DIAGNOSIS OF ENDOCRINE DISEASE: Congenital hypothyroidism: update and perspectives

Molecular defects in thyroid dysgenesis

Congenital hypothyroidism (CH) is a neonatal endocrine disorder that might occur as itself or be associated to congenital extra-thyroidal defects. About 85% of affected subjects experience thyroid dysgenesis (TD), characterized by defect in thyroid gland development. In vivo experiments on null mice paved the way for the identification of genes involved thyroid morphogenesis and development, whose mutation has been strongly associated to TD. Most of them are thyroid-specific transcription factors expressed during early thyroid development. Despite the arduous effort in unraveling the genetics of TD in animal models, up to now these data have been discontinuously confirmed in humans and only 5% of TD have associated with known null mice-related mutations (mainly PAX8 and TSHR). Notwithstanding, the advance in genetic testing represented by the next-generation sequencing (NGS) approach is steadily increasing the list of genes whose highly penetrant mutation predisposes to TD. In this review we intend to outline the molecular bases of TD, summarizing the current knowledge on thyroid development in both mice and humans and delineating the genetic features of its monogenetic forms. We will also highlight current strategies to enhance the insight into the non-Mendelian mechanisms of abnormal thyroid development.

[Epidemiology of congenital hypothyroidism in France: recent data]

Congenital hypothyroidism (CH) is the leading cause of preventable mental retardation. It is mainly due to thyroid dysgenesis or dyshormonogenesis with normally located gland, and detected at birth in developed countries, by mass biochemical screening of newborns. An increase in the incidence of congenital hypothyroidism with a normally located gland has been reported worldwide over the last three decades. The etiology of CH with a normally located gland remains elusive and the factors driving its clinical diversity are largely unknown. A role for known dyshormonogenesis-associated genetic variants or TSH receptor gene variants is well-known, but the possible effects of environmental agents toxic to the fetal and neonatal thyroid gland are currently being investigated.

NEONATAL SCREENING FOR CONGENITAL HYPOTHYROIDISM IN ROMANIA: DATA FROM MEDILOG MEDICAL INFORMATION REGISTRY

Objective

Congenital hypothyroidism (CH) is one of the common preventable causes of intellectual disability in neonates, by early detection through neonatal screening. We present the 8-year experience of the National Institute for Mother and Child Health (INSMC) in using MEDILOG national registry for the neonatal screening of CH.

Methods

Neonatal screening for CH, done by TSH measurement in dried blood spot, is organized in 5 regional centers, each with a reference laboratory.

Results

In 2018 80% of all the newborns, from 80% of the maternity hospitals, were registered in MEDILOG. After re-testing of TSH and T4/FT4 from venous blood in positive cases, the incidence of confirmed CH in 2018 was 1/3576 - 1/ 4746. In INSMC center (which includes 26 counties and Bucharest, out of 41 counties), in 2018 the incidence of positive CH cases at screening was 1/2094 (TSH cut-off ≥17 mIU/L) and of confirmed CH cases 1/3576 newborns. For positive screening cases, the median duration from birth to the INSMC laboratory result was 19 days: median of 9 days between screening and laboratory registration and 6 days between registration and test result.

Conclusion

MEDILOG registry is a practical instrument for monitoring the steps of neonatal CH screening, the incidence of CH, the evolution of the diagnosed cases, for evaluation of iodine deficiency (by neonatal TSH), and also for research, with the aim of improving early disease detection and treatment.