National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Autosomal erythropoietic protoporphyria

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Can a genetic carrier of EPP be symptomatic?

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.

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GARD Information Specialist

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  1. Erythropoietic Protoporphyria (EPP) and X-Linked Protoporphyria (XLP). American Porphyria Foundation. 2015; http://www.porphyriafoundation.com/about-porphyria/types-of-porphyria/EPP-and-XLP.
  2. Deybach JC, Lecha M, Puy H. Autosomal erythropoietic protoporphyria. Orphanet. July 2013; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=en&Expert=79278.
  3. Poh-Fitzpatrick MB. Protoporphyria. Medscape Reference. 2016; http://emedicine.medscape.com/article/1104061-overview.
  4. Balwani M, Bloomer J & Desnick R. Erythropoietic Protoporphyria, Autosomal Recessive. GeneReviews. 2017; http://www.ncbi.nlm.nih.gov/books/NBK100826/.
  5. Balwani M, Bloomer J, Desnick R. X-Linked Protoporphyria. GeneReviews. February 14, 2013; http://www.ncbi.nlm.nih.gov/books/NBK121284/.