Age-related changes in thyroid hormone profile in pediatric patients with Down syndrome

Children with Down syndrome (DS) have a high prevalence of thyroid dysfunction; however, age-related changes in thyroid hormone profiles remain unclear. We investigated the age-related changes in thyroid function in children with DS. We retrospectively analyzed the thyroid function test results of 762 patients with DS aged 3-14 years without known thyroid disease, and compared them with those of 764 age-matched controls with idiopathic short stature. Serum thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) levels and the FT3/FT4 ratio were compared between patients with DS with/without congenital heart disease (CHD) and gastrointestinal malformations. In each age group, the log-transformed TSH distribution exhibited similar standard deviation and kurtosis, but showed consistently higher mean values in patients with DS than in controls. Mean FT3 levels were slightly lower in the DS group, except at ages 11-12 years. Mean FT4 levels were slightly lower in the DS group after 9 years of age. The mean FT3/FT4 ratio was lower in the DS group at ages 3-8 years but normalized after 9 years of age. Patients with DS and CHD had higher TSH levels than those without CHD after 11 years of age, whereas FT3, FT4, and the FT3/FT4 ratio showed no significant differences. A rightward shift in serum TSH distribution was observed in patients with DS without thyroid disease, suggesting that TSH levels are generally high in patients with DS. These variations highlight the need for personalized management of thyroid function in patients with DS.