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23-03-2006 | Thyroid | Article

Growth hormone-thyroid volume link clarified

Abstract

Free abstract

Research findings indicate a critical role for growth hormone (GH) in the determination of thyroid morphology, independent of thyroid-stimulating hormone (TSH) levels.

Roberto Salvatori, from Johns Hopkins University in Baltimore, Maryland, USA, and associates examined the thyroid volumes (TVs) of Brazilian patients with familial isolated growth hormone deficiency (GHD), which causes dwarfism.

These adult patients are ideal for the study of GH influence on TV, as their condition is caused by a homozygous null mutation in the GHRH receptor (GHRHR) gene. Additionally, they had never received GH therapy and had no clinical or biochemical evidence of TSH deficiency, which can also impact on TV.

As well as assessing thyroid morphology and serum levels of thyroid hormones in the nine men and 15 women with an homozygous mutation in the GHRHR gene (GHD group), the scientists evaluated eight men and 10 women who were heterozygous for the GHRHR mutation (HET group). Seven men and 11 women who were homozygous for the wild-type allele (CO group) were also included.

They found that GHD participants had significantly smaller TV than HET or CO individuals, with the average TV of the HET group being between those of the GHD and CO groups.

Height and weight, along with levels of serum insulin like growth factor (IGF) I, were significantly lower in the GHD group than in the HET or CO group.

After adjustment for body surface area, Salvatori and colleagues still found a smaller average TV in the GHD and HET groups than in the CO group, but the difference between the GHD and HET groups disappeared.

"The finding of smaller TV in GHD and HET subjects and its correlation with height and serum IGF-I indicate a critical role of GH in determination of TV," the authors state in the Journal of Clinical Endocrinology & Metabolism.

"If confirmed in other populations, this observation may suggest that serum IGF-I levels should be considered a determinant of thyroid size."