Pathogenesis, natural course and therapeutic management of subclinical hypothyroidism (SH) in Down's syndrome (DS) remain object of debate in literature. In the present study thyroid function, antithyroid antibody (ATA) prevalence and serum lipid concentrations were investigated in a group of 344 Down patients (DP) and data were compared with those obtained from a control group of 257 age and sex matched healthy subjects. Thyroid function and ATA prevalence were also studied in 120 parents of DP. SH prevalence was clearly higher in DP (32.5 of cases) than in controls (1.1) and parents (0). Similarly, ATA prevalence was higher in DP (18 of cases) than in controls (5.8) and parents (6.6). In spite of this, no correlation was found in DP between SH and ATA prevalences, since ATA were detected in 18.7 of SH-DP and in 15.8 of euthyroid DP. Thus, circulating ATA were not detected in the majority of SH-DP. No significant differences regarding T4, FT4, T3 and serum lipid levels among SH and euthyroid DP and controls were found. Moreover, TSH levels were only slightly increased, generally less than 10 microU/ml, in most cases of SH-DP. Follow-up was longer than 24 months (range 2-7 years, mean 3.1) in a group of 201 DP: two different patterns of SH course were observed, mainly depending on the presence or the absence of circulating ATA. In particular, 35.7 of ATA-positive SH-DP developed a clinically evident thyroid disease (overt hypothyroidism or hyperthyroidism), while no similar case was recorded among ATA-negative SH-DP.(ABSTRACT TRUNCATED AT 250 WORDS)
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