Will My Child Inherit My Porphyria?
If you have a rare genetic disease like porphyria, you may be wondering whether your children could inherit the disease. Differing types of porphyria can have different inheritance patterns, and their disease-causing mutations can be found in differing genes.
If you are planning to expand your family, you may want to discuss with your doctor and a genetic counselor whether you — and possibly your partner — should have a genetic test.
What causes porphyria?
Autosomal recessive inheritance
Autosomal recessive inheritance means that children have to inherit two copies of a disease-causing mutation (one from each parent) to develop the disease. If you have two copies of a disease-causing mutation (meaning that you have a recessively-inherited type of porphyria), but your partner has no copies of a disease-causing mutation, your children are very unlikely to inherit your disease. They will all have one copy of a disease-causing mutation, and one healthy copy of the gene from your partner, and be a carrier of the disease.
If your partner is a carrier, however, your children have a 1 in 2 chance of developing the disease. They will also have and a 1 in 2 chance of being a carrier.
Autosomal dominant inheritance
In autosomal dominant inheritance, a single copy of a disease-causing mutation is sufficient to cause the disease. If you have one copy of a disease-causing mutation but your partner does not, your children will have a 1 in 2 chance of inheriting your disease.
X-linked recessive inheritance
Most people have two sex-determining chromosomes. Females have two X chromosomes, while males have one X chromosome and one Y chromosome. Males inherit their Y chromosome from their father and their X chromosome from their mother. Females inherit one X chromosome from each parent.
If the father has X-linked porphyria, he can only transmit the disease to his daughters. As long as the mother has no copies of a disease-causing mutation, none of their children should have the disease. (For most women, a single copy of the disease-causing mutation is not sufficient to cause this disease.)
However, if a male child inherits a disease-causing mutation from his mother, he will develop this type of porphyria because males have no second X-chromosome to compensate. If the father has this type of porphyria, the mother should be tested genetically to determine whether she is a carrier. This is because in this case, the risk of their children inheriting the disease greatly increases.
How are different types inherited?
Mutations in ALAD and UROS cause porphyria with autosomal recessive inheritance, while mutations in HMBS and CPOX are cause porphyria with autosomal dominant. Mutations in UROD can cause porphyria with either autosomal dominant or recessive inheritance.
ALAS2 and FECH are on the X chromosome, and disease-causing mutations in these genes cause porphyria with X-linked recessive inheritance.
It is important to note that even if a child inherits a disease-causing mutation, it may not be possible to determine how severe their disease will be.
Last updated: Aug. 4, 2020
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