FAMILIAL TRANSMISSION OF A DELETION OF CHROMOSOME-21 DERIVED FROM A TRANSLOCATION BETWEEN CHROMOSOME-21 AND AN INVERTED CHROMOSOME-22

Chromosome analysis of a newborn boy with Down syndrome resulted in th e identification of a family with an unusual derivative chromosome 22, The child has 46 chromosomes, including two chromosomes 21, one norma l chromosome 22, and a derivative chromosome 22, Giemsa banding and fl uorescent in situ hybridization (FISH) studies show that the derivativ e chromosome is chromosome 22 with evidence of both paracentric and pe ricentric inversions, joined to the long arm of chromosome 21 from 21q 21.2 to qter, The rearrangement results in partial trisomy 21 extendin g from 21q21.2 to 21q terminus in the patient. The child's mother, bro ther, maternal aunt, and maternal grandmother are all carriers of the derivative chromosome, All have 45 chromosomes, with one normal chromo some 21, one normal chromosome 22, and the derivative chromosome 22, T he rearrangement results in the absence of the short arm, the centrome re, and the proximal long arm of chromosome 21 (del alpter-21q21.2) in carriers, Carriers of the derivative chromosome in this family have n ormal physical appearance, mild learning disabilities and poor social adjustment. Am. J. Med. Genet. 70:399-403, 1997. (C) 1997 Wiley-Liss, Inc.