Ten-year longitudinal study of thyroid function in children with Down's syndrome.

Background/aims: The natural history of thyroid function in children with Down's syndrome is relatively unknown. We hypothesized that in these patients the occurrence of thyroid dysfunction rises during development.

Methods: Thyroid function was assessed yearly in 145 children with Down's syndrome, all followed from birth up to 10 years of age. Heteroskedastic binary and ordinary logistic regression for repeated measures was used to evaluate the relationship of thyroid function with continuous time.

Results: Congenital hypothyroidism was detected in 7% of cases. The probability of acquired thyroid dysfunction increased from 30% at birth to 49% at 10 years (p < 0.001). The subclinical hypothyroidism was nearly stable during the follow-up. The probability of hypothyroidism increased from 7 to 24% at 10 years (p < 0.001). Positive anti-thyroglobulin antibodies were associated with higher odds of more severe hypothyroidism (odds ratio 3.6). Positive anti-thyroid peroxidase antibodies were a better predictor of more severe hypothyroidism (odds ratio 6.1). Diffuse hypoechogenicity on thyroid ultrasound was found in 34 out of 145 children.

Conclusion: The probability of thyroid dysfunction increasing during development is higher than previously reported. Such children should be carefully monitored annually to early identify thyroid dysfunction.