OBJECTIVE: To evaluate the prevalence of abnormalities of thyroid function and 
morphology in a cohort of patients with Williams syndrome (WS).
METHODS: Serum concentrations of free-T3, free-T4, TSH, thyroperoxidase 
antibodies (TPOA) and thyroglobulin antibodies (TgA), as well as 
ultrasonographic data, of 20 patients with WS (12 females and eight males), aged 
1.7-34.9 years, were evaluated.
RESULTS: Three cases (15%) of subclinical hypothyroidism were identified. Overt 
hypothyroidism was diagnosed in two cases (10%). Thyroid antibodies were 
negative in all patients. Fourteen patients (70%) showed thyroid hypoplasia 
involving the entire gland. In these patients, the left thyroid lobe appeared 
usually, but not significantly, reduced compared with the right thyroid lobe. 
One patient (5%) showed thyroid hemiagenesis. Only five patients (25%) showed a 
thyroid with normal volume, and of these five, one patient showed marked thyroid 
hypoplasia of the left lobe. In all WS patients with diagnosis of subclinical or 
overt hypothyroidism, thyroid hypoplasia was detected. No cases of subclinical 
or overt hypothyroidism were found in WS with normal thyroid volume.
CONCLUSIONS: This study confirms the presence of alterations of thyroid function 
in WS and also suggests the frequent occurrence of abnormalities of thyroid 
morphology in these patients. Patients with WS should be monitored for thyroid 
function and a thyroid ultrasound screening should be considered, especially in 
those patients with changes in thyroid function.