Abstract
The first association of a chromosomal anomaly (trisomy of chromo- some 21) with a pathological phenotype (Down syndrome) was discovered more than 50 years ago. Since that time clinical genetics itself has changed a great deal.
Today we know of many numerical and structural abnormalities of the human karyotype, which are causal for different clinical syndromes. However- not each of the chromosomal abnormalities is believed to be pathological.
Today we know a number of so called heteromorphisms - variants of the human karyotype that do not affect the phenotype of their carriers. Nearly all of these variants are inherited from one of the parents.
The chromosomes with the areas of constitutive heterochromatin (1, 9, 16 and Y) and acrocentric chromosomes (13, 14, 15, 21 and 22) are commonly involved. Although these findings are neither uncommon nor clinically significant, the interpretation of the findings by cytogeneticists and clinical geneticists can be sometimes difficult.
Also - whenever there is a complete cytogenetic formula "including the variant" in the clinical report provided to the patient, it is necessary to inform the patient very clearly about the benign character of this finding in order to prevent unnecessary anxiousness