This study set out to investigate the natural history of thyroid function in adults with Down syndrome as there is currently a lack of good long-term follow-up data. The study team looked at annual thyroid function tests in 200 adults with Down syndrome over a 15-year period.

They found that in healthy adults with Down syndrome there is a gradual increase in thyroxine and a possible gradual decline in thyroid-stimulating hormone as people get older

Over the 15 year period, the incidence for definite hypothyroidism was low. The team found that subclinical hypothyroidism did not lead to the onset of definite hypothyroidism

The authors conclude that incidence of thyroid dysfunction is less than would be expected from other prevalence studies. They suggest that such studies may have overstated the association between thyroid dysfunction and Down syndrome.

They recommend that routine screening for adults with Down syndrome who are euthyroid (having normal thyroid gland function) could be reduced to every 5 years rather than current policy of doing such screening every 1–2 years.

Fifteen-year follow-up of thyroid status in adults with Down syndrome, Prasher, V et al, in Journal of Intellectual Disability Research, 55: 392–396