Masked monosomy 7 in myelodysplastic syndromes is uncommon and of undetermined clinical significance

Masked monosomy 7, i.e. detected by FISH but not by conventional cytogenetics, has been reported in varying frequency in MDS. To establish the prevalence and possible clinical significance of the aberration, we studied the 123 previously karyotyped MDS patients using FISH and a DNA probe specific for chromosome 7. Metaphase cytogenetics revealed ten patients (8%) with monosomy 7 (6 RAEB and 4 RAEB-t). FISH confirmed this result and detected four more cases (4%) with masked monosomy 7 (3 RA and 1 RARS). Thus, masked monosomy 7 is less common than has been suggested, and does not seem to carry the same prognostic weight as monosomy 7 diagnosed by metaphase cytogenetics.