| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Technical Briefs |
1
Porphyria Reference Laboratory, Rabin Medical Center, Beilinson Campus, Petah Tiqva, Israel 49100
2
Emergency Department, Sapir Medical Center, Kfar Saba, Israel 44281
3
Department of Pediatrics A, Schneider Children’s Medical Center, Petah Tiqva, Israel 49202
4
Drug Information Center, Rabin Medical Center, Beilinson Campus, Israel 49100
5
Department of Medicine D, Soroka University Hospital and Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel 84101
6
Department of Clinical Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel 69978
aauthor for correspondence: fax 972-3-937 7710, e-mail nschoenfeld{at}clalit.org.il
Hereditary neuroporphyrias [aminolevulinate dehydratase deficiency porphyria, acute intermittent porphyria, hereditary coproporphyria, or variegate porphyria (VP)], and lead poisoning (LP), which is thought to be an acquired form of neuroporphyria, are characterized by enzymatic inhibitions along the heme biosynthetic pathway (1)(2)(3). As a result, they share a few biochemical and clinical features. For this reason, LP may erroneously be diagnosed as hereditary porphyria, especially in cases when LP arises from unexpected sources such as consumption of Chinese herbal tea (4) and others (5)(6). Because LP is not suspected, direct determination of blood lead is not analyzed and LP is misdiagnosed. This work addresses the problem from a biochemical rather than a clinical standpoint, aiming at defining biochemical criteria that can differentiate LP from acute neuroporphyria and enable the staff in porphyria reference laboratories to diagnose LP indirectly.
The study was based mainly on the biochemical findings in patient 1, whose clinical case has been reported previously in detail (7). The patient, a 43-year-old man, was referred to the hospital because of severe abdominal pain followed by constipation. He was given diclofenac, and further deterioration was noted. Because of the data described above and the fact that his urine had a color of "port wine", an acute attack of neuroporphyria was suspected. The procedure that led to the exclusion of hereditary neuroporphyria and the establishment of a diagnosis of LP are described below. The diagnosis was confirmed by the toxicology laboratory in which a blood lead concentration of 5.3 µmol/L was measured (upper limit of normal, <0.97). The source of LP was an Indian herbal remedy the patient had taken to treat mild diabetes for 3 months before hospitalization. Each pill (8 per day) contained 10 mg of lead, leading to a monthly intake of 2.4 g.
The diagnosis of an acute attack of hereditary porphyria could have been erroneously established in the patient (patient 1) when only the results of the preliminary determinations had been taken into account. Those data revealed 4- and 65-fold increases of porphobilinogen (PBG) [determined by the reliable method of Buttery and Stuart (8)] and porphyrins (9) in 24-h urinary collections, respectively (Table 1
). Moreover, additional biochemical tests carried out in the stool (9) and blood (10)(11) could have even led to narrowing the diagnosis to variegate porphyria (12)(13)(14). Those findings were as follows: (a) increased fecal coproporphyrin (COP) and protoporphyrin [(PP); 2- and 3-fold, respectively] and reversal of the ratio of fecal COP isomers (III > I); (b) increased (3.3-fold) erythrocyte PP; and (c) a peak at 
630 nm in the fluorescence spectrum of the plasma sample (Table 1
).
|
However, to complete the work up, urinary aminolevulinic acid (ALA) (15) was determined, revealing a 40-fold increase. The fact that the ALA/PBG ratio was highly increased (10-fold that of normal), concomitantly with the finding that the inhibited activity (87%) of ALA dehydratase (ALAD) in erythrocytes (16)(17) was induced 10-fold in the presence of zinc and cysteine (Table 1
), led to the suspicion of LP rather than hereditary ALAD deficiency.
To verify whether the urine, feces, and blood findings in patient 1 were specific to his case, we retrospectively studied four other cases of acute LP, referred to the Porphyria Reference Laboratory during the last 3 years, suspected of having an acute attack of hereditary neuroporphyria.
Patient 2, a 38-year-old woman, came to our center after hearing about the case of patient 1. She had been taking the same pills at a lower dosage and had stopped them 3 months before. She was still complaining of muscle weakness, and her blood lead was 2.3 µmol/L. Patients 3 and 4 were Bedouin sisters (19 and 22 years of age, respectively) who consumed bread made of lead-contaminated, home-made flour. The lead was used for stabilizing the metal parts of stone mills (18). Their blood lead concentrations were 2.3 and 3.0 µmol/L, respectively.
Patient 5, a male, age unknown, was exposed to lead at his workplace.
On the basis of the clinical symptoms, patients 1, 3, 4, and 5 were in the acute phase, whereas patient 1 after treatment (designated 1* in Table 1
) and patient 2 were in the nonacute phase.
The findings observed in patients 2–5, i.e., increased urinary porphyrins and precursors (Table 1
), and abnormal porphyrin profile in feces and erythrocytes (not shown) resembled those found in patient 1. Most of them demonstrated close resemblance to hereditary neuroporphyria in general and VP in particular.
Two findings seem to be characteristic to LP: highly increased urinary ALA/PBG ratio and abnormal fluorescence scan of plasma. A marked difference between the nonacute and acute cases could be made on the basis of the ALA/PBG ratio, being 4.4 and 5.8 in the former and ranging between 13–40 in the latter.
The inhibition in erythrocyte ALAD activity, a characteristic phenomenon in LP (19) observed in all the patients studied (Table 1
) was not correlated with either urinary ALA (r = 0.014, P, not significant) or urinary PBG (r = 0.15; P, not significant), whereas it was significantly correlated with the ratio of PBG/ALA (r = 0.964; P <0.001).
The fluorescence spectra of the plasma were abnormal in all five LP patients in both nonacute and acute states, being more pronounced in the latter. Characteristic emission spectra (excitation at 404 nm) of patients in both states, revealing an emission peak at 635 nm, rather than at 629 as in VP, are shown in Fig. 1
. Moreover, the peak was extremely unstable and practically disappeared within 2 h after dilution in saline, whereas the emission spectrum of VP remained relatively stable during the same period. The stability of the latter may be explained on the basis of data published previously (14), relating the profile of the plasma porphyrins in VP to the presence of a complex of peculiar protein bound tightly to porphyrins and characterized by an emission peak at 629 nm (14).
|
It is well established that both zinc-PP (ZnPP) and PP accumulate in the blood of LP patients with a preponderance of ZnPP (20)(21). However, because ZnPP is bound to hemoglobin at the heme binding sites whereas PP is bound to hemoglobin as free base at sites other than heme binding sites, the rate of diffusion to plasma is greater for PP than for ZnPP. On the basis of the findings described above, it may be assumed that the emission maximum at 635 nm observed in the plasma of the five LP patients (much more pronounced in the acute state) is the result of the presence of PP, the porphyrin characterized by an emission spectrum with a peak at 635 nm. This conclusion may be supported by the finding that the spectrum of the plasma of the LP patients resembled both in its shape and instability the spectrum of the plasma of an erythropoietic protoporphyria patient, in which the abnormality in the spectrum is apparently because of the presence of a high concentration of free PP (20).
To differentiate between the genetic (22)(23) and the acquired situation, ALAD activity is determined in the absence and presence of cysteine and zinc. We suggest replacing the determination of the enzyme activity by the plasma emission scanning method, a much quicker, less expensive, and less time-consuming method. To the best of our knowledge, an abnormal plasma emission spectrum in patients with hereditary aminolevulinate dehydratase deficiency porphyria has never been reported. On the basis of examinations of thousands of plasma emission spectra of patients with acute abdominal pain, either porphyric or not, we can determine that an unstable peak at 404/635 (excitation/emission) nm was found to be exclusive to LP patients. Moreover, the latter phenomenon may also serve to differentiate between LP and an acute attack of hereditary neuroporphyria in general. An emission peak at 621 nm rather than at 635 nm was reported in acute attacks of either coproporphyria (9)(24) or acute intermittent porphyria (24).
In view of the data shown, it is suggested that two biochemical indicators, increased ratio of urinary ALA/PBG and the abnormality in the plasma scan may serve alone or together as indicators of LP. In any case, the diagnosis should always be confirmed by the determination of blood lead. Awareness by porphyria reference laboratories of these two markers can contribute to avoidance of both misdiagnoses of LP and false diagnoses of LP in porphyria patients (25).
Moreover, the quick, inexpensive plasma emission scanning may be used as a screening method for indirect primary diagnosis of lead in workers exposed to lead in the workplace. Further work should be carried out to establish the lead blood concentration at which the spectrum becomes abnormal.
Acknowledgments
The excellent technical assistance of R. Mevasser is gratefully acknowledged. We thank Gloria Ginzach and Charlotte Sachs of the Editorial Board, Rabin Medical Center, Beilinson Campus for their assistance.
References
-aminolevulinic acid dehydratase activity. Clin Chem 1978;24:726-727.-aminolevulinic acid dehydratase of whole blood and the blood lead level. Biochem Med 1973;8:149-159.[Web of Science][Medline]
[Order article via Infotrieve]
-Aminolevulinic acid dehydratase as an index of lead toxicity. Time for a reappraisal?. Eur J Clin Invest 1995;25:53-58.[Web of Science][Medline]
[Order article via Infotrieve]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
