Genetics of primary Congenital Hypothyroidism: Three decades of discoveries and persisting etiological challenges

Primary congenital hypothyroidism (CH) is the most common neonatal endocrine disorder, and may be etiologically subdivided into thyroid dysgenesis (TD), referring to abnormal thyroid development, and dyshormonogenesis, where a defective thyroid hormone biosynthesis pathway results in inadequate hormone production despite a structurally intact gland. Delayed treatment of neonatal hypothyroidism may result in irreversible neurodevelopmental impairment; therefore, where available, CH screening programs facilitate prompt diagnosis. However, the molecular basis for CH remains unclear in the majority of cases. This review summarizes current understanding of the genetic etiologies underlying primary CH and associated phenotypes. Classical genetic causes are discussed in the context of their role in normal thyroid physiology. Genes recently reported to play a role in the pathogenesis of CH are discussed, and novel genomic mechanisms in CH are described.