Autosomal Chromosome Aberrations

Abstract

Prior to the introduction of cytogenetic techniques in human medicine some 15 years ago, only a single chromosome aberration syndrome, Down’s syndrome, was known clinically, but its etiology was still unclear. By direct chromosome examination, it was later shown that the clinical picture of Down’s syndrome is caused by the presence of an additional No. 21 chromosome, and a large number of other autosomal chromosome aberrations was also detected. With an increasing number of cases with the identical karyotype abnormality, it became evident that most, if not all, autosomal chromosome aberrations cause a rather distinct malformation syndrome. Moreover, newly developed staining techniques which reveal specific banding patterns along the chromosomes allowed a clear identification of every particular chromosome and a better assessment of the amount and the localization of the chromosome material present in the trisomic or monosomic state. Fig. 1 shows the bands revealed by Quinacrine fluorescence and Giemsa staining techniques (Q and G-bands) as defined and numbered at the Paris Conference (1971). Fig. 2 presents a karyotype with a balanced translocation between chromosomes 15 and 18 with the breakpoints at bands 15q26 and 18q21: 46,XY,t (15;18) (q26;q21) (Schinzel et al., 1975a).