Complex de novo cryptic subtelomeric rearrangements in a fetus with multiple ultrasonographic abnormalities and a normal karyotype at amniocentesis.

Objective: Prenatal diagnosis is usually offered to the majority of pregnancies with fetal structural abnormalities detected by prenatal ultrasound; however, only a small proportion show an abnormal karyotype. We wanted to detect cryptic subtelomeric rearrangements (CSTR) in a fetus with multiple abnormal ultrasonographic findings that revealed a normal karyotype at amniocentesis.

Methods: Fetal chromosome analysis was performed from amniotic fluid cells. Parental chromosome analysis was done on PHA stimulated lymphocyte cultures. For fluorescence in situ hybridization (FISH) analysis, ToTelVysion multicolor DNA probe mixture was used to hybridize the p and q telomeres of each chromosome.

Results: The amniotic fluid chromosome analysis revealed an apparently normal 46,XY karyotype. A follow-up FISH analysis showed three apparently balanced complex translocations involving (1) the chromosome 4p and 22q telomeres (2) 4q and 11q telomeres and (3) 8p, 20p and 20q telomeres. Parental chromosome and subtelomere FISH analysis was found to be normal.

Conclusion: To our knowledge, this is the first report of complex de novo cryptic translocations in an abnormal fetus. These CSTR identified by FISH with subtelomere-specific probes are not detected by other cytogenetic and/or molecular cytogenetic approaches. However, to confirm the balanced nature of CSTR, array-CGH can be helpful. Further studies are in progress to determine the frequency of CSTR and its significance in the etiology of fetal abnormalities.