If you have porphyria, the thought of potentially passing the disease on to your children can be stressful. There are options to limit the risks, however, and help is available for family planning.
How do children inherit porphyria?
Mutations in different genes may cause porphyria. Depending on the gene, some forms of porphyria are inherited in an autosomal dominant pattern, some an autosomal recessive pattern, and some an X-linked recessive pattern.
Humans have 23 pairs of chromosomes. Of these, 22 are called autosomal chromosomes, or numbered chromosomes. One pair, fittingly called the sex chromosomes, determine the sex of the child. Chromosomes carry the genes that contain the instructions necessary to make different proteins. People generally inherit a copy of each chromosome from each biological parent.
Autosomal dominant inheritance
In autosomal dominant inheritance, if a child acquires a chromosome carrying a faulty gene from one parent, he or she will develop the disease that the faulty gene causes. So if you or your partner have a type of autosomal dominant porphyria that has an autosomal dominant inheritance pattern, your children will have a 50% chance of inheriting it.
Autosomal recessive inheritance
If the disease has an autosomal recessive pattern of inheritance, your child would need to receive two defective copies of the gene — one from each of you — to develop porphyria. Since it requires both parents to have mutations in the gene and for the child to inherit the mutated copy from each parent, these forms of porphyria can be very rare. If the child only receives one copy of the faulty gene, he or she will be a carrier of the disease like the biological parents.
X-linked recessive inheritance
In the X-linked recessive pattern of inheritance, the faulty gene is on the X chromosome. Girls have two X chromosomes, one that they inherit from each parent. Boys only have one X chromosome that they inherit from their mother and a Y chromosome that they inherit from their father. X-linked recessive diseases are, therefore, much more common in males than in females. This is because the second X chromosome in females can generally compensate for the faulty copy of the gene.
So if a father has a form of X-linked recessive porphyria, he will not pass the disease onto any of his sons. However, he will pass it onto all his daughters. If the mother is a carrier for the disease, her sons will have a 50% chance of inheriting the disease. Her daughters will have a 50% chance of being carriers.
Can porphyria affect pregnancy?
If you are a woman with porphyria, you can still become pregnant. However, pregnancy may aggravate your disease and its symptoms. During pregnancy, the levels of a hormone called progesterone increase in your body. This can lead to acute porphyria attacks.
Mothers with porphyria also may be at risk of having a complicated pregnancy and birth. A large study reviewed information about mothers with and without porphyria in Norway. It found that mothers with porphyria could be at a higher risk of having children with low birth weight, and losing their babies before or shortly after birth. Mothers with porphyria also could have an increased risk of developing preeclampsia during pregnancy and giving birth through cesarean section (C-section).
If you have porphyria and are planning to become pregnant, you should discuss your options with your physicians and a genetic counselor.
Prenatal genetic diagnosis
If you do become pregnant, there is the option to test your child for porphyria before the baby is born. This is called prenatal genetic diagnosis. Doctors collect samples of DNA from the fetus in order to screen them for the genetic mutations that could lead to porphyria. This can be done using two different methods: chorionic villus sampling, or CVS, and amniocentesis.
CVS is performed by the doctor usually between 10 and 12 weeks of gestation. During the procedure, the physician will insert a catheter through the vagina or a long needle through the abdomen to collect small finger-like projections, called villi, from the placenta. The placenta serves as a “lifeline” to the baby during pregnancy, delivering blood and nutrients. Clinicians can then use the cells from the villi for genetic screening for porphyrias.
Amniocentesis generally is done somewhat later in the pregnancy, usually between 15 and 20 weeks of development. Here, doctors will insert a long needle through the abdomen and into the amniotic sac in order to sample the amniotic fluid that surrounds the baby. The amniotic fluid contains cells from the fetus, which clinicians can use for genetic testing.
In vitro fertilization and preimplantation genetic diagnosis
The process of IVF involves taking sperm from the father and eggs from the mother and combining them in a laboratory to create embryos. Doctors can then implant one or more embryos into the mother’s uterus to result in pregnancy.
PGD involves taking small samples from each of the embryos before implantation and performing screening for genetic mutations. Based on the results of the genetic screening, parents can decide whether they want to proceed with the pregnancy.
Other reproductive options using IVF
There are a few other options available as well. You could use sperm or eggs from a donor who isn’t affected by porphyria for IVF. In this instance, the resulting child would not be genetically related to the partner with porphyria.
If the risks of pregnancy with porphyria are too high, you and your partner could look into IVF with a surrogate for the pregnancy.
Last updated: Oct. 20, 2020
Porphyria News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
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