ATAXIC GAIT AND MENTAL-RETARDATION WITH ABSENCE OF THE PATERNAL CHROMOSOME-8 AND AN IDIC(8)(P23.3) - IMPRINTING EFFECT OR NULLISOMY FOR DISTAL 8P GENES

A female child with mild dysmorphisms, motor and mental retardation ha d a 45,XX,-8,-8,+psu dic(8)(p23.3) karyotype in blood lymphocytes, ski n fibroblasts and in a lymphoblastoid cell line. DNA analysis showed t hat the proposita was nullisomic for the 8pter region distal to D8S264 , at less than 1 cM from the telomere. Analysis of DNA polymorphisms o f 38 loci spread along the entire chromosome 8 revealed that only mate rnal alleles were present, distributed in four heterozygous and four h omozygous regions. This finding indicated that the rearrangement occur red during maternal meiosis in a chromosome recombinant with a minimum of seven crossovers. To our knowledge this is the first case of unipa rental maternal disomy for chromosome 8 and of nullisomy for the dista l 1-cM portion of the short arm. The available data are in favour of t he assumption that no imprinted genes are present on chromosome 8. Thu s, dysmorphisms, motor and mental retardation of the proposita are lik ely to be caused by the nullisomy for the region distal to D8S264, a r egion in which a recessive gene for epilepsy with progressive mental r etardation is known to be located.