Thyroid Hemiagenesis: Incidence, Clinical Significance, and Genetic Background

Abstract

Patients with THA are prone to develop additional thyroid pathologies and theoretically might benefit from l-thyroxine treatment to lower the thyrotropin levels to those observed in the normal population. However, further research should be done to ascertain whether such intervention early in life would prevent development of associated thyroid conditions. At least, increased vigilance should be maintained to reveal all of the concomitant disorders as soon as possible during follow-up examinations. Application of high-throughput technologies enabling a genome-wide search for novel factors involved in thyroid embryogenesis might be the next step to expand the knowledge on THA pathogenesis.

Thyroid Hemiagenesis in a Thyroiditis Prone Mouse Strain

“…Thyroid hemiagenesis had not been noted by colleagues with extensive experience using NOD.H2 h4 mice (personal communication) or by ourselves in 11 other mouse strains, including 5 commonly used strains (BALB/c, C56BL/6, DBA/2, and AKR/N). Unlike most other strains, NOD.H2 h4 mice seem to be predisposed to developing thyroid hemiagenesis, consistent with the familial predisposition observed in some humans [3,38].…”

“…In addition, it is unlikely that the TSHR A-subunit transgene contributed to thyroid hemiagenesis in 1 mouse because (a) it occurred in 2 wild-type NOD.H2 h4 mice and (b) the transgene is located on chromosome 1 [17] and not on chromosomes 2, 12, 5, and 16, the locations of Pax 8, TTF1, Shh, and Tbx1. It should be emphasized that the genetic basis for thyroid hemiagenesis in humans could be identified in only a minority of cases with no common or specific gene identified [3,38], although thyroid autoimmunity was frequently present [39].…”

“…In an unusual case of Graves' disease, thyroid hemiagenesis was observed [4]. Individuals with thyroid hemiagenesis tended to develop other thyroid abnormalities but no common genetic basis was found for this condition [3].…”

“…The prevalence of thyroid hemiagenesis was 0.05% in 24,032 school children in Sicily [2] and 0.02% in 299,908 children and young adults in a normal Japanese population [1]. In a recent meta-review, the prevalence was reported to vary from 0.05 to 0.5% [3]. There tended to be a bias toward the absence of the left lobe, especially in females, and sometimes enlargement of the single lobe [1,2].…”

Analysis of the Seasonality of Births in a Large Cohort of Patients with Thyroid Hemiagenesis - A Preliminary Study

“…Thyroid hemiagenesis (THA) is a rare congenital developmental abnormality, where one of the thyroid lobes fails to develop (1). The etiology of THA and other thyroid dysgenesis (TD) is largely unknown (2,3).…”