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Primary thyroid failure present at birth
- Increasing trend in the United States
- Unclear etiology (definitional issues related to newborn screening vs. true increase from unidentified risk factors)
- Had been 1 in 3,000–4,000 births, United States and worldwide
- In 2007, U.S. incidence 1 in 2,370 births
- Male-to-female ratio is 1:2–1:3.
- 80% dysgenesis or agenesis; 20% dyshormonogenesis
- Racial differences: prevalence in African American infants ∼1/3 that in whites
- Higher prevalence of congenital hypothyroidism in low-birth-weight (>2,000 g) and macrosomic (≥4,500 g) babies
- Dysgenesis is usually sporadic.
- Familial occurrence in 2%
- Mutations have been found in the TSH-receptor gene and in the transcription factors PAX-8, TTF-1, and TTF-2 (FOXE1).
- Dyshormonogenesis is inherited in an autosomal recessive pattern. Most commonly
- Chromosome 2p: Mutations in the thyroid peroxidase gene result in partial or complete loss of iodide organification.
- Chromosome 19p: Mutations in the sodium-iodide symporter gene result in an inability to maintain the normal thyroid-to-plasma iodine concentration difference.
- Pendred syndrome (chromosome 7q): Mutations in PDS gene cause the most common syndromal form of deafness; a mild organification defect leads to goiter, usually in childhood.
- Thyroid gland malformation
- Agenesis: absent thyroid gland
- Dysgenesis: ectopic (e.g., sublingual) or incorrectly formed (e.g., hemigland) thyroid
- 15 known defects of thyroxine (T4) synthesis, including those in iodide transport and iodide organification
- Transient hypothyroidism
- Maternal ingestion of antithyroid drugs
- Transplacental transfer of maternal antithyroid antibodies (transient or permanent damage)
- Exposure to high levels of iodine-povidone, (i.e., Pyodine, Betadine) in neonatal period
Commonly Associated Conditions
- Down syndrome neonates have lower T4 (left-shifted normal distribution) and mildly elevated TSH, suggesting a mild hypothyroid state.
- Newborns with congenital hypothyroidism have an increased risk for congenital heart defects, and vice versa (common embryologic developmental program).
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