X Linked Protoporphyria
EPP and XLP are both protoporphyrias with similar symptoms and similar biochemical findings, but each is caused by mutations in a different gene. XLP is sometimes called a “variant form of EPP”. XLP an X-linked disorder caused by a mutation in exon 11 of the ALAS2 gene resulting in an increased production of the enzyme, aminolevulinic acid-synthase 2 in the heme biosynthesis pathway. Biochemical testing, specifically total and fractioned erythrocyte protoporphyrin assay, can be done between XLP and EPP.
Symptoms usually first occur in early childhood and include sun sensitivity marked by severe pain and swelling of sun-exposed areas, but typically with no blistering or scarring. Males and females are both affected, although females are typically less severe. Both XLP and EPP result in significant elevations of protoporphyrins in the liver, sometimes resulting in severe liver complications that are difficult to treat and sometimes require liver transplantation.
Molecular analysis for XLP is performed in this laboratory as part of the "Erythropoietic Protoporhyria Panel" (analysis of ALAS2 exon 11 for XLP and the FECH gene for EPP). DNA analysis of exon 11 of the ALAS2 gene is performed by full gene sequencing of the exon (coding region) and 20-30 base pairs into the intron (including the splice site). The detection rate has not been determined.
Targeted mutation analysis, looing for the specific family's ALAS2 exon 11 mutation, can also be performed. Documentation of the family's mutation must be provided.
Prenatal diagnosis is also available. Prior to ordering prenatal testing, please contact our laboratory at 212-241-7518 to discuss.
- Full DNA analysis ("Erythropoietic Protoporphyria Panel" only): 20ml of whole blood in EDTA (anticoagulant) tubes (lavender tops) OR extracted DNA (50μl with concentration of 200ng/μl).
- Targeted Mutation Analysis: 20ml of whole blood in EDTA (anticoagulant) tubes (lavender top) OR extracted DNA (30μl with concentration of 200ng/μl) OR buccal cells (buccal brushes MUST be requested from laboratory).
Prenatal: Testing requires prior documentation of parental mutation.
- Chorionic Villi: 5-10 mg in conical tube with sterile saline OR transport media
- Amniotic Fluid: 10 ml in conical tube
- Cultured Cells: two confluent T-25 flasks
Additionally, please send:
- 5-10 ml maternal blood in EDTA (lavender top) required to perform MCC studies on all prenatal samples and in case maternal confirmation studies are necessary
- 5-10 ml paternal blood in EDTA (lavender top) in case paternal confirmation studies are necessary
Shipping: Ship at room temperature.
Post-natal: 10-14 days
Prenatal: 3-5 days
Full gene sequencing: 81406, 81479, G0452
Targeted mutation analysis: 81403, 81479, G0452
Consent Form: Porphyria Genetic Testing Consent [PDF]
Requisition Form: Porphyria Testing Requisition [PDF]