Congenital Hypothyroidism (CH)
CH may be inherited or sporadic. Most cases are sporadic, meaning there is no family history of the disorder. The cause of some sporadic cases of CH is a de novo mutation in one copy of a gene. That is, the mutation was not present in either parent but was acquired later. In this case the inheritance is autosomal dominant as there is a 50% chance of the new mutation being passed on to each future child and causing disease in that child. CH may also have an autosomal recessive inheritance pattern where a mutation is present in both copies of the gene. Normally a person has two functional copies of each gene. Each parent of a newborn with autosomal recessive CH typically has one functional and one mutated gene and is considered a carrier. When both parents are carriers, the chance of each of their children inheriting two mutated genes, and therefore being affected by CH, is 25%. There is also a 50% chance that a child will be a carrier (like their parents) and 25% chance that they will have 2 copies of a normal gene.
Carriers of congenital hypothyroidism do not typically have symptoms.
Most babies with CH do not show symptoms at birth. This is why it is important to screen for CH at birth. If babies with CH do not receive treatment, they have lifelong intellectual disability and slow physical growth. With treatment, symptoms can be prevented. Some newborns with a positive screen will have something other than permanent CH. Premature infants may have thyroid hormone deficiency related to prematurity. Other causes of transient CH include iodine deficiency, maternal thyrotropin blocking antibodies, maternal intake of antithyroid drugs and maternal or neonatal iodine exposure.
- Incidence: The incidence of classic CH is 1 in 2,000 to 1 in 3,000. It affects more females than males.
- New York State Method of Screening: Screening for CH is accomplished by measuring TSH levels in dried blood spot specimens by immunoassay.
- Testing can be affected by: Specimens collected at less than 24 hours of age can cause a false positive result.
- Interpretation/reporting of data: Results are reported as screen negative, borderline elevated TSH or as a screen positive referral. A repeat dried blood spot specimen should be collected for a borderline result. Results of thyroid function testing will also be accepted for a borderline result, but a repeat specimen is preferred. When results of thyroid function testing are submitted, both TSH and T4 results should be submitted and must include, the date of collection, normal ranges and a clinical interpretation. For a referral, prompt consultation with a specialist is required.
- Referral to Specialty Care Center: Patients with a screen positive newborn screen for CH are referred to an Endocrinology Specialty Care Center for evaluation by an Endocrinologist trained in the diagnosis and treatment of CH. In order to close a case, the New York State Newborn Screening Program requires thyroid function testing data to be submitted (both TSH and T4 results should be submitted and must include, the date of collection, normal ranges and a clinical interpretation. In addition, if available, results of thyroid imaging tests should also be submitted).
Diagnostic testing may include measurement of thyroid stimulating hormone (TSH), total thyroxine (T4), free T4, and thyroxine-binding globulin (TBG). Treatment should not be started based on newborn screening results alone. Confirmatory testing is required. If clinical signs and symptoms suggest hypothyroidism, regardless of newborn screening results, serum free T4 and TSH determinations should be performed.
Treatment is daily supplementation with an oral thyroid replacement hormone. Lifelong treatment and dose adjustments are required. For some cases of CH, at three years of age, therapy is discontinued for a trial period to determine whether lifelong treatment is needed.
Initiation of prompt treatment will prevent symptoms and result in normal development.
Congenital hypothyroidism (CH) is an endocrine disorder of impaired thyroid function that affects infants from birth. The thyroid gland is located in the lower neck. In most cases of CH, the gland is missing (aplasia), small (hypoplasia) or abnormally located (ectopic). In other cases, the gland is present, but does not function correctly [i.e. there is a defect in thyroid hormone synthesis or secretion (dyshormonogenesis)]. Thyroid hormones, which are made in the thyroid gland, are essential for brain development in infancy and normal growth in childhood.