Theoretical basis and application of molecular diagnostics.

Molecular biology has brought much progress in understanding physiology and pathophysiology as well as tumor development in thyroidology. The principles of gene organisation, regulation, and expression will be mentioned in regard to the thyroid and thyroid hormones. A growing number of thyroid disorders are linked to molecular events like mutations, deletions, splice errors, gene duplications or aberrant expression. The genetic causes and molecular approaches in diagnosis are most evident in rare inheritable syndromes, such as familial medullary thyroid carcinoma (FMTC, MEN 2), thyroid hormone resistance or non-autoimmune autosomal dominant hyperthyroidism. Furthermore, in toxic nodules, papillary and sporadic medullary thyroid carcinomas somatic mutations have been found, of which the pathogenetic role is still under debate. The molecular tools to diagnose gene mutations are mostly based on the polymerase chain reaction (PCR). Screening methods include single-strand conformation polymorphism (SSCP), denaturing gradient gel electrophoresis (DGGE), and temperature gradient gel electrophoresis (TGGE). More specific methods like enzyme restrictions or allele-specific PCR require precise knowledge of the mutation which is searched for in genomic DNA. DNA sequencing is the safest but not the cheapest or simplest way to detect a mutation. Some examples will be given for the application of the above mentioned methods in diagnosing certain thyroid diseases.