THYROID FUNCTION DISORDERS IN THE CHILD AND ADOLESCENT WITH TRISOMY 21

Thyroid function disorders are the most frequently detected medical complication among patients with trisomy 21, with a reported prevalence ranging from 4-8% in childhood to 50% or more in adulthood. Over 1% of newborns with Down syndrome show clinical and/or biochemical signs consistent with congenital hypothyroidism, which is generally promptly identified by means of the neonatal screening. 30% of patients are diagnosed with transient congenital hypothyroidism, while 70% show a lifelong need for hormonal replacement therapy with levothyroxine. Moreover, non-autoimmune subclinical hypothyroidism is the most frequent finding, with reported prevalence ranging from 23 to 60%. It is still controversial whether subclinical hypothyroidism can be labelled as a pathological condition or the expression of a mere asymptomatic upwards shift of TSH, with no clinical impact. In addition, syndrome-related abnormalities in the mechanisms underlying immune tolerance result in a greater occurrence of autoimmune disorders. Graves’ disease and autoimmune hypothyroidism in Hashimoto thyroiditis are experienced by almost 30% of patients with trisomy 21. Finally, it is frequent that the latter clinical picture switches into hyperthyroidism and vice versa in an unpredictable clinical continuum. Given the increased lifelong risk of experiencing thyroid function disorders in children and adolescents with trisomy 21, a systematic periodic clinical and biochemical assessment is recommended to promptly detect and possibly treat pathological conditions.