Preimplantation genetic diagnosis, or PGD, is regarded as critical among parents who are diagnosed with genetic disorders or have a history of inherited diseases. PGD testing decreases the chances of embryos with genetic defects being implanted in the IVF female. This is a major improvement over conventional genetic testing methods like amniocentesis, which can be used only when pregnancy has initiated. PGD helps in the identification of healthier embryos, free of genetic defects like chromosomal disorders.
Chromosomes are the carriers of genetic information. Females have two X chromosomes. Males have one X and one Y chromosome. These chromosomes are present in the male sperm and female egg. The embryo contains a combination of 46 chromosomes. Normal human cells are supposed to contain 46 chromosomes, present in 23 pairs.
Chromosomal disorders refer a genetic anomaly wherein the structure, arrangement or number of chromosomes is different from the norm. Chromosomal disorders can be present in various forms and this includes abnormal deletions of chromosomes, inversions and translocations.
PGD Chromosomal Testing: FISH
For detecting such chromosomal disorders, PGD testing uses tests like Fluorescent In Situ Hybridization, or FISH. This is among the most advanced of pre-conception testing methods that can quickly decipher chromosomally-unstable embryos. FISH test results can also help the IVF parents in understanding the reason for their previous miscarriages, i.e., the typical chromosomal disorders that have led to repeated termination of embryos.
PGD's Use in Detecting Aneuploidy
PGD tests have also helped to decode chromosomal disorders of aneuploidy. This refers to a type of chromosome irregularity where there are too many or very few chromosomes. The most common genetic disorders of aneuploidy that are effectively decoded through PGD include Down's syndrome or trisomy 21, which is chromosomal aneuploidy of chromosome 21 (extra chromosome). Other examples of such chromosomal disorders include Trisomy 13 and 18. Chromosomal aneuploidy gives rise to some rare syndromes such as Klinefelter Syndrome and Turner Syndrome, which can be detected with PGD. Chromosomal aneuploidies detected through PGD that are responsible for early miscarriages include the presence of an extra chromosome in chromosomes 15, 16 and 22.