Congenital hypothyroidism

The Adult Endocrinology Clinic provides diagnosis and follow-up for adult patients with an endocrine problem, that is, a condition affecting the secretion of a hormone (excessive or insufficient secretion) and/or the gland that secretes it. The department therefore manages conditions affecting the thyroid, parathyroid glands, adrenal glands, gonads (ovaries and testicles), and pituitary gland. 

Since 2016, the Endocrinology Department of Erasme Hospital, in association with the Queen Fabiola Children’s University Hospital (HUDERF) for paediatric care, has been part of ENDO-ERN (European Reference Network for Rare Endocrine Conditions), the European Reference Network for rare endocrine diseases.

This network aims to improve access to high-quality care for patients with rare endocrine disorders. It supports clinical research and contributes to the creation of registries listing patients receiving follow-up for rare conditions, in order to promote knowledge sharing and improve clinical practice. 

The management of rare endocrine diseases is multidisciplinary. Regular consultations are organised to discuss complex cases, with numerous specialists within our institution, as well as during virtual consultations with recognised European experts through the ENDO-ERN network or during international multidisciplinary case meetings (France).

Some endocrine diseases begin at birth or during childhood and require lifelong treatment and follow-up. Transition consultations have been provided for many years with our paediatric colleagues at HUDERF to ensure the smoothest possible transition from paediatric to adult care.

Rare congenital thyroid diseases are conditions that are most often present from birth and affect the functioning of the thyroid gland. In most cases, they are congenital hypothyroidism, meaning insufficient production of thyroid hormones. 

Thyroid hormones are essential for growth, but also and above all for the normal development of the brain during fetal life and childhood. In adulthood, they are primarily involved in regulating body temperature (thermoregulation), controlling metabolism (energy expenditure), fertility, intestinal transit, heart rate and mood. Hypothyroidism occurring in adulthood is most often acquired and has various causes (autoimmunity, thyroid surgery, medication, etc.). It does not fall into the category of rare endocrine diseases, unlike congenital hypothyroidism.

The latter may be caused by an absent thyroid (agenesis), an abnormally formed thyroid (dysgenesis), or a defect in the synthesis of thyroid hormones resulting from a mutation in one of the key enzymes (proteins) involved in hormone production. They are most often detected very early, during the first days of life, through neonatal screening. This enables rapid and effective management, preventing the harmful effects of thyroid hormone deficiency on the child’s brain and musculoskeletal development. During pregnancy, the mother provides the fetus with thyroid hormones, thereby compensating for the defect in the fetal thyroid’s hormone synthesis. However, once born, the affected baby no longer benefits from its mother’s thyroid hormones and must therefore promptly receive oral hormone replacement therapy.

Another category of rare congenital thyroid diseases consists of disorders of the metabolism, transport and action of thyroid hormones, including syndromes of resistance to thyroid hormones. These conditions are very rare (1/19,000–1/40,000 births) and are caused by genetic abnormalities affecting one of the thyroid hormone receptors (there are two types). Thyroid hormones are produced in sufficient quantities, but are unable to act optimally in tissues containing the mutated receptor (brain, liver, heart, muscle and bone). The severity and type of symptoms vary considerably depending on the mutation. For the most common forms of these rare disorders, which are also the least severe, diagnosis is most often made following so-called “discordant” thyroid function tests (with an unusual profile) performed during routine blood tests or as part of family screening after a known familial mutation has been identified. 

Congenital hypothyroidism is screened for in newborns. A drop of blood is taken from the newborn’s heel between the 2nd and 5th day of life and placed on filter paper before being analysed. Parents are recalled for an endocrinology consultation if the screening test result is abnormal. Additional tests are performed to confirm the diagnosis (a follow-up blood test) and determine its cause (thyroid ultrasound and scintigraphy). Treatment consists of early replacement therapy with thyroid hormones, started in the first days of life. This treatment is simple, well tolerated and enables the child to develop normally. As with acquired hypothyroidism, the aims of continued follow-up into adulthood are to ensure proper metabolic function, fertility and an optimal quality of life in all areas (physical, psychosocial and professional).
Regular clinical and biological follow-up is essential in order to adjust the doses as the child grows, as well as in response to changing needs in certain situations (weight fluctuations, interactions with other medicines, digestive absorption problems, fertility, pregnancy, etc.).

Medical follow-up must continue throughout life. Providing patients and families with information and support is essential to ensure treatment adherence and long-term quality of life.

In the most common cases of resistance to thyroid hormones, symptoms are mild and patients generally do not require specific treatment. However, this is a difficult diagnosis to make and requires the exclusion of other conditions through specific tests (including genetic analysis for confirmation), with a risk of diagnostic error that may lead to unnecessary thyroid surgery or drug treatment. Follow-up is also essential, as symptoms may evolve and require drug treatment.

During adolescence, a gradual preparation for the transition to adult care is organised. This stage helps strengthen the young patient’s autonomy, ensure continuity of medical follow-up, and transfer all the necessary information to the specialised adult service. The transition is planned in collaboration with the patient, their family, and the paediatric and adult care teams.

Patients are treated by a qualified adult endocrinologist. Hormone assays and genetic tests are carried out in a specialised laboratory. Genetic counselling is offered. An on-call service is available 24 hours a day. Our centre is actively involved in improving knowledge and care for patients with rare endocrine diseases.

A local registry of cases of congenital hypothyroidism and thyroid hormone resistance has been established, and the number of new cases managed is continuously reported to the European ENDO-ERN registry. The aim is to optimise follow-up practices and compare care between different specialised centres. The team receives ongoing training, participates in congresses and seminars, initiates and collaborates on single-centre and multicentre studies, and publishes in the field of thyroid disorders. It also provides training and teaching for students and doctors in training.