HOMA-IR value
• Triglycerides rate in mg/dl / HDL-cholesterol in mg/dl
• Blood pressure in mmHG
• Body mass index

This is an observational study of a single cohort, without the possibility of a control group because those born with SGA, who experience a catch-up growth and enter normal auxology within the first four years of life are not subjected to a paediatric follow-up similar to those that do not catch-up to normal auxology and are treated with GH. Therefore, the same auxological and metabolic test results are not available in standard care. The collection of said parameters requires an "ad hoc" intervention and the study would be experimental or interventional. The observation period of this study encompasses from the start of treatment with GH up to a year after finishing the treatment for any reason. The starting age as well as the time treatment is ended will vary per subject. However, most subjects finish treatment once adulthood is reached. In accordance with clinical studies, the average observation period will probably be about 10 years. After the basal data is made available, the collection of data afterwards will be carried out once a year per subject.