The future of prenatal cytogenetic diagnostics: a personal perspective

Prenatal cytogenetic diagnosis: results obtained in the specialized laboratory of Clínica Universitaria Colombia from 2013 to 2019

OBJECTIVE

Prenatal cytogenetic evaluation is a key tool for identifying alterations in pregnant women with high risk for fetal chromosomal abnormalities (CA). In Colombia, there are not large-scale reports about the prevalence and pattern of CA in prenatal cytogenetic analysis.

METHOD

A descriptive study was performed from registers of prenatal cytogenetic analysis on amniotic fluid (AF), chorionic villus biopsy (CVS), and fetal blood (FB) samples sent to the specialized laboratory of the Clínica Universitaria Colombia between 2013 and 2019.

RESULTS

The prevalence of CA was 20.9%. The trisomies 21, 18, 13, and monosomy X were the most frequent aneuploidies, and the derivative chromosomes were the most frequent structural abnormalities. Although the rate of CA was higher in women over the age of 35 years old; monosomy X, unbalanced rearrangements, and microduplications were associated with the group of women under the age of 35 (p < .05). Trisomies 21 and 18 were the most common aneuploidies identified by FISH and were found to be altered in 52% of the aCGH studies. Ultrasonographic markers associated with CA were the most frequent clinical indication.

CONCLUSION

In Colombia, the invasive prenatal cytogenetic analysis continues being an important diagnostic tool available for pregnant women with high risk for fetal CA.

Molecular prenatal diagnosis: the impact of modern technologies

Originally prenatal diagnosis was confined to the diagnosis of metabolic disorders and depended on assaying enzyme levels in amniotic fluid. With the development of recombinant DNA technology, molecular diagnosis became possible for some genetic conditions late in the 1970s. Here we briefly review the history of molecular prenatal diagnostic testing, using Duchenne muscular dystrophy as an example, and describe how over the last 30 years we have moved from offering testing to a few affected individuals using techniques, such as Southern blotting to identify deletions, to more rapid and accurate PCR-based testing which identifies the precise change in dystrophin for a greater number of families. We discuss the potential for safer, earlier prenatal genetic diagnosis using cell free fetal DNA in maternal blood before concluding by speculating on how more recent techniques, such as next generation sequencing, might further impact on the potential for molecular prenatal testing. Progress is not without its challenges, and as cytogenetics and molecular genetics begin to unite into one, we foresee the main challenge will not be in identifying the genetic change, but rather in interpreting its significance, particularly in the prenatal setting where we frequently have no phenotype on which to base interpretation.