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 thyroid gland. 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 cases of 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 mechanisms in pathogenesis of these conditions. The development of thyroid gland is controlled by expressed transcription factors and genes participation in the control of hormonogenesis. Mutation of these genes may therefore follow to disorders in the development of thyroid 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 also during the development of other organs, which may be affected in the same way as thyroid gland (e.g. cleft palate and epiglottis in the mutation of gene for TTF-2,malformation of the kidneys in mutations of gene for PAX-8, lung and neurological disorders in mutation of gene for TTF-1, disorders in hearing, extension of vestibular aqueduct and struma (goiter) inmutation of PDS gene fro DFNB4). At the present time extensive research is devoted to other candidate genes. The syndrome of thyroid gland disorder is defined at various levels - from the disorder of iodine organification (Pendered syndrome, Hollander syndrome) and/or disorders in the synthesis (heterotopy) (Hollander et al. 1966, Pendred 1896).

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