Preimplantation Genetic Diagnosis
In addition to testing for single gene mutation abnormalities, preimplantation genetic diagnosis (PGD) is also used to detect a chromosomal abnormality when one partner has a balanced reciprocal translocation or a Robertsonian translocation.
Chromosomes are string-like structures located in the nucleus of cells. Chromosomes contain genes that are made of DNA. All of our genetic information is on our chromosomes. A translocation is a change in chromosome structure in which chromosomes are attached to each other or pieces of different chromosomes have been interchanged.
In simple translocations an end segment of one chromosome is transferred to an end of another chromosome. Translocations in which the middle of one chromosome is shifted to the middle of another one are complex rearrangements involving at least three breaks in the involved chromosome. When shifting of genetic information occurs it results in serious disorders such as Down’s Syndrome (Trisomy 21), which can be caused by a 14/21 translocation. Another serious disorder caused by translocation is Chronic Granulocytic Leukemia which can be caused by part of the long arm of chromosome 22 is translocated to the short arm of chromosome 9.
People with balanced translocations generally have no medical issues although some may predispose to reduced fertility. The problem with having a balanced translocation is that although the person having it is healthy, the egg or sperm of the person with the balanced translocation can have and unbalanced chromosome make up that leads to their embryo being unbalanced resulting in either failed implantation, miscarriage or a child with an extra chromosome called Trisomy resulting in mental and physical disabilities.
People suffering reproductive difficulty can determine whether they have a chromosome abnormality by having a blood test for chromosome analysis called a karyotype. Even if the blood test does not indicate an abnormality chromosome abnormalities may still exist in sperm (especially in men with abnormal sperm parameters) and more commonly in eggs (especially in women as they age).
If you are experiencing recurrent miscarriage or want to learn more about PGD, please contact us today!