Disorders in the Development of Thyroid Gland: Survey of Present Knowledge

Overview

Clinical aspects enable to differentiate genetically based disorders of development, disorders of organogenesis,and other causes (caused by external influence - teratogenic disorders of development).Heterotopia, athyreosis and hypoplasia are the most frequent forms of disorders in the development of thyroidgland. These developmental disorders are most frequently connected with decreased function of thyroid gland,hypothyreosis, in 80-85%. Dysgenesis of thyroid gland is considered as a disease of sporadic incidence. The casesof familial dysgenesis having been reported so far, increased incidence of inborn combined developmental defects,affecting more frequently females, and racial differences in incidence draw attention to genetically-based mechanismsin pathogenesis of these conditions.The development of thyroid gland is controlled by expressed transcription factors and genes participation inthe control of hormonogenesis. Mutation of these genes may therefore follow to disorders in the development ofthyroid gland at different levels. Mutations of the genes for TTF-1, TTF-2, PAX-8, but also DFNB4 (PDS gene)have been proved in some patients with dysgenesis of thyroid gland. These transcription factors are expressed alsoduring the development of other organs, which may be affected in the same way as thyroid gland (e.g. cleft palateand epiglottis in the mutation of gene for TTF-2,malformation of the kidneys in mutations of gene for PAX-8, lungand neurological disorders in mutation of gene for TTF-1, disorders in hearing, extension of vestibular aqueductand struma (goiter) inmutation of PDS gene fro DFNB4). At the present time extensive research is devoted to othercandidate genes. The syndrome of thyroid gland disorder is defined at various levels - from the disorder of iodineorganification (Pendered syndrome, Hollander syndrome) and/or disorders in the synthesis (heterotopy) (Hollanderet al. 1966, Pendred 1896).

Key words:
disorders of thyroid gland development, dysgenesis, molecular biology