It’s slightly different in different centres. We try to minimize the genetic risk in the offspring, this is a global idea, but we have to make specific points about it. How do we work with all these huge amounts of options that we have? We work with carrier maps or maps of genes. There are two types of genetical sicknesses, the dominant ones that mean that we have two copies of the genotype, one coming from our mother, one coming from our father, so these two copies are the same, but complementary. If there’s a sickness or mutation in a gene which is dominant, it means that either maternal copy or paternal copy has the copy that is alternated. It’s the wrong copy, the other copy is not going to be able to compensate for this problem, so the individual will be sick. These sicknesses are not a worry to us because we see it.
If the donor is a carrier of a dominant genetical problem, we see it, it’s going to be in her medical history, so it doesn’t worry us so much because most of them, they show up. The problem is when we have these the recessive sicknesses, which means we have two copies if there’s one copy which is wrong and one copy that it’s right, the right copy compensates the wrong copy, so the sickness doesn’t appear, it’s a healthy person carrying a sickness.
The problem comes if the exact mutation comes from the mother and from the father, so we have wrong and wrong, no rights to compensate, these are the recessive sicknesses. What worries us is what’s going to happen if we have a donor carrying sickness and the partner of the recipient is a carrier of the same sickness, that would be a problem because a quarter of the offspring, 25% would be a sick kid, so this is what we want to avoid.
We are carriers of many little mutations that the other copy compensates, so all of us are carriers of these mutations, the problem with the mutations, that are very low in the population has a very low frequency in the population, it’s not a problem because it’s very rare that the same sickness of these rare sicknesses is going to be the same in the donor and in the partner or in the other donor of sperm. The problem comes from sicknesses that are pretty common in the population, such as cystic fibrosis, the mucoviscidosis which in our area is 4% in the population. It comes out with thalassemia, which in our population could be more or less around from 5 to 25% depending on the areas. These are the problematic sicknesses because we except high enough chance to be worried that maybe the donor and the partner of this recipient could be carriers of these sicknesses that are prevalent in the population.
There are two types of confronting this, either by performing carrier map test in all the donors and all the partners that are in treatments. The carrier map is a list of 300 sicknesses from the most frequent to the lowest frequency that is not in the donor and in the partner of the recipient of the sperm donor, and we match the results, meaning we are not looking for a perfect genotype that doesn’t have the mutation, we are looking for risk of coincidence of the same sickness between the donor and the partner.
This is one approach where we decrease the risk a lot of the sickness because we are matching this risk but we don’t filter for carriers, so maybe the offspring is going to be a carrier of cystic fibrosis that is also common in the population and maybe we’ll have to advise that this child has to go for cystic fibrosis counselling when they want to have children, but usually, this information is not given, so what we decided is to go 50/50. We perform this carrier map excluding the donors for the most common sickness in the population such as cystic fibrosis but also other 16 sicknesses that are located in chromosome X, we do these tests on the donors, and if they are positive, we give them counselling, and we don’t accept these donors in our centre.
We have this common sickness excluded, and then the carrier map is optional for patients, for the recipients. The problem with carrier maps is that they are expensive, so if the recipients want to double-check other sicknesses that are low prevalence in the population, they have the option to do it. If not, we have the basic panel available, so we have the most common sicknesses in the population excluded, so we are good with this 50/50, we don’t create carriers of mucoviscidosis f. e. but we can also increase the number of tests if the patient wants to.