entitled ''Co-occurrence of Chromosome 22q11.2 Microdeletion and Trisomy 21 Mosaicism.'' We thank the authors for their informative remarks about this association, but would like to point out that we definitely do not recommend investigating for chromosome 22q11.2 microdeletion (del22q11.2) in all cases of chromosomal aneuploidy with accompanying conotruncal heart defect (CTHD) . It seems that took our suggestion to investigate this microdeletion in patients with ''particular'' conditions to mean that we recommend this for ''all patients'' with chromosomal mosaicism or aneuploidy who also have a CTHD.
The specific 2002 report contains our description of a patient with del22q11.2 and mosaic trisomy 21 . This patient had facial dysmorphism and CTHDs including tetralogy of Fallot with pulmonary atresia, confluent pulmonary arteries, a large left-sided ductus arteriosus, left aortic arch, aberrant right subclavian artery, and secundum atrial septal defect. Routine chromosomal analysis performed on blood lymphocytes showed 47,XXΓΎ21[2]/46,XX [98]. Two key clinical findings prompted us to test for del22q11.2 in this case: the patient had hypocalcemia (serum calcium 5.8 mg/dl) and CTHDs that are common in patients with del22q11.2. This specific cardiac defect is rare in patients with Down syndrome or trisomy 21 . Using fluorescence in situ hybridization (FISH) analysis with probes specific for chromosomes 21 and 22, we showed that the patient had both the mosaic karyotype 47,XXΓΎ21[15]/46,XX[85] and del22q11.2.
We agree with that occurrence of chromosomal or Mendelian syndromes and