A cytogenetic investigation on the Lethal White Syndrome in sheep

The mating of genetically related animals is known toincrease the homozygosity. Such condition can alsoincrease the chances of the offsprings to be affected byrecessive traits. Lethal white syndrome (LWS), is anautosomal genetic disorder most prevalent in the AmericanPaint Horse. Affected animals phenotypically appearnormal, although they have all-white coats and blueeyes. Internally, they have a non-functioning colon anddie within a few days after birth.In a small group of Cameroon sheep, where only oneram was used for several consecutive years and matedto his relatives, five lambs were completely whitecoatedwith blue eyes. All died shortly after birth. Acytogenetic investigation was carried out on the availablemothers, most probably heterozygous carriersof the genetic defect. Peripheral blood sample cultureswere performed for two ewes to get bothnormal and BrdU-treated cultures, the latter toobtain R-banded preparations. Normal cultureswere used to perform CBA-banding and FISHtechnique,while R-banded preparations were usedfor both karyotyping (RBA-banding) and RBPIFISHtechnique.The analysis of the CBA- and RBA-banding patternshowed karyologically normal arrangement(2n054,XX). LWS syndrome has been comparedto Hirschsprung's disease in humans, which iscaused by mutations on the EDNRB gene. A conventionalFISH analysis carried out by using aBAC probe, showed EDNRB gene deletion at heterozygousstatus. A RBPI-FISH experiment wasadditionally performed to clarify the position ofthe gene along the chromosome. According tostandard ideogram, the EDNRB gene was confirmedto be located on the OAR10q2.2. Thisfinding confirmed that the ewes were heterozygouscarriers of EDNRB gene deletion.