Rare diseases
Congenital hypothyroidism affects approximately 1 in 2,000 to 4,000 births, with differing prevalence by ethnicity. This is because the disease is more common among children of Asian, Native American, or Hispanic origin.
Nearly all screening programs report a female preponderance, with a female/male ratio approaching 2/1.
Congenital hypothyroidism in newborns is defined as a deficiency of thyroid hormones present at birth. It is one of the most common preventable causes of intellectual disability worldwide.
What causes hypothyroidism in newborns is an abnormal development of the thyroid gland (dysgenesis) in about 85% of cases, or by a disorder of thyroid hormone biosynthesis (dyshormonogenesis) in 10-15% of cases. These disorders cause primary hypothyroidism and thyroid stimulating hormone (TSH) concentrations are high. Secondary hypothyroidism, or central hypothyroidism, is rarer and results from TSH deficiency. However, peripheral congenital hypothyroidism is due to an abnormality in the transport, metabolism, or action of thyroid hormones. There are also forms of transient congenital hypothyroidism. They most often affect premature children born in areas of endemic iodine deficiency, while in Western countries, they are most often due to iodine overload or placental passage of maternal antibodies blocking the thyroid. These transient forms usually resolve spontaneously within months or years.
Thyroid hormones play a key role in psychomotor development and growth, in the body’s thermoregulation process, in maintaining muscle tone, or in bowel movements.
Symptoms of congenital hypothyroidism in newborns are often absent, although some are mildly hypotonic and sleep more. Specific symptoms often appear only after several weeks. They include difficulty in sucking, constipation, prolonged jaundice, myxedematous facies and macroglossia, abdominal distension with umbilical hernia and hypotonia. Slowed growth and delayed psychomotor development are usually apparent around 4 to 6 months. Without treatment, the disease causes severe intellectual disability.
The neonatal screening is based on a primary TSH and/or thyroxine (T4) assay. Depending on the countries or geographies, three screening strategies exist:
Although each approach detects the majority of infants with primary congenital hypothyroidism, the initial TSH assay is now the preferred strategy for the majority of screening programs. Infants with subclinical hypothyroidism (high blood TSH, normal T4) are more reliably detected by an initial TSH assay, while central hypothyroidism is only detected favorably by an initial T4 assay.
After screening, confirmation of congenital hypothyroidism is based on detection of elevated serum TSH and more or less collapsed T4 (or free T4). Additional tests (scintigraphy, CT scan, and thyroid ultrasound, a serum thyroglobulin assay) can identify the cause of congenital hypothyroidism and distinguish transient from permanent forms.
Levothyroxine is the treatment of choice. The recommended loading dose is 10 to 15 mg/kg/day. Serum TSH usually normalizes within 2 to 4 weeks. In early childhood, repeated TSH and T4 testing controls are essential to ensure optimal neurocognitive outcomes.
The etiological diagnosis (EI. Primary or secondary hypothyroidism, dysgenesis or dyshormonogenesis) is not necessary to initiate treatment with replacement hormones. If it is not a transient form, treatment should be continued throughout the life of the individual.
Thyroid dysgenesis is generally considered sporadic. There is therefore no risk of recurrence for a subsequent pregnancy.
Thyroid dyshormonogenesis is autosomal recessive. The risk of having a sibling with the same disease is then 25%.
There is a risk of recurrence of transient congenital hypothyroidism in newborns of mothers with autoimmune thyroid disease associated with antibody blocking thyrotropin receptors (TRB-Ab).
The NEONATAL TSH Screening ELISA kit is an ELISA-type quantitative test for quantifying thyrotropin or thyroid stimulating hormone (TSH) from dried blood lab test samples on 903® or 226 blotting paper. This TSH test is for newborn baby screening for congenital hypothyroidism.
The NEONATAL TOTAL-T4 Screening ELISA kit is an ELISA-type quantitative hypothyroidism test used to quantify the totality of thyroxine (T4) contained in a test dried blood samples on 903® or 226 blotting paper. This test is for congenital hypothyroidism newborn screening.
