All issues > Volume 33(7); 1990

Original Article

J Korean Pediatr Soc. 1990;33(7):1004-1008. Published online July 31, 1990.

A Case of (21q 21q) Translocation Down Syndrome Inherited from a t(21q 21q) Balanced Carrier Mother.

Byeong Gie Yeo¹, Chong Woo Bae¹, Yong Mook Choi¹, Chang Il Ahn¹, Bo Hoon Oh²

¹Department of Pediatrics, College of Medicine, Kyung Hee University, Seoul, Korea
²Department of Obstetrics & Gynecology, College of Medicine, Kyung Hee University, Seoul, Korea

Received: December 28, 1989;  Accepted: March 21, 1990.

Abstract

Vast majority of t(21q 21q) Down syndrome occur de novo and familial cases are extremely rare. In familial translocation Down syndrome, One of the parent show 45 chromosomes. In general, the carrier parent carrying (21q 21q) translocation is phenotypically normal because significant amount of genetic material has not been lost in the translocation process. Homologous Robertsonian translocation can be produced either by abnormal gametogenesis or by postzygotic mistake in mitosis soon after fertilization. The incidence of t (21q 21q) balanced carrier in general population is 1 in 2 — 2.5 million live birth. In homologous Robertsonian translocation, the risk of producing abnormal offspring is 100%. Therefore, this carrier mother should be informed about sterilization. In the present case, chromosomal study of mother showing normal female phenotype revealed balanced (21q 21q) translocation carrier with a karyotype 45, XX, —21, —21, +t (21q 21q) and chromosomal study of patient revealed (21q 21q) translocation down syndrome with a karyotype 46, XY, -21, +t (21q 21q). Thus, it is important to perform maternal chromosome study in case of translocation down syndrome and genetic counselling of this pedigree to prevent producing repetitive abnormal off- springs. In addition to case report, we present a brief review of the related literatures.

Keywords :Down syndrome, Translocation, Chromosome anomaly