Diagnosis
When diagnosing Congenital Erythroipoetic Porphyria (Gunther Disease) one must exclude other forms of porphyria. These include Hepatoerythropoietic Porphyria and rare homozygous variants of Variegate Porphyria, Hereditary Coproporphyria, and STING-associated vasculopathy with onset in Infancy (SAVI). Mild variants may be present similarly to Porphyria Cutanea Tarda.There are four steps in establishing the diagnosis of any porphyria. First, a thorough history (particularly family history) and physical exam are performed with special attention paid to sun-exposed skin. Biochemical measurements of porphyrins and precursors in the urine, feces, and blood are necessary. Specialized labs are helpful in measuring activity of specific enzymes of the heme synthesis pathway and/or DNA and mutational analyses. In CEP, activity of uroporphyrinogen III synthase (the fourth enzyme in the heme biosynthetic pathway) will be markedly decreased.In congenital erythropoietic porphyria, urine aminolavulanic acid and porphobilinogen are typically normal. However, uroporphyrin and coproporphyrin tend to be markedly elevated and moderately elevated, respectively, in the urine more than in the feces. Additionally, fecal protoporphyrin is typically mildly elevated.In the red blood cells, uroporphyrin, coproporphyrin and protoporphyrin are all elevated, distinguishing this form of porphyria from the others. Finally, plasma analysis will demonstrate elevated uroporphyrin and coproporphyrin.Other nonspecific but helpful diagnostic clues are history of cutaneous photosensitivity, blistering, erosions, crusts and ulcerations leading to extensive scarring and deformation of the hands, loss of eyebrows, eyelashes with severe mutilation of cartilaginous structures like the nose, erythrodontia, and variable degree of hematologic involvement ranging from mild hemolytic anemia to intrauterine hydrops fetalis.
Porphyrins additionally accumulate in the bone and teeth, resulting in erythrodontia. When unexpected attacks occur, abdominal pain, as well as vomiting and constipation commonly follow the attacks. Exposure to the sunlight can cause discomfort and result in blistering, consciousness of heat, and swelling and redness of the skin. Complications
Photomutilation and transfusion-dependent anemia are common complications. Liver disease is also observed in some cases. It has been reported that early childhood-onset haematological manifestations is a poor prognosis factor. Causes
Gunther disease is caused by mutations in the gene that encodes the enzyme uroporphyrinogen III synthase (UROS), located at human chromosome 10q25.2-q26.3. The disorder is inherited in an autosomal recessive manner. This means the defective gene is responsible for the disorder and is located on an autosome, and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder. When there is a homozygous mutation it causes a uroporphyrinogen III synthase and uroporphyrinogen cosynthase defect. When the enzyme uroporphyrinogen III synthase is reacting normally it results in the making of isomer III porphyrinogen, which is what is used to form heme. When isomer III porphyrinogen is not produced because of a poor production of uroporphyrinogen III synthase then isomer I porphyrinogen is made which will oxidize and give a reddish tint skin.