Prenatal Diagnosis of Extrastructurally Abnormal Chromosomes: Clinical Experience and Literature Review

Background: To evaluate the clinical association of extrastructurally abnormal chromosomes (ESACs) with pregnancy outcome based on the cytogenetic characteristics of the ESACs. Methods: We retrospectively reviewed 12 ESAC cases identified from 12,991 cases who received genetic amniocentesis between January 1983 and March 2008. Prenatal ultrasound findings, characteristics of ESACs (karyotypes, special features, origin, inheritance) and pregnancy outcomes were recorded. Results: The prenatal prevalence of ESACs was 0.092% (12/12,991). Of the 12 ESAC cases, all were de novo. Seven (58.3%) originated from nonacrocentric chromosomes and the other 5 (41.7%) were from acrocentric chromosomes, with 3 originating from chromosome 15. Six of the 12 cases (50%) were large ESACs; however, the other 6 (50%) were medium to small ESACs. All acrocentric ESACs contained dicentric and bisatellite characteristics. Using FISH and SKY techniques, the origins of 2 cases (patients 10 and 12) were clearly identified to be from chromosomes 15 and 10, respectively. Five of the 12 ESAC cases (41.7%) had congenital anomalies found by prenatal ultrasound. All were nonacrocentric in origin that were medium (1/5) to large (4/5) in size. After prenatal genetic counseling, 8 of the 12 (66.7%) couples opted to terminate the pregnancy. The other 4 (33.3%) continued the pregnancy and their babies were delivered at term normally and were followed-up, with normal development ranging from 2 to 17 years. Conclusion: With sophisticated cytogenetic characterization and ultrasound examination, it is possible to precisely categorize most fetuses with ESACs as being either at high risk of abnormality or at a relatively low risk. [J Chin Med Assoc 2009;72(1):29-33]