Endocrine Abstracts

Children diagnosed with either Growth Hormone deficiency (GHD) or Turner syndrome (TS) are both treated with GH titrated against either weight or area. The response to such treatment however, is highly variable and, at least in part, diagnosis dependent. The precise mechanisms underlying this variability are unknown. As basal GH levels differ between GHD and TS and, as GH elicits its effects through changes in gene expression, the basal gene expression profiles of GHD and TS subjects may influence their response to GH treatment. We have therefore compared basal gene expression profiles between GHD and TS subjects.

Blood was collected from patients (GHD n=3; TS n=3) prior to initiating GH treatment (22–45 μg/kg/d). Peripheral blood mononuclear cells (PBMCs) were harvested, stored at −80  °C and all samples were processed simultaneously. RNA was extracted (RNAeasy, Qiagen) and amplified prior to hybridisation to Affymetrix HG-U133 Plus 2 oligonucleotide arrays. Averaged normalised data were used to determine the fold difference (FD) in expression levels in GHD relative to TS subjects (GHD/TS).

Under basal conditions and using a cut off criteria of: expression >100 in either GHD or TS and FD >2 or <0.5, 192 probe sets were identified representing 163 genes. These probes included the previously reported GH-sensitive genes: ATF3, GADD45, NFKB1A and NR4A1 (all lower in GHD than TS). Using a more stringent criteria (expression >100 in both GHD and TS and FD >5 or <0.2), 16 probes remained (14 genes) including genes for 5 transport proteins (haemoglobin delta, gamma and mu and 2 solute carrier family members SLC4A1 and SLC25A37; all higher in GHD than TS) and ATF3 (lower in GHD than TS).

In conclusion: 1) PBMCs provide a readily available source to investigate gene expression patterns, 2) we have identified genes with marked differences in basal expression between GHD and TS subjects, 3) array technology may provide insights into possible genes responsible for the differential responses to GH in GH-treated children.