TRISOMY-8 SYNDROME OWING TO ISODICENTRIC 8P CHROMOSOMES - REGIONAL ASSIGNMENT OF A PRESUMPTIVE GENE INVOLVED IN CORPUS-CALLOSUM DEVELOPMENT

Two patients with trisomy 8 syndrome owing to an isodicentric 8p;8p ch romosome are described. Case 1 had a 46,XX/46,XX, -8, +idic(8)(p23) ka ryotype while case 2, a male, had the same abnormal karyotype without evidence of mosaicism. In situ hybridisation, performed in case 1, sho wed that the isochromosome was asymmetrical. Agenesis of the corpus ca llosum (ACC), which is a feature of trisomy 8 syndrome, was found in b oth patients. Although ACC is associated with aneuploidies for differe nt chromosomes, a review of published reports indicates that, when ass ociated with chromosome 8, this defect is the result of duplication of a gene located within 8p21-pter. Molecular analysis in one of our pat ients led us to exclude the distal 23 Mb of Sp from this ACC region.