Published: 2.7.2026
Text: Rowmika Ravi
Editing: Viestintätoimisto Jokiranta Oy
Image: Shutterstock
Author photo: University of Eastern Finland / Studio EveLiisa

A remarkable fact is that 99.9% of human DNA is identical, which means that the difference in us is contributed by the 0.1%. The differences shaping our unique characteristics are mostly beneficial, but a small part of variations in the codes cause rare genetic disorders.

One such group of rare conditions are early-onset thyroid disorders (EOTD) diagnosed at birth, in childhood or during adolescence, in which the thyroid gland produces too much (hyperthyroidism) or too little (hypothyroidism) hormone. Examples include congenital hypothyroidism (CH) and early-onset autoimmune thyroiditis.

A rare gene variant found in our research

Our research focuses on identifying genetic variants causing these disorders in around 200 Finnish patients participating in our study.
To identify disease-causing variants, we use whole-exome sequencing, which reads the genetic code of genes in affected individuals and their family members. Recently, we identified a rare variant in the STAT3 gene in two siblings aged five and 1.5 years who developed very-early-onset autoimmune thyroid disease.

Previously, this STAT3 variant was linked to severe multi-system autoimmune disorders. Our findings showed, for the first time, that the variant could cause autoimmune disease limited only to the thyroid gland at a very early age.

A major focus of our work is CH, which affects 1 in 3,000 newborns. We identified that a variant in SLC26A7 gene is one of the most common causes of familial CH in Finland. Using mouse and cell models, it is seen that the gene helps transport iodide in the thyroid gland, a process essential for thyroid hormone production. When the gene is altered, hormone synthesis is disrupted, leading to hypothyroidism in newborns.

Genetic screening could reduce unnecessary testing

Identifying genetic variants contributes to more personalised disease management. Thyroid hormone is essential for metabolism and especially important in children for brain development, growth, and maturation. Untreated CH can result in intellectual disability and growth problems. Understanding how genes, such as SLC26A7, function may improve treatment options. For example, some patients with SLC26A7-related CH might benefit from iodine supplementation instead of standard hormone replacement therapy. This is a possibility requires further study.

In Finland and several other countries, newborns are screened for CH by measuring thyroid stimulating hormone (TSH) levels at birth. However, some patients require long-term follow-up because symptoms and laboratory results can vary over time, as seen in transient CH or TSH resistance-like disorders. This often means repeated hospital visits and invasive tests, which can be challenging especially for children. Genetic screening could help provide earlier and more accurate diagnosis, identify individuals at risk, and reduce unnecessary testing.

Further research is needed

Despite advances in research, genetic causes are currently identified in only about 50–80% of familial CH and 15-30% of non-familial CH patients. Studies like ours are, therefore, essential to expand the list of genes associated with CH and related clinical symptoms.

Gene function is also influenced by environmental factors, nutrition and lifestyle. Studying the interactions of these factors is necessary in order to gain a holistic understanding of health and disease. The question ‘What is written in the genes about EOTD?’ still has many unanswered aspects, and our research aims to contribute to those answers.

 

 

Rowmika Ravi, PhD, earned her doctoral degree in Molecular Medicine from the University of Eastern Finland, Kuopio, in 2023 with a dissertation entitled ‘Metabolomics and Genomics approaches in cardiovascular diseases’. Currently, she is a post-doctoral researcher at the University of Turku and is investigating the genetics of early-onset thyroid disorders in the Finnish population.

Image: University of Eastern Finland / Studio EveLiisa