15th March 2013 | by Dr. William Buckett
My husband and I want to have a baby, but we’re scared of passing on a disease/genetic mutation. What are our options?
Principally, that depends on what particular genetic disease or mutation you have or are at risk of having. A genetic disorder is a disease that is caused by an abnormality in an individual’s DNA. Abnormalities can range from a small mutation or error in a single gene to the addition or subtraction of an entire chromosome or set of chromosomes.
Many diseases have a genetic predisposition and involve multiple mutations in many genes as well as environmental influences. Examples of these types of disease are late-onset (type 2) diabetes, thyroid disease, and some types of ovarian or colon cancer. At present, screening for many of these multifactorial diseases is not possible and lifestyle changes, avoidance of risk factors, and regular monitoring are the mainstay of care.
Other genetic diseases, such as Down’s syndrome (with an extra chromosome 21), or Cri-du-chat syndrome (with part of chromosome 5 missing), usually occur sporadically but in rare cases may result from abnormalities in the chromosomes of either parent. These diseases can be screened for during pregnancy, with chorionic villus sampling (CVS) or amniocentesis. Screening of embryos before implantation during an IVF cycle (PGD) can also be done.
Single gene disorders, such as cystic fibrosis (a mutation or deletion of a single gene on chromosome 7) or sickle-cell anaemia (a mutation on a single gene on chromosome 11), do occur in families if both parents are carriers, with any pregnancy having a 25% chance of being affected. Where there is a high risk, parents can be tested to see if they are carriers of the defective gene and then either prenatal testing on any pregnancy or pre-implantation testing on any embryo during IVF can be done.
Individuals or couples with a known or suspected increased genetic risk should undergo pre-conception genetic counselling. This is done by referral to the local hospital or community based genetics department. On the basis of their particular genetic risk-profile and in the light of their personal and moral weighing of relevant considerations, the couple may then decide to:
1) get pregnant and have a child while accepting the genetic risk
2) get pregnant and then use prenatal diagnosis (CVS, amniocentesis, ultrasound, or cordocentesis) to determine whether the pregnancy is affected and then consider having an abortion if the pregnancy is affected
3) get pregnant through in vitro fertilization (IVF) using pre-implantation genetic diagnosis (PGD) on the embryos before transferring them with the hope of being able to select a non-affected embryo
4) refrain from having children genetically related to the partner that carries the genetic mutation, and instead consider using donor sperm, donor eggs or donated embryos
5) consider adoption
Obviously, any decisions are strongly based on the genetic risks; the nature of the genetic disease; the risks, costs, and availability of treatments such as IVF and PGD; and their own personal reproductive history. Therefore, in your particular case it is difficult to give options/advice as your own risks and benefits would be different if you were both carriers of sickle-cell disease, for example, compared to if you had previously had a child with Down’s syndrome.
Pre-conception carrier screening (testing) has been used for individual single-gene genetic diseases in populations with increased risk of that particular disease (1) – examples include carrier screening for cystic fibrosis amongst white European populations, for β thalassemia amongst Mediterranean populations, for sickle-cell disease amongst West African populations, and for Tay-Sachs disease and cystic fibrosis amongst Ashkenazi-Jewish populations.
Therefore, presuming you are both healthy and there is no family history of genetic disease, it would be reasonable to consider requesting carrier testing only if your physician feels your ethnic origins warrant it, and if any results are positive to then be referred for individual pre-conception genetic counselling. However, if there is a personal or family history of genetic disease, then referral for pre-conception genetic counselling is recommended. At that appointment, depending on the genetic disease(s) and your individual risks, further investigations may be appropriate and a fuller discussion of your reproductive options, as outlined above, would take place.
- De Wert GMWR, Dondorp WJ, Knoppers BM. Preconception care and genetic risk: ethical issues. J Community Genet. 2012; 3(3): 221–228.