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Down Syndrome Abstract
of the Month: May 2005

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The effect of thyroxine treatment started in the neonatal period on development and growth of two years old Down syndrome children: a randomized clinical trial.

van Trotsenburg AS, et al
J Clin Endocrinol Metab. 2005 Mar 8

Academic Medical Center, University of Amsterdam, Departments of Paediatric Endocrinology, Paediatrics and Cardiology, Amsterdam, Netherlands; Department of Paediatric Psychology, University of Tilburg, Netherlands.

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Context: Young Down syndrome children appear to have a mild form of congenital hypothyroidism that is rarely detected by neonatal screening and usually left un-treated. Objective: To investigate the effects of thyroxine treatment on development and growth of young Down syndrome children. Design, setting, and participants: Single-center, randomized, double-blind, 24-months trial (enrollment June 1999-August 2001) with nationwide recruitment, comparing thyroxine administration with placebo in 196 Down syndrome neonates. Intervention: Neonates were randomly assigned to treatment for two years with either thyroxine (N = 99; initial dose 8 microgram per kg) or placebo (N = 97). Daily thyroxine doses were adjusted at regular intervals to maintain plasma TSH in its normal and FT4 concentrations in its high-normal range. Placebo dose adjustments mirrored those of thyroxine. Main outcome measures: The primary outcome was mental and motor development at age 24 months, assessed with the Bayley Scales of Infant Development II. Results: At age 24 months, the developmental testing results of 90 thyroxine-treated and 91 placebo-treated children were available for analysis. The thyroxine treated children had a 0.7 month smaller delay in motor developmental age, corresponding to a difference of 7 motor developmental index points. The mental developmental age delay was also 0.7 month smaller in the thyroxine group, but lacked statistical significance. Thyroxine treated children had greater gains in length and weight. Conclusions: The data of our study provide evidence to support the hypothesis that thyroxine treatment may improve development and growth of young Down syndrome children. Thyroxine treatment should be considered in Down syndrome neonates, to maximize their early development and growth.

My comments:

This study was spurred by a previous study in 2003 by the same group of investigators which reported that out of 284 newborns with DS in the Netherlands, the mean total thyroid levels were lower than the mean in babies without DS. It's a significant credit to this group that they were able to carry out a two-year double-blinded controlled study on the topic. If this finding is confirmed through another group of infants, preferably one in a different geographical area, then we've got a very good argument for starting all newborns with DS on thyroid supplementation.

While we're waiting, all parents of newborns with DS should make sure that the baby's doctor checks a thyroid level at birth, at six months of age, one year of age and yearly thereafter.

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