Estudo da origem do cromossomo 21 extra em portadores de Síndrome de Down

Abstract

Down syndrome is usually due to meiotic nondisjunction leading to trisomy 21.The origin of nondisjunction in trisomy 21 has so far been studied using cytogenetic heteromorphisms and DNA polymorphisms. Short sequence repeats have recently been described as an abundant class of DNA polymorphisms in the human genome, which can be typed using the Polymerase Chain Reaction (PCR) amplification. Analysis of these polymorphisms may provide a more accurate understanding of the meiotic stage of nondisjunction in trisomy 21 than that previously provided by chromosomal heteromorphisms. The following DNA polymorphisms located in pericentromeric region of human chromosome 21. Were typed D21S13E, D21S16 and D21S120. The other polymorphism studied was HMG14-GT2 which map to the terminal band 21q22.3. In the present stud such markers were used in order to the determine the parental origin and the meiotic stage of the additional chromosome 21 in 32 cases of Down syndromy. Seven families were informative showing that nondisjunction ocurred in meiosis I and three were from maternal origin using HMG14-GT2 polymorphism. In the other molecular systems the families are not informatives.