Endocrine Abstracts

Introduction: In the etiology of thyroid dysgenesis (TD) an interplay between genetic and environmental factors is thought to play a crucial role. Data from previous studies on association between the season of birth and the incidence of TD causing congenital hypothyroidism (mainly agenesis and ectopy) are conflicting. To date, seasonality of births have not been analysed yet in regard to congenital absence of one thyroid lobe (thyroid hemiagenesis, THA).

Patients and Methods: Dates of birth of 102 patients diagnosed with THA were analysed and compared to 102 control subjects with no thyroid pathology matched for age and gender. Both groups were subdivided according to the month of birth (I-XII), season of birth (spring, summer, autumn, winter) and quarter (1–4) of the year. The differences were analysed statistically.

Results: Distribution of the months of birth in the group of patients with THA was asymmetric; smaller number of patients were born in the 4th (X-XII) quarter of the year (19 patients) vs 1st (28 patients), 2nd (29 patients) and 3rd (26 patients). Similarly, smaller number of patients were born in autumn (IX-XI) – 19 patients if compared to other seasons of the year (winter – 27 patients, spring – 27 patients, summer – 29 patients). However, if the studied group was compared to the control group, the difference in the distribution of the months of birth was at the border of statistical significance (P<0.0923). Furthermore, if the studied and control group were subdivided into four quarters or seasons, and then compared, the difference was definitely not statistically significant.

Conclusions: An analysis of the largest so far reported cohort of patients with THA indicate that environmental factors including intrauterine exposure to maternal seasonal viral infections or variable vitamin D availability seem not to play a significant role in pathogenesis of THA.