Some severe genetic disorders are sex-linked, that is they are due to disorders of either the X or the Y chromosomes. Sex selection, often wrongly termed gender selection, is not only ethical and legal but could also, in many cases, help to avoid having children born with severe genetic disorders. For parents who are carriers of certain X or Y linked disorders and don’t want to pass on that genetic disorder to their children, sex selection may be offered as the most optimal treatment. In this article, we will help you understand how sex selection can help you prevent these genetic disorders running in your family and have a healthy baby.
What is a Genetic Disorder?
Your DNA, found on almost every cell in your body, is the blueprint for the entire functioning of your body. The DNA is broken up into chromosomes, 46 in total, 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes. At intervals along each chromosome are genes, each gene a fundamental functional unit of heredity. These genes code for making different proteins essential to the normal function of your body. They range from making proteins essential to the structure of your body, proteins that generate hormone and enzyme production (eg. Insulin), and genes which decide your characteristics (eye colour, hair colour etc.). Sometimes however, there is a mutation or change in a gene, or multiple genes, which causes the gen to code improperly, and leads to a “genetic disorder”.
The mutation can occur spontaneously before a fertilized egg develops into an embryo, during embryo development, in adulthood, or it can be inherited from parents who are a carrier of a faulty gene and who may or may not have such a disorder themselves.
How Is a Baby’s Sex Connected to a Genetic Disorder?
Usually a female has two X chromosomes, and a male one X and one Y chromosome. A baby inherits one X chromosome from its mother, and either an X or a Y chromosome from the father. If the father contributes a Y chromosome the sex of the baby is male, and if the father contributes an X chromosome, the sex of the baby will be female.
Where the parent’s mutated gene is located on the sex chromosomes, then that has particular effects dependent upon the sex of the baby, as compared to where the mutated gene is on an autosomal chromosome. When the problem is X-linked in the mother, that is the mutated gene is on one of the mothers, the severity of the inheritance is higher in males who have only one X chromosome (they are “XY”), and the X-linked disorder is fully expressed. In contrast, symptoms in females are less severe or even none, because even if one X chromosome has the mutated gene, there is another X (from the pair of sex chromosomes “XX”) which is normal. This means PGT-M can be offered to select unaffected or carrier embryos.
Where the mutated gene is on the father’s X chromosome (assuming it is an X-linked disorder not severe enough to stop him having children), all female children will be carriers, and all male children will be unaffected (males only inherit the father’s Y chromosome). Similarly, where the mutated gene is on the father’s Y chromosome (assuming it is an Y-linked disorder not severe enough to stop him having children), then all males will inherit the disorder, and all females will be unaffected. In all cases where the mutated gene is on the father’s chromosomes then can only offer PGT-A to select the sex of the embryo in order to avoid passing on the disorder.
Examples of common X-linked disorders include red-green color blindness, hemophilia, Duchenne muscular dystrophy, X-linked agammaglobulinemia, Alport syndrome, Charcot-Marie-Tooth, Fabry disease, etc.
Examples of common Y-linked disorders include Y Chromosome Infertility, Swyer syndrome, Hypertrichosis of the ears, Webbed Toes Syndrome, Porcupine Man, etc.
While for most X-linked diseases males are more affected than females, with Y-linked disorders only males will be affected since females do not have a Y chromosome.
Thanks to the advanced assisted reproductive technologies available today, a couple doesn’t have to wait until the female is pregnant to test for any genetic disorder, and either potentially terminate or have a child with a genetic disorder. We can use Pre-implantation Genetic Testing (PGT), an accurate and reliable technology, to test embryos and detect genetic disorders and/or chromosomal disorders. This testing also reveals the sex of the embryo. We can then select embryos with a healthy chromosome profile for transfer, preventing passing on genetic diseases, and providing higher rates of pregnancy, healthier pregnancies, and healthy babies. The PGT technique requires an IVF/ICSI ovarian stimulation cycle, and the expertise of embryologists and genetic scientists to provide these services. You can read in more detail about the types of PGT here.
Who Should Be Concerned about Sex-linked Genetic Disorders?
As mentioned above, couples who are aware that, or think that, one or both of them might be carriers of X-linked disorders and/or Y-linked disorders, and are greatly concerned that they might pass such diseases onto their children.
Besides sex-linked diseases, sex selection may also be permitted and used in other common diseases, which have no specific gene known but have significantly higher rates in one sex, such as certain types of diabetes, blindness, sclerosis, dementia, autism etc. The age of the mother is one of the factors where there is an increased risk of many genetic disorders, and therefore may warrant having sex selection. Professor Rasmus Nielsen from the Natural History Museum of Denmark, the University of Copenhagen and the University of California, Berkeley, revealed that, “The older a woman is, the greater number mutations have occurred in her ova, thus increasing the risk of her children being born with various genetic diseases.”
In summary, parents who concerned about passing on a known familial genetic/hereditary disease to their children, are recommended to consult a qualified doctor to see what options are available to help in preventing or minimizing such risks. For some medical conditions, sex selection (sometimes wrongly called gender selection) in conjunction with IVF/ICSI treatment, may be advised. Consulting with the doctor will help you decide which option is most suitable for you.
Where to Start If I Am Concerned?
You can start by scheduling an appointment to visit an experienced fertility clinic and discuss your concerns with the doctor. After assessing all of the details, the doctor can outline and discuss your available options.
Conclusion The sex selection process is permitted and used for medical reasons to prevent sex-linked disorders where a child’s sex is considered to be a direct factor in whether he or she is likely to develop a disease. Medical sex selection can also be more generally used to help prevent parents from passing on other common genetic disorders to their children if it is considered by a doctor to be for medical purposes.
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