Deletion of a portion of the long arm of chromosome 18 is associated with poor growth, central nervous system hypomyelination and mental retardation(18q- syndrome). The mechanisms leading to these features are unknown; however, all could be related to inadequate/abnormal thyroid hormone(TH) production.

In order to further characterize the neuroendocrine axis in 18q- children, a TH test battery was performed on 6 children (age range 1-8 years, 4 female, 2 male). T4 and free T4 were normal and none were on TH replacement. Two had normal responses to clonidine and arginine (peak GH >10 ng/ml), and four had low responses (peak <7). Two GH deficient children were on GH treatment.

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