Developmental Defects of the Thyroid Gland: Relationship with Advanced Maternal Age

In tro duc ti on Developmental defects of the thyroid gland, including aplasia (absent gland), hypoplasia (small gland) and ectopia (unusual location) are collectively referred to as thyroid dysgenesis (TD) (1). In iodine sufficient countries, 85 % of permanent congenital hypothyroidism (CH) is due to TD (2). Most cases of TD are sporadic and their pathogenesis remains unknown (3). Defects in embryogenesis, migration, differentiation or growth of the thyroid gland during organogenesis may lead to CH (4). Most CH patients with TD have a defect in thyroid migration resulting in ectopic thyroid tissue located in the lingual, suprahyoid or infrahyoid regions (4,5). The ectopic gland is often asymptomatic but may cause local symptoms (6). The second most common variant of TD is absence of detectable thyroid follicular cells, a condition commonly called agenesis