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Genetic Testing Lab

Test Catalog Molecular Genetics Laboratory Porphyria Cutanea Tarda

Porphyria Cutanea Tarda

Test Description:

PCT is a deficiency of the enzyme uroporphyrinogen decarboxylase in the heme biosynthesis pathway. Cutaneous blisters develop on sun-exposed areas of the skin such as the hands and face. The skin in these areas may blister or peel after minor trauma. Increased hair growth as well as darkening and thickening of the skin may also occur. Neurological and abdominal symptoms are not characteristic of PCT. Liver function abnormalities are common, but are usually mild. PCT is often associated with hepatitis C infection, which also can cause these liver complications. However, liver tests are generally abnormal even in PCT patients without hepatitis C infection. Progression to cirrhosis and even liver cancer occurs in some patients.

Porphyria cutanea tarda (PCT) is the most common type of porphyria, with a prevalence of approximately 1 in 10,000. PCT develops when the activity of the enzyme uroporphyrinogen decarboxylase (URO-decarboxylase) becomes severely deficient (less than 20% of normal) in the liver. In most cases these patients do not have URO-decarboxylase gene mutations and are said to have sporadic (or Type I) PCT (s-PCT), About 20 percent of cases have familial (or Type II) PCT (f-PCT). Such individuals have inherited a URO-decarboxylase gene mutation from one parent, which has reduced the amount of URO-decarboxylase in all tissues from birth. However, to develop symptoms, other factors must be present to reduce URO-decarboxylase level in the liver to less than 20% of normal. Such f-PCT patients may develop blisters at an early age or have relatives with the disease. Excess iron and multiple other susceptibility factors contribute to the development of PCT. These include use of alcohol or estrogens, smoking, chronic hepatitis C, HIV (human immunodeficiency virus), and mutations of the HFE gene which is associated with the disease hemochromatosis. Other factors remain to be identified. A URO-decarboxylase inhibitor generated only in the liver accounts for the severely deficient enzyme activity in PCT. 

DNA analysis of the UROS gene is performed by full gene sequencing of all exons (coding regions), 20-30 base pairs into the introns (including splice sites), and the promoter region. This methodology should identify >98% of gene mutations listed in the Human Gene Mutation Database as well as novel mutations.

Prenatal diagnosis is also available. Prior to ordering prenatal testing, please contact our laboratory at 212-241-7518 to discuss. 

Specimen Requirements:

  • Full DNA analysis: 20ml of whole blood in EDTA (anticoagulant) tubes (lavender top) 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.

Turnaround Time
Post-natal: 10-14 days
Pre-natal: 3-5 days

CPT Codes
Full gene sequencing: 81405, 81479, G0452
Targeted mutation analysis: 81403, 81479, G0452

Consent Form: Porphyria Genetic Testing Consent [PDF]

Requisition Form: Porphyria Testing Requisition [PDF]