The following information may help to address your question:
What causes erythropoietic protoporphyria (EPP)?
In most cases, EPP is caused by
mutations in the ferrochelatase (
FECH)
gene. Another type of protoporphyria caused by mutations in the delta-aminolevulinic acid synthase-2 (
ALAS2) gene is known as
X-linked protoporphyria (XLP). XLP have almost the same symptoms as the EPP in males, but appears to have a higher risk for liver problems than does EPP.
[1][2][3]
Last updated: 4/11/2018
How can I find out if I have erythropoietic (EPP) or X-linked protoporphyria (XLP)?
DNA studies are important for confirming the diagnosis of EPP and XLP and for the purposes of
genetic counseling. Testing should first be done in a person known to have the disease so that the information about the mutation in that individual can be used to guide testing of other family members.
[1]
Last updated: 3/22/2016
How is erythropoietic protoporphyria (EPP) inherited?
EPP is
inherited in an
autosomal recessive manner. In most cases, affected individuals have one severe (loss-of-function) mutation that is inherited from one parent, and another weak (low-expression) mutation that is inherited from the other parent. In a small number of cases, an affected individual has two loss-of-function mutations.
[1][4] When 2
carriers of an autosomal recessive condition have children, each child has a:
- 25% (1 in 4) chance to be affected
- 50% (1 in 2) chance to be an unaffected carrier like each parent
- 25% (1 in 4) chance to be unaffected and not be a carrier
Last updated: 4/11/2018
How is X-linked protoporphyria (XLP) inherited?
XLP is inherited in an
X-linked manner.
[1][5] Women with an
ALAS2 mutation have a 50% chance of passing on the disease-causing mutation to each child. Males who are affected transmit the disease-causing mutation to all of their daughters and none of their sons.
[5]
Last updated: 3/22/2016
Can a genetic carrier of erythropoietic protoporphyria (EPP) exhibit symptoms?
In EPP caused by
FECH mutations, carriers (
heterozygotes) and individuals who inherit two low-expression mutations typically do not exhibit symptoms.
[1][4]
Female carriers (heterozygotes) for XLP may develop clinical findings related to the disorder. Symptoms may range from those typically observed in affected males, to being completely symptom-free.
[5]
Last updated: 3/22/2016
We hope this information is helpful. We strongly recommend you discuss this information with your doctor. If you still have questions, please
contact us.
Warm regards,
GARD Information Specialist
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