Résumé
The ACLF provides laboratories since 2005 with external quality assessments for the caryotype (including FISH) and array-CGH. More than 70 laboratories in constitutional cytogenetics, hematology and array-CGH participate each year. The evolution of our practices requires continuously adaptation but these EQAs and their European equivalents have made us aware of the state of knowledge and certain limitations reveal the loss of competence in classical cytogenetic analysis as well as of molecular pangenomic techniques. Indeed we have identified technical gaps or pitfalls that we will illustrate with 2 examples. Postnatal Cytogenetics: We proposed a pericentric chromosome 5 inversion inv(5)(p13q13) considered a variant in the literature. A large discrepancy was observed between laboratories reporting this chromosome a polymorphism and others reasoning as a classic pericentric inversion. The "youngest" cytogeneticists have lost experience regarding a variant not recently reported in the literature. Postnatal Array-CGH: The second proposed case involved a caryotype-validated pentasomy X. Surprisingy some laboratories missed the pentasomy. They concluded a trisomy or tetrasomy mosaicism. The explanation may lie in the limitations of the assessment of the copy number by algorithms used in the presence of unusual ratios especially at the level of gonosomes, a too fast analysis or a technique that did not allow to evaluate a large number of chromosome X copies. This exercise allowed us to observe the limitations of certain computational algorithms and remind us of the importance of maintaining a solid formation in classical cytogenetic analysis to best interpret the results from pangenomic molecular techniques (array-CGH, WGS/WES).