Malattie congenite del sistema nervoso del bovino

Bovine congenital diseases of thenervous system In calves, congenital (condition existing at or before birth) dis-orders of the nervous system are not rare: in the past they wereestimated to account for about 20% of all congenital defects.Unfortunately, the scarcity of surveillance programs and thelow economical value of young animals hinder submission ofclinical cases to diagnostic centers; hence their real prevalencegoes underestimated. Moreover, many defects can be identi-fied only by necropsy or histopathology.Congenital neurological conditions may be due to external ter-atogens or to genetic defects.Teratogens are biologic, toxic, chemical, physical or metabol-ic and can act directly on the developmental processes or canalter patterns of gene expression, inhibit cell interactions, orblock morphogenetic cell movements. Genetic defects are most-ly represented by autosomal inherited recessives and are usu-ally based on inborn errors of metabolism and on lack or dys-function of hormones, receptors, enzymes, structural proteins,neurotransmitters and ion channels (metabolic defects, stor-age defects, disturbed neurotransmission, channelopathies). Theincreased use of intensive breeding programs, based on the wide-spread use of selected elite sires, and the consequent increaseof the “inbreeding grade”, has allowed the homozygous pres-ence of recessive variants - responsible for malformation - inthe inbred progeny of many breeds.Genetic causes includes also «de novo» pathogenic variants thatmay occur in one of the germ cells (sperm or egg) of one ofthe parents, or arise in the fertilized egg itself during early em-bryogenesis.The defects characterized by structural deformities of the nerv-ous structures are termed “congenital malformation” and arethe result of disorders of tissue development such as: agene-sis (complete absence of an organ), aplasia (absence of an or-gan with retention of the organ rudiment), hypoplasia (in-complete development of an organ), dysraphic anomaly (fail-ure of opposed structures to undergo adhesion and fusion), in-volution failure (persistence of an embryonic structure that nor-mally disappears during development), division failure (in-complete cleavage of embryonic tissues owing to lack of pro-grammed cell death), atresia (failure of an organ rudiment toform a lumen), dysplasia (abnormal organization of cells in atissue), ectopia (error of morphogenesis in which an organ islocated outside its correct anatomic site), dystopia (error of mor-phogenesis in which an organ is retained at a site where it residedduring a stage of development). The majority of these disor-ders involve also the nervous system. The defect characterized by inborn alteration of physiologicalfunctions or metabolic processes may not be expressed or rec-ognized until later in life, so being erroneously interpreted asacquired diseases.The article presents the most common congenital defects of thenervous system in calves. Due to the fact that for the majori-ty of the congenital diseases the exact cause remains unknown,it is intention of this article to prompt farmers and veterinar-ians to consider - whenever possible - the submission of suchcases to diagnostic centers for further studies and investigation.