[Cytogenetic findings in patients with Down's syndrome]

In order to describe the frequency of non classical forms of 21 trisomy in patients with Down's syndrome at the cytogenetic's laboratory of our institution (Instituto de Nutrición y Tecnología de los Alimentos, Universidad de Chile) 201 chromosomal studies from peripheral blood lymphocytes of patients referred with a clinical diagnosis of Down's syndrome were analyzed. Among them 22 (11%) cases showed no chromosomal abnormalities, 161 (80%) had classic 21 trisomy, 7 (3.5%), showed 21 trisomy by translocation, 5 (2.5%) had 21 trisomy mosaicism, 6 (3%) showed 21 trisomy plus an autosomic balanced translocation. Male to female rate was 1.18:1 and diagnosis was done at the neonatal period in 26.8% of cases. Early recognition of the different kinds of chromosomal abnormalities in Down's syndrome is important if appropriate genetic council is the goal.