Endocrine Abstracts

Paediatric Graves’ disease (PGD) is an uncommon autoimmune disorder with a multifactorial origin. Although, in some autoimmune endocrinophaties the seasonality of month of birth (MOB) distribution differed from the general population, this association has not been study in PGD. The aim of this work was to analyse the impact of seasonality of MOB on PGD incidence in Portugal.

In 2013, the Portuguese Paediatric Society of Diabetes and Endocrinology undertook a national multicentric study of the PGD (153 cases). We compared the distribution of MOB within this study with the Portuguese population (data from the National Institute of Statistics). Since, the mean age at diagnosis was 11 years, we restricted the study period up to 2001 to correct for that variation (125 cases). Statistical analysis was performed with STATA Software, version 12.0. Walter and Elwood method was used because it takes into account the population at risk.

A total of 125 cases of PGD born between 1983 and 2001 were recorded (75% females) compared to 2 271 523 births (49% females). Among PGD, the percentage of observed to expected births did not differ across the 12 months (P=0.8). Nevertheless, the smoothed birth-month estimates demonstrated a non-significant (NS) excess of births from September to April, and a deficit from May to July. The evaluation of the subgroup with higher TRABS titters at diagnosis (50 cases with TRABS ten times the upper limit of normal), did not show a higher incidence compared to the Portuguese population (P=0.7).

This was the first population-based study that analysed the impact of seasonality of MOB in the incidence of PGD. Despite a trend to a higher incidence of PGD in children born between September and April, no uniform seasonal pattern of MOB in PGD was observed in this sample of the Portuguese population. We thank the Portuguese Paediatric Society of Diabetes and Endocrinology for allowing the study data to be used in this work.