Early Developmental Stage Correction of Chromosomal Abnormalities

A few weeks ago an article appeared online on medicaldaily.com with the title: Genetic Testing Sometimes Finds Chromosomal Abnormalities In Embryos, But They May Turn Normal Before Birth. This article as written appears to give a false impression that chromosome abnormalities diagnosed prenatally may correct themselves before birth.

Dr. Iosif Lurie, medical geneticist and CDO Medical Advisor offers his comments.

Recent data (especially after invention of molecular methods in cytogenetics) shows that at the early stages of development a cell may attempt to correct some cytogenetic anomalies. Trisomic cells may “evict” the additional chromosome, cells with a structural anomaly in one chromosome may use either the same “expulsion” tactics or another rescue mechanism involving many chromosomes (chromothripsis). However, these mechanisms may be successful only at the earliest stages (maybe in the first 1-2 weeks after fertilization), and definitely before any prenatal diagnosis. A fetus at 9-10 weeks already has the same chromosomal complement as he/she will have after birth.

Moreover, sometimes a cell having, for example, two identical maternal chromosomes and one paternal expels the paternal one. A chromosomally normal embryo (child) will result but with uniparental disomy. And if this chromosome has a recessive gene this gene will be homozygous in the child. I think that rare cases of UPD5, for example, are results of such rescues at the early stages of development.

After an unfavorable prenatal diagnosis should parents decide to terminate a pregnancy, most centers will confirm the prenatal diagnosis by pathologic and/or cytogenetic examination of the fetus. Should numerous cases of a chromosomally normal fetus being mistakenly aborted after an erroneous diagnosis of chromosomal pathology we would correspondingly expect to see an increase in “wrongful death” litigation. And we have not seen this.

This article gives a false impression that in many cases chromosomal abnormalities revealed by prenatal diagnosis may be restored by themselves. This underscores the importance of always checking with your personal healthcare provider about any information you locate online or elsewhere, it may not always be complete or accurate.

Dr. Iosif Lurie, Medical Geneticist
Linda Sorg, CDO President