Lower neonatal screening thyroxine concentrations in Down syndrome newborns

Abstract

There is an unexplained higher incidence of congenital hypothyroidism (CH) detected by T4-based neonatal screening programs and a very high prevalence of (mild) plasma TSH elevation in young children with Down syndrome (DS). To determine whether newborns with DS have decreased blood T4 concentrations at the time of the neonatal screening, we conducted an observational study in a large and representative cohort of Dutch children with DS born in 1996 and 1997. CH screening results (T4, TSH, and T4-binding globulin concentrations) were analyzed in comparison with clinical information obtained by interviewing the parents and data from the general newborn population and a large control group. The mean T4 concentration of the studied children with DS (n = 284) was significantly decreased. The individual T4 concentrations were normally (Gaussian) distributed but shifted to lower concentrations. This could not be explained by prematurity, nonthyroidal illness, or iodine exposure. Mean TSH and T4-binding globulin concentrations were significantly increased and normal, respectively. The decreased T4 concentration, left-shifted normal distribution, and mildly elevated TSH concentrations point to a mild hypothyroid state in newborns with DS and support the existence of a DS-specific thyroid (regulation) disorder. The question remains whether this contributes to the brain maldevelopment.