Recently recognized genetical background of a few disease unit in the horses was reviewed in presented paper. The identification of these disorders was possible to great extent due to the improvement had been done in studies on equine gene mapping. A molecular basis of the following diseases were discussed: hypercalaemic periodic paralysis (HYPP), severe combined immunodeficiency (SCID) and overo lethal white syndrome (OLWS). Preliminary studies on the reasons of such disorders like: exertional rhabdomyolisis (ER), summer dermatitis and chronic obstructive pulmonary disease (COPD) were also presented.