Preimplantation Genetic Diagnosis (PGD) With PGS for Aneuploidy
PGD is designed for couples who have an increased risk of having a child with a specific genetic disorder or chromosomal abnormality based on their own genetic status. The goal of PGD is to identify which embryos are unaffected with the disorder of concern. PGD is available for:
Single Gene Disorders
Individuals who are identified as carriers of a recessive disorder or who are at risk for/have a dominant genetic disorder are at increased risk of having an affected child. Using DNA samples from you, your partner, and a reference family member, PGD determines which chromosome(s) carry the disease-causing mutation(s). This information provides the disease status for each embryo.
Individuals with a balanced chromosomal translocation typically do not experience any symptoms associated with their chromosomal alteration, however, the gametes (eggs or sperm) have a significantly increased chance of carrying a chromosomal imbalance. PGD determines whether or not a chromosomal imbalance is present in each embryo.
PGS for Aneuploidy Screening
As part of the PGD process (for both single gene disorders and chromosome translocations), embryos are also screened for chromosomal abnormalities. Chromosomes are the structures inside of our cells that contain the genetic information needed for our bodies to grow, develop, and maintain our health. Changes to the number or structure of the chromosomes may cause failure of an embryo to implant, result in a miscarriage, or lead to the birth of a baby with developmental, intellectual and/or physical abnormalities. The goal of PGS for aneuploidy is to identify embryos that are chromosomally normal, and thus have the best chance of successfully implanting and maintaining a pregnancy.
How Is PGD With PGS for Aneuploidy?
CombiMatrix utilizes a technique called Karyomapping, which investigates hundreds of thousands of points along all 23 pairs of chromosomes. For single gene disorders, Karyomapping utilizes information from the parents and a reference family member to identify the exact chromosomal background of the mutation(s), and uses this information to determine whether or not an embryo has inherited the mutation(s). For chromosomal translocations, Karyomapping is able to identify how many copies of the chromosomes involved in the translocation are present, which determines whether or not the embryo has a chromosomally unbalanced form of the balanced parental translocation.
For aneuploidy screening, Karyomapping is used to determine whether there are any extra or missing chromosomes (aneuploidies). For the first 22 pairs (the autosomes), there should be two copies of each chromosome. For the 23rd pair, there should be either two X chromosomes (female) or an X and a Y (male). If there is a gain or loss of the entire chromosome, it is called a whole chromosome aneuploidy. If there is a gain or loss that involves a region greater than 30 Mb in size, it is called a segmental aneuploidy. Most implantation failures and miscarriages are caused by whole chromosome aneuploidy, however, segmental aneuploidies may have a similar effect. Because of the small sample size (one or several cells), it is not possible to identify segmental aneuploidy of regions smaller than 30 Mb in size.
Chromosomal abnormalities are one of the most common reasons for implantation failure and miscarriages that occur within the first 12 weeks of pregnancy. In fact, approximately 50-60% of miscarriages that occur in the first trimester are due to a fetal chromosomal abnormality. Chromosomally abnormal embryos may not differ in overall microscopic appearance from chromosomally normal embryos, making it difficult to identify which embryo(s) have the best chance of resulting in a healthy baby. By implanting a chromosomally normal embryo, the possibility of a successful implantation and pregnancy is significantly enhanced.
What Are The Benefits of PGD With PGS for Aneuploidy?
PGD allows you to select an embryo that is unaffected with the single gene disorder or chromosomal abnormality of concern. While PGS for Aneuploidy is helpful for all couples undergoing PGD, it may be particularly beneficial for couples who:
- Have experienced one or more failed IVF cycles
- Have a history of recurrent miscarriage
- Prefer to have a single embryo transferred
- Have had a previous pregnancy or child with a chromosomal abnormality
- Are at increased risk for aneuploidy due to advanced maternal age
Preimplantation Genetic Diagnosis Literature:
Genetic Counseling Services
Genetic counseling is an integral part of the PGD process. Our board-certified genetic counselors will work closely with you to prepare and guide you through the process.
Michelle Strecker, MS, LCGC
Sara Commander Hay, MS, LCGC
Mary Travis, MS, LCGC
Timeline for PGD With Aneuploidy Testing
Every patient’s situation is unique, which is why we have genetic counselors that specialize in PGD to assist you throughout the testing process. Some laboratories use test techniques that require 3-4 months of test development and validation before PGD can be performed. Karyomapping’s advanced technology allows CombiMatrix to dramatically reduce the time required for test preparation and validation. Below is an outline of the PGD referral and testing process:
- Initial Referral Your doctor will complete and submit a PGD Patient Referral Form, including all relevant genetic testing results (i.e. mutation analysis for single gene disorders or karyotype reports for chromosome translocations). Please note that for single gene disorders, if a specific mutation has not yet been identified in your family, PGD cannot be performed.
- Initial Genetic Counseling Within 72 hours of receiving the referral, a CombiMatrix genetic counselor will contact you to schedule an initial telephone consultation. The purpose of this initial consultation is to review the test results, obtain a detailed family and medical history, and for single gene disorders, identify any suitable family members who could serve as a test reference. Although appointments are typically available for the same or the following day, you are welcome to schedule this consultation at a time and date most convenient to you and your partner.
- Medical Team Review The CombiMatrix Medical Team will review your case and ensure that there are sufficient genetic markers within and surrounding the gene (single gene disorders) or chromosomal region (chromosomal translocations) of concern. The vast majority of cases will be suitable for PGD by Karyomapping, however, it is possible that Karyomapping may not be the best method for PGD, due to decreased coverage of the region of concern or, for single gene disorders, a lack of a suitable reference. If this is determined to be the case, you and your doctor will be notified immediately.
- Second Genetic Counseling Consultation Once your case has been approved, you will be asked to schedule a second genetic counseling telephone consultation to review the design of the testing for your specific situation, discuss the requested reference family member (for single gene disorders only), and review the risks and benefits of PGD With PGS for Aneuploidy. Following this consultation, you and your partner will sign a consent form, pay a deposit of $500 (which is applied to the cost of the testing) and receive DNA collection kits. You and your doctor will receive a personalized consultation note from the genetic counselor following the consultation.
- PGD Test Set Up For single gene disorder cases, the patient, partner and reference family member’s DNA will be run together to optimize the testing. If the reference sample provided is not suitable, a sample from another family member(s) may be requested. If there are any concerns regarding the unique PGD test setup for your family, our medical team will inform both you and your doctor. Since chromosome translocation cases do not require a reference family member, there is no additional test set-up step required for these cases. Patients typically begin their cycle at this point.
- Embryo Testing and Post-Test Genetic Counseling Once we receive the embryo biopsies in our laboratory, testing will be initiated, with results typically available in 12-14 calendar days. After discussing the results with your doctor, a CombiMatrix genetic counselor will follow-up with you to answer any additional questions.