Random Variability in Congenital Hypothyroidism from Thyroid Dysgenesis over 16 Years in Québec

Abstract

The incidence of CHTD did not vary over the observation period, and its monthly variation was random. Therefore, environmental factors do not appear to play a significant role in the etiology of CHTD.

Space–time clustering of elevated thyroid stimulating hormone levels

“…An increasing temporal trend in incidence of CHT has recently been reported in New However, this is in contrast to research conducted in Quebec, Canada, where no changes in incidence were seen over a 16 year period [4]. A real temporal trend, aside from changes in diagnostic procedures which can lead to increases in incidence [25], suggests either an increasing exposure to an environmental risk factor, or a changing distribution of risk factors among the population.…”

“…An increasing incidence of CHT has been suggested from an analyses of data including that from New York State [2] and Mexico [3], although no similar increase was shown in a similar study of data from Quebec [4]. Previous studies in the United Kingdom have suggested that CHT is more prevalent in Asian sectors of the population and that prevalence has increased [5].…”

“…The sensitivity and specificity of tests such as isotope scanning is suboptimal with potentially misleading information generated by factors such as early thyroxine therapy [18]. 4. Some studies have used thyroxine intervention as confirmation of underlying CHT but the threshold for intervention will vary with time and from clinician to clinician and centre to centre [19].…”

“…However, seasonality also has been not observed in a number of other studies, including those in the North West of England [12], the Netherlands [13], Saudi Arabia [14], Canada [4], Norway, France and Switzerland [9].…”

Morphogenetics of early thyroid development

“…A role of environmental factors affecting thyroid development is, however, still largely hypothetical. On the contrary, the lack of a seasonal variation argues against a significant contribution of the environment (Deladoey et al 2007a). The genetic basis of TD was recently emphasized by the finding of gene copy number variations in 9% of a patient cohort (Thorwarth et al 2010).…”