Page 11 - 2021 Winter CMTA Report

increased. An abnormal result is then performing a biopsy of the detect the presence of the spe-
usually followed by more defini- embryo to remove a small num- cific mutation gene: Two copies
tive testing (amniocentesis or ber of cells that can then be indicate an affected embryo; one
chorionic villous sampling). tested. Typically, an embryo is copy would identify embryos
grown (incubated) in a labora- destined to become genetic carri-
PREIMPLANTATION tory for five days after ers of CF and those without
GENETIC TESTING fertilization. A 5-day-old embryo probe activity would be consid-
Since 1974, IVF has been used (blastocyst) has an inner cell ered unaffected.
to help millions of couples who mass—which is destined to To illustrate, a prospective
were unable to conceive for a become the baby—and an outer mother is tested for cystic fibro-
variety of reasons: blocked cell mass (trophectoderm) that sis and found to be a silent
Fallopian tubes, issues with will ultimately develop into the carrier of a CF mutation. Her
ovulation or sperm production placenta and amnion. Using an partner is then tested and is also
and endometriosis, to name a incredibly small and precise a carrier of a CF mutation. There
few. It is estimated that over laser, a small opening is made in is a 25 percent chance of having
8 million babies have been con- the wall of the embryo and cells a baby with cystic fibrosis, which
ceived via IVF since Louise are removed from the trophecto- affects multiple organs—particu-
Brown—the first IVF success— derm. The embryo is then frozen larly the lungs. Incredible
was born in 1974. while the cells are tested. advances in treatments have
The advent of preimplanta- PGT-A tests the cells for an been made and, armed with this
tion genetic testing (PGT) has abnormal number or pairing of knowledge, the couple may elect
added another group of prospec- chromosomes (aneuploidy). to proceed with conceiving on
tive parents: those who have Selecting embryos with a normal their own. They could also
family or personal histories of number and arrangement of decide to conceive using an egg
genetically inherited conditions chromosomes (euploid) to trans- or sperm from a donor who does
or who are at a higher risk of fer back to the patient not carry the CF mutation. They
chromosomal anomalies due to significantly increases the might choose to adopt. They can
advanced maternal age or recur- chances of a healthy pregnancy. also elect to have IVF and test
rent unexplained pregnancy PGT-M refers to testing the their embryos for cystic fibrosis.
losses. embryos for single-gene muta- PGT-M is now widely
PGT refers to the process of tions like the one that causes CF. utilized to identify embryos
creating embryos via IVF and A probe is created that can (continued on page 13)

WINTER 2021 THE CMTA REPORT 11