Cytogenetic heteromorphisms: survey results and reporting practices of giemsa-band regions that we have pondered for years.

Context: Cytogenetic heteromorphisms (normal variants) pose diagnostic dilemmas. Common Giemsa-band heteromorphisms are not described in the literature, although Giemsa-banding is the method most frequently used in cytogenetic laboratories.

Objective: To summarize the responses from more than 200 cytogeneticists concerning the definition and reporting of cytogenetic heteromorphisms, to offer these responses as a reference for use in clinical interpretations, and to provide guidance for interpretation of newly defined molecular cytogenetic heteromorphisms.

Design: The Cytogenetics Resource Committee of the College of American Pathologists and the American College of Medical Genetics administered a proficiency testing survey in 1997 to 226 participant cytogenetic laboratories. Supplemental questions asked whether participants considered particular Giemsa-banded chromosomal features to be heteromorphisms and if these would be described in a cytogenetic clinical report.

Results: Responses were obtained from 99% of participants; 61% stated they would include selected heteromorphism data in a clinical report. More than 90% considered prominent short arms, large or double satellites, or increased stalk length on acrocentric chromosomes to be heteromorphisms; 24% to 36% stated that they would include these in a clinical report. Heterochromatic regions on chromosomes 1, 9, 16, and Y were considered heteromorphisms by 97% of participants, and 24% indicated they would report these findings. Pericentric inversions of chromosomes 1, 2, 3, 5, 9, 10, 16, and Y were considered heteromorphisms with more than 75% of respondents indicating they would report these findings.

Conclusions: Responses were not unanimous, but a clear consensus is presented describing which Giemsa-band regions were considered heteromorphisms and which would be reported.