The diagnosis
This patient has presented with the autonomous nervous system dysfunction symptoms which occurred as intermittent episodes of abdominal pain, alternating episodes of constipation and diarrhea with moderate gastritis for many years. He has also exhibited the cutaneous symptoms of photosensitivity which were persistent as a rash with occasional blistering. The initial differential diagnosis can be that he has either hereditary coproporphyria or porphyria variegata due to the mixed symptoms but with no history of developmental delays, we can fix the diagnosis as the hereditary coproporphyria (Mindner and Schneider, 2006, 335).
The acute abdominal pain could be due to an intermediate product of porphyrin called 5-aminolevulinic acid. Heme deficiency in the nervous system sets off the clinical illness. Endogenous or exogenous factors stimulate an increase in the hepatic heme synthesis by the stimulation of ALA or the rate-limiting enzyme delta-aminolevulinic acid synthase. This increased heme and the block in the biosynthesis pathway together contribute to the enhanced levels of intermediates. This is an autosomal dominant type of disease (Marks, 2007). Family members thereby give a history of similar illness. The patient’s father and a paternal aunt had similar illnesses.
The excess faecal secretion of coprophyrins favours the hereditary coproporphyria diagnosis. The urine porphobilinogen is slightly elevated here. The marked elevation that is usually seen with acute symptoms is not seen here due to the symptoms not being so acute. The urine coprophyrins are not elevated as the patient has not presented in an acute stage. The increase of the ALA level is also in favour of hereditary coproporphyria. Elevations of uroporphyrins I & III, coproporphyrins I&III and pre-coproporphyrin are not detected here, thereby ruling out porphyria due to mercury and arsenic poisoning.
Defective enzymes
Hereditary coproporphyria is characterized by a deficiency of coproporphyrinogen oxidase in the mitochondrion. The urine discolouration is due to oxidized porphyrinogens.
Accumulations of porphyrins occur in the skin causing photosensitivity as the porphyrins are fluoresecent (Mindner and Schneider-Yin, 2006, p. 331). The pathophysiology of porphyrias is involved with the genetic deficiency of one of the last seven enzymes which form the heme biosynthetic pathway (Porphyrias, Merck). The heme precursors accumulate causing toxicity.
The deficiency of the first enzyme in the eight for the pathway causes sideroblastic anaemia. δ-aminolevulinate (ALA) dehydratase or porphilinogen synthase is found in the cytosol and involved in the second step to produce porphilinogen which is a precursor to heme, chlorophyll and Vitamin B12. Lead poisoning disarms this enzyme. Its deficiency is rare. Being autosomal recesive, it produces hepatic porphyria with abdominal pain and neuropathy (Marks, 2007).
Porphobilinogen deaminase (or hydroxymethylbilane synthase) in the third step converts porphilinogen into hydroxymethybilane. The genetic predisposition is autosomal dominant (Marks, 2007). Mutations in the gene, which encodes the enzyme catalyzes the head-to-tail condensation of four porphobilinogen molecules into the linear hydroxymethylbilane, are associated with deficiency and acute intermittent porphyria with symptoms of abdominal pain at times, peripheral neuropathy , psychiatric disorders and tachycardia (Marks, 2007). Variants with aternatively spliced transcript encoding different forms have been found (Deybach, 1995).
Uroporphyrinogen III synthase is involved in the fourth step of the prophyrin metabolism and converts hydroxymethyl bilane into uroporphyrinogen III. The deficiency of this enzyme in the cytosol produces the autosomal recessive congenital erythropoietic porphyria which is characterised by severe photosensitivity with erythema, swelling and blistering , hemolytic anaemia and splenomegaly (Marks, 2007).
Uroporphyrinogen decarboxylase is found in the cytosol. The deficiency is autosomal dominant and produces porphyria cutanea tarda with photosensitivity and vesicles and bullae. The UROD gene encodes the fifth enzyme which catalyses the conversion of uroporphyrinogen to coproporphyrinogen through the removal of four carboxymethyl side chains (Elder, 1978).
Deficiency of coproporphyrinogen oxidase found in the mitochondrion produces the autosomal dominant illness of herditary coproporphyria which exhibits photosensitivity and neurological symptoms and colic (Marks, 2007). The enzyme is involved in the sixth step and catalyses the conversion from coproporphyrinogen III to protoporphyrinogen IX. (Lamoril 1995).
Protoporphyrinogen oxidase is found in the mitochondrion and associated with the autosomal dominant illness of variegate porphyria. Photosensitivity, neurologic symptoms and developmental delay are found (Marks, 2007). This enzyme is acting in the seventh step and catalyses the portoporphyrinogen IX to protophyrin IX.
Ferrochelatase is found in the mitochondrion. Its deficiency produces an autosomal dominant illness characterised by photosensitivity with skin lesions, gallstones and mild liver dysfunction (Marks, 2007). It catalyses the terminal step of the porphyrin metabolism by converting protoporphyrin IX to heme. Two transcript variants have been found (Cox, 1997).
DNA testing
DNA testing is done for determining the type of porphyria. Tests are done after the blood, urine and faeces are examined. If a mutation is found in the DNA sequence of a gene, the diagnosis of that porphyria is confirmed. 97% of known disease causing mutations can be detected by DNA analysis (DNA Diagnosis for porphyrias, American Porphyria Foundation). Whether the patient is symptomatic or not does not matter.
The test only requires a small amount of blood. When a mutation has been confirmed, other members of the family can have the tests. Three acute porphyrias have similar symptoms, biochemical results and responses to treatment. It would be difficult to tell between the acute intermittent porphyria, hereditary coproporphyria and variegate porphyria. The method would be to do a triple test for all three.
DNA testing involves a sophisticated method which is multiprocedural, difficult to perform and expensive for sequencing the DNA. The cost ranges from $750 for the first person in the family to $150 for the members of his family (DNA Diagnosis for porphyrias, American Porphyria Foundation). The triple test costs $1750. Results are available with 2-4 weeks. In the US some insurances are accepted by the labs. The test is done on the prescription of a physician.
Management and Prognosis
The prognosis of this patient is good in that his symptoms come on intermittently as he is exposed to chemical substances in the household that he has become sensitive to. Though he has a genetic cause for the porphyria, triggering factors appear to be household chemicals. His present episode is not life threatening (Mindner and Schneider-Yin, 2006). The severe abdominal pain may be treated with opiate analgesics with chlorpromazine of 75 mg/day as infusion. Electrolyte imbalance must be watched and corrected parenterally. All systemic illnesses must be managed accordingly. Severe hypotension and cardiac arrythmias must be ruled out so close monitoring is essential.
Increased amounts of carbohydrate 200-500 gm / day and heme may be administered. If the patient is unable to swallow food, fluids rich in glucose may be administered. Heme is given in the dosage of 3-5mg/kg in short infusions once a day for 3-5 days along with IV fluids as this patient has developed severe weakness and motor paresis is expected (Mindner and Schneider-Yin, 2006). The risk of phlebitis is reduced by adding the heme to 4% albumin and rinsing the area of the prick with physiological sodium chloride solution.
The management in the latency period would concentrate on prevention of repeated attacks by avoiding precipitating factors. Starvation should be avoided. Photosensitivity must be managed well. General measures like wearing long sleeved clothes, hats, trousers and staying indoors in the afternoons would be fairly effective. No specific treatment for the skin lesions is necessary.
Prognosis
Urinary porphyrin precursors would reduce within 24 hours after the heme. His abdominal pain would disappear within 2-3 days. The general body weakness would subside with fluids and foods especially carbohydrates. The patient may have repeated attacks if exposed to precipitating factors. The purplish colour of the urine would also disappear.
References
Cox TM (1997). “Erythropoietic protoporphyria.”. J. Inherit. Metab. Dis. 20 (2): 258–69.
Deybach JC, Puy H. (1995). “Porphobilinogen deaminase gene structure and molecular defects.”. J. Bioenerg. Biomembr. 27 (2): 197–205
DNA Diagnosis for porphyrias. (2007). American Porphyria Foundation. Web.
Elder GH, Lee GB, Tovey JA (1978). “Decreased activity of hepatic uroporphyrinogen decarboxylase in sporadic porphyria cutanea tarda.”. N. Engl. J. Med. 299 (6): 274–8.
Lamoril J, Martasek P, Deybach JC, et al. (1995). “A molecular defect in coproporphyrinogen oxidase gene causing harderoporphyria, a variant form of hereditary coproporphyria.”. Hum. Mol. Genet. 4 (2): 275–8.
Marks, Dawn B.; Swanson, Todd; Sandra I Kim; Marc Glucksman (2007). Biochemistry and molecular biology. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.
Minder, E. and Schneider-Yin, X. (2006). “Physician’s Guide to the Treatment and Follow-Up of Metabolic Diseases”. Published by Springer-Berlin Heidelberg.
Woods, J.S. (1995), “Porphyrin metabolism as indicator of metal exposure and toxicity”, in Goyer, R.A. & Cherian, M.G., Toxicology of metals, biochemical aspects, 115, Berlin: Springer, pp. 19–52, Chapter 2.