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Thyroid Morphology and Function in Adults with Untreated Isolated Growth Hormone Deficiency

Division of Endocrinology, Federal University of Sergipe (M.R.S.A., P.R.S.A., L.M.A.N., V.S.C., E.C.O.O., M.H.S.O., A.H.O.S., M.H.A.-O.), Aracaju, SE Brazil 49060-100; and Division of Endocrinology, The Johns Hopkins University School of Medicine (R.S.), Baltimore, Maryland 21287

Address all correspondence and requests for reprints to: Dr. Roberto Salvatori, Division of Endocrinology, Johns Hopkins University, 1830 East Monument Street, Suite 333, Baltimore, Maryland 21287. E-mail: salvator{at}jhmi.edu.

Objective: GH influences thyroid function and anatomy. Although goiter is frequent in acromegalic patients, the effects of GH deficiency (GHD) are difficult to assess, because hypopituitaric subjects who lack GH often also have a partial or complete deficit of TSH.

Study Design: We studied thyroid morphology and serum levels of thyroid hormones in adult members of a large Brazilian kindred with untreated isolated GHD due to a homozygous mutation in the GHRH receptor gene (GHRHR; nine men and 15 women; GHD group) and compared them to subjects heterozygous for the same mutation (eight men and 10 women; HET group) and subjects homozygous for the wild-type allele [seven men and 11 women; control (CO) group].

Results: GHD subjects had a smaller thyroid volume (TV) than HET and CO. The TV of the HET group was intermediate between those of the GHD and CO groups. When TV was corrected by body surface area, it remained smaller in the GHD and HET groups than in the CO group, but the difference between GHD and HET groups disappeared. The GHD group had lower serum T₃ levels than the CO group and higher free T₄ levels than HET and CO groups.

Conclusions: Individuals with severe untreated GHD due to a homozygous GHRHR mutation and heterozygous carriers of the same mutation have smaller TV than normal subjects, suggesting that GH has a permissive role in the growth of the thyroid gland. In addition, GHD subjects have reduced serum total T₃ and increased serum free T₄, suggesting a reduction in the function of the deiodinase system.

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