Approach to the Diagnosis of Thin Basement Membrane Nephropathy in Females With the Use of Antibodies to Type IV Collagen.
Alport syndrome can be X-linked, autosomal-recessive, or possibly autosomal-dominant (reviewed in references 3 and 7-10). There are a number of phenotypic variants of AS, and the classic findings of hematuria, progressive renal failure, bilateral high-tone sensorineural hearing loss, and ocular changes are not found in all patients. In the X-linked form, there is a defect in the gene coding for the [Alpha]5 chain of type IV collagen ([Alpha]5[IV]) located on the long arm of chromosome X. Autosomal-recessive patients have mutation(s) in either COL4A3 or COL4A4 genes situated on chromosome 2. These 2 genes code for the [Alpha]3 ([Alpha]3[IV]) and [Alpha]4 ([Alpha]4[IV]) chains of type IV collagen, respectively. Ultrastructurally, the GBM presents alternating areas of thinning and thickening, splitting, lamellation, and granular inclusions in the lamina densa. These so-called pathognomonic findings are not always found in children and females, who may only have thin GBMs without other alterations. Therefore, it may be difficult to make a distinction between TBMN and AS in these patients on a purely morphologic basis.
Thus, the diagnosis of TBMN remains one of exclusion. Although it has been reported that glomeruli of patients with TBMN reveal no abnormalities when stained with antibodies against [Alpha]3(IV), [Alpha]4(IV), and [Alpha]5(IV), these observations have not been published. In the present study, we sought to examine the usefulness of antibodies against [Alpha]1, [Alpha]3, [Alpha]4, and [Alpha]5 chains of type IV collagen in establishing the diagnosis of TBMN in 9 adult female patients with diffusely thin GBMs.
MATERIALS AND METHODS
Patient Selection and Clinical Information
Nine female patients with diffusely thin GBM on renal biopsy were identified between 1994 and 1996 from the surgical pathology files of the University Health Network, Toronto, Ontario. Controls included 1 male patient with known X-linked AS, 1 female patient with immunoglobulin A (IgA) nephropathy, and 2 female patients with minimal-change nephrotic syndrome. Clinical charts of index patients were reviewed for age, indication for renal biopsy, and family history. Clinical follow-up was obtained.
Light, Immunofluorescence, and Electron Microscopy
Renal biopsies were routinely processed for light, immunofluorescence, and electron microscopy. The glass slides were reviewed for all indexed cases and controls. All cases were examined by electron microscopy. The GBM was measured in all cases using the method of harmonic mean of orthogonal intercepts. A measurement of less than 264 nm was required to make a diagnosis of TBMN.
Murine monoclonal antibodies anti-[Alpha]1(IV) (MAB1), anti-[Alpha]3(IV) (MAB3), and anti-[Alpha]5(IV) (MAB5-A7) were purchased from Wieslab AB (Lund, Sweden). The monoclonal antibody against [Alpha]4(IV) (MAB85) was graciously provided by Clifford Kashtan (University of Minnesota, Minneapolis).
Monoclonal antibodies against [Alpha]1(IV) (MAB1), and [Alpha]3(IV) (MAB3) were obtained from mice immunized with the noncollagenous C-terminal domain (NC1) of bovine GBM. The monoclonal antibody against [Alpha]5(IV) (MAB5-A7) was obtained from immunization of mice with the collagenase-resistant residue of human GBM.[13,14] The monoclonal antibody MAB85 (anti-[Alpha]4[IV]) was obtained from mice immunized with human NC1.
Only the MAB85 was diluted 1:1 for immunohistochemistry. The other antibodies were not diluted.
Immunofluorescence for [Alpha]1(IV), [Alpha]3(IV), [Alpha]4(IV), and [Alpha]5(IV) on Frozen Tissue
The slides were stained for [Alpha]1, [Alpha]3, [Alpha]4, and [Alpha]5 chains of type IV collagen according to the method proposed by Yoshioka et al, with slight variation. Briefly, slides were fixed in acetone for 5 minutes. After washing in phosphate-buffered saline, the slides were treated with a solution of 6 mol/L urea, 0.1 mol/L glycine at pH 3.5 for 1 hour at 4 [degrees] C. Incubation with the primary antibodies for 45 minutes at room temperature followed. After a phosphate-buffered saline wash, fluorescein isothiocyanate--conjugated goat anti-mouse antibody (Dako Corporation, Carpinteria, Calif) was applied for 30 minutes. The slides were mounted in a permanent mounting solution (Gelvatol, Air Products and Chemicals, Allentown, Pa). The primary antibody was omitted in negative controls.
The 9 female patients with diffusely thin GBMs were between 23 and 43 years old (average, 34 years) (Table 1). Seven patients presented with microscopic hematuria, with or without low-grade proteinuria; 3 of those patients were identified during assessment for living-related kidney donation. Two patients were being investigated because of proteinuria of 2.0 g/24 h or more.
Table 1. Clinical Summaries of 9 Female Patients Age Patient at Indication for No. Biopsy, y Renal Biopsy Family History 1 42 Microscopic hematuria Two uncles have renal for 3 y failure of unknown etiology; no deafness in family members 2 43 Potential donor for Son has renal failure son; microscopic due to reflux hematuria nephropathy; no other family history 3 36 Microscopic hematuria; Mother, father, proteinuria sister, and maternal (0.4 g/24 h) aunt with hematuria 4 27 Microscopic hematuria; No known family no proteinuria history of hematuria or renal disease 5 37 Potential donor for Father has microscopic brother; microscopic hematuria; brother has hematuria; no end-stage renal proteinuria disease of unknown etiology 6 35 Proteinuria No known family (1.0 g/24 h); history of hematuria microscopic hematuria or renal disease 7 34 Potential donor for Sister with end-stage sister; hematuria renal disease of x 4 y; no proteinuria unknown etiology; maternal aunt has microscopic hematuria 8 23 Proteinuria Brother received (2.97 g/24 h) and kidney transplant at hematuria 40 y, primary disease unknown; 2 brothers and sisters have normal urinalysis 9 27 Increasing proteinuria No family history (2.0 g/24 h at time available; patient of biopsy); hematuria is adopted since age 7 y Patient Length of No. Follow-up Follow-up 1 Normal renal function; 6 mo no changes over time 2 Normal renal function; 4 mo no changes over time 3 Normal renal function; 3 y no changes over time 4 Normal renal function; 3 y no changes over time 5 Normal renal function Nil 6 Normal renal function; 4 y history of goiter 7 Normal renal function; 5 y no changes over time 8 Increasing creatinine 18 mo over time 9 Increasing proteinuria 2.5 y during pregnancy (up to 7 g/24 h); 3 g/24 h postpartum; creatinine normal and stable
A family history of hematuria only was obtained in 1 patient. Two additional patients had a family history that included both hematuria and renal failure of unknown etiology. Another 2 patients had relatives with end-stage renal disease of unknown etiology, and 1 patient had a son diagnosed with reflux nephropathy. There was no known family history of hematuria or renal disease in 3 patients; 1 of these patients had been adopted.
Clinical follow-up was obtained for 8 patients and varied from 4 months to 5 years (average, 26 months). Of the 8 patients for whom follow-up was available, 7 had stable renal function with persistent hematuria and 1 patient had progressive renal insufficiency.
No glomerular changes other than global and/or segmental glomerulosclerosis were observed (Table 2). Global glomerulosclerosis involved less than 10% of glomeruli in 3 patients, and 12% to 30% of glomeruli in 4 patients. Two of those 4 patients also had a few glomeruli with segmental scars (Figure 1). Interstitial fibrosis of moderate severity was seen in only 1 patient (patient 4) and was minimal or mild, and usually focal, in all other patients.
Table 2. Light and Electron Microscopy(*) Electron Microscopy (Features Additional GBM Width Patient to Diffuse Thinning Measurement, No. Light Microscopy of GBM) nm 1 No GS; no other LM Focal mild splitting 204 changes 2 20% global GS; focal None 196 mild IF 3 No GS; focal mild IF None 214 4 30% global GS; focal None 192 mild to moderate IF 5 5% global GS; no Focal mild splitting 161 other LM changes 6 9% global GS; focal None 186 minimal to mild IF 7 5% global GS; no IF None 231 8 20% global GS and Focal mild splitting 239 focal and segmental and rare GS; mild IF intramembranous granular inclusions 9 12% global GS and Focal mild splitting 179 focal and segmental and rare GS; focal minimal IF intramembranous granular inclusions (*) GBM indicates glomerular basement membrane; GS, glomerulosclerosis; LM, light microscopic; and IF, interstitial fibrosis.
Immunofluorescence microscopy was negative for IgG, IgM, IgA, C3, C4, and [Kappa] and [Lambda] light chains in all cases.
Immunofluorescence with antibodies against [Alpha]1(IV), [Alpha]3(IV), [Alpha]4(IV), and [Alpha]5(IV) (Table 3) showed diffuse and strong linear staining along GBM in 7 patients (Figure 2); this pattern was similar to that seen in positive controls (Figure 2). Patients 2 and 9 demonstrated segmental staining of GBM with [Alpha]3, [Alpha]4, and [Alpha]5 chains of type IV collagen (Figure 2). Of those 2 patients, only patient 9 exhibited diffuse and strong linear staining for [Alpha]1(IV) (Figure 3). Weak and uneven staining for [Alpha]1(IV) was observed in the biopsy from patient 2. Staining for [Alpha]3, [Alpha]4, and [Alpha]5 chains of type IV collagen was lacking altogether in the male patient with X-linked AS. Diffuse and strong linear staining for [Alpha]1(IV) was present in that patient (results not shown).
Table 3. Immunofluorescence With Antibodies Against [Alpha]1, [Alpha]3, [Alpha]4, and [Alpha]5 Chains ([Alpha]1[IV],[Alpha]3[IV], [Alpha]4[IV], and [Alpha]5[IV], respectively) of Type IV Collagen(*) Patient [Alpha]1 [Alpha]3 [Alpha]4 [Alpha]5 No. (IV) (IV) (IV) (IV) 1 D D D D 2 S (weak) S S S 3 D D D D 4 D D D D 5 D D D D 6 D D D D 7 D D D D 8 D D D D 9 D S S S (*) D indicates diffuse staining, as controls; S, segmental staining.
In all cases, the mesangial matrix was either normal or mildly increased and did not contain electron-dense immune-type deposits (Table 2). Effacement of foot processes of glomerular visceral epithelial cells was noted over short segments. There was diffuse thinning of GBM that was confirmed by measuring orthogonal intercepts (Figure 4). The GBM measurement in indexed patients ranged from 161 to 239 nm (average, 200 nm), as opposed to controls, in which the GBM measured from 296 to 322 nm (average, 309 nm). The GBM of the male patient with AS measured 324 nm and presented typical changes of AS (namely, alternating areas of thin and thick GBM with splitting, lamellation, and granular inclusions). Similar changes were seen focally in only 1 indexed patient (Figure 5, A). Changes limited to splitting of short segments of GBM were seen in 3 cases (Figure 5, B). Notably, splitting of GBM over short segments was also seen in 2 cases of minimal-change nephrotic syndrome, and 1 case of IgA glomerulopathy.
A pathologist confronted with a renal biopsy in which diffuse GBM thinning is the predominant anomaly has to take numerous steps to try to establish an accurate diagnosis. In an attempt to rule out AS, one must, if possible, obtain a complete clinical summary, including a detailed family history, and perform electron microscopy and immunofluorescence with antibodies against [Alpha]3, [Alpha]4, and [Alpha]5 of type IV collagen.
Unfortunately, a detailed family history might be unobtainable; for example, patient 9 in our study was adopted. If and when available, the family history might be of limited use in some patients because of the possibility of a new mutation or because the etiology of renal failure in relatives is undetermined. Four patients in our study had relatives with renal failure of unknown origin. Furthermore, in a retrospective study like ours, and often in the practice of renal pathology, a complete clinical history cannot be obtained.
Electron microscopy cannot discriminate between TBMN and AS in patients in whom only a diffusely thin GBM with minimal alterations of the lamina densa is found. Any degree of GBM splitting or lamellation is compatible with AS, even if the GBM changes are mild and present over short segments only. Conversely, such changes are not pathognomonic for AS and can be found in other renal diseases, including TBMN. Among the 4 patients in our study with segmental splitting of GBM by electron microscopy (patients 1, 5, 8, and 9), only 1 patient (patient 9) had segmental GBM staining for [Alpha]3, [Alpha]4, and [Alpha]5 chains of type IV collagen by immunofluorescence. This pattern of staining is likely specific for the diagnosis of AS, but in the absence of other corroborative evidence (no stigmata of AS and no family history), only genetic analysis would give a definitive diagnosis. Another patient (patient 2), also with segmental GBM staining (but no GBM splitting), lacked clinical indices supporting a diagnosis of AS, including a family history compatible with AS. The absence of strong staining with [Alpha]1 of type IV collagen in that patient indicates that the GBM antigens are not well preserved, and that the segmental staining observed with [Alpha]3(IV), [Alpha]4(IV), and [Alpha]5(IV) is probably spurious. This case illustrates the need to perform adequate controls and to interpret the results with caution. Interestingly, the remaining 3 patients with segmental splitting of the GBM but with normal GBM staining with [Alpha]3, [Alpha]4, and [Alpha]5 chains of type IV collagen all have male relatives with end-stage renal disease of unknown etiology. In these 3 patients, normal GBM staining does not exclude AS or the carrier status of the Alport mutation. Favorable lyonization may result in a normal pattern of staining in females with X-linked AS. Another possibility is that these patients are heterozygous for the mutation associated with autosomal-recessive AS (see below). Furthermore, some patients with AS have normal staining with antibodies against [Alpha]3, [Alpha]4, and 5 chains of type IV collagen. Genetic studies could help sort out the likely pattern of inheritance of renal disease in these 3 families.
Four patients (patients 3, 4, 6, and 7) demonstrated no ultrastructural GBM abnormalities other than diffuse thinning; all had a normal pattern of GBM staining by immunofluorescence. It is likely that these patients have TBMN. Of these 4 patients, 2 reported a family history of hematuria. Hematuria tends to be underreported unless family members are tested specifically. Renal function has remained normal and stable in these 4 patients during an average follow-up of 3.75 years, although patient 7 has a sister with end-stage renal disease of unknown etiology. In the family of this patient, the possibility of autosomal-recessive AS has to be considered. Presumably, patient 7 would be heterozygous for the mutant gene (see below). In contrast, an extensive family history of hematuria would suggest TBMN with an autosomal dominant pattern of inheritance in patient 3.
The putative protein defect in GBM of patients with TBMN remains unknown (reviewed in references 3 and 4). Based on linkage analysis studies, Lemmink et al and others have proposed that patients with TBMN might be heterozygous for the mutant gene that causes autosomal-recessive AS. Their findings would tend to support the hypothesis that TBMN and AS are entities belonging to the same spectrum of disease, although others have not been able to demonstrate a similar association. Arguing against such a hypothesis is the fact that Nomura and his colleagues reported no hematuria on repeated testing of heterozygous parents of a patient with autosomal-recessive AS. Furthermore, in 3 animal models of autosomal-recessive AS, heterozygous animals have a normal phenotype. Thin GBM nephropathy is believed by some to have an autosomal-dominant pattern of inheritance.[3,4] The issue remains unresolved. In our study, no abnormality of [Alpha]3(IV), [Alpha]4(IV), or [Alpha]5(IV) could be demonstrated by immunofluorescence in 7 patients. Possibly, this method lacks sensitivity for the detection of small quantitative changes.
A more contentious issue is whether patients with TBMN should be considered for kidney donation. The long-term prognosis of patients thought to have TBMN is unknown. While a benign outcome is the rule, glomerular obsolescence, hypertension, and proteinuria have been reported.[5,6] It is important to note that the studies reporting progression toward renal insufficiency in TBMN might have unknowingly included unidentified AS patients. It has been suggested that in patients with a presumed diagnosis of TBMN, only a detailed family history reporting several male members with long-standing hematuria and no progression toward renal failure in advanced age is the best evidence for a benign diagnosis. Follow-up was too short for most of the patients included in our study to allow prognostication about renal outcome.
Thin GBM in female patients presents a common diagnostic puzzle in the practice of renal pathology. There is much overlap between TBMN and AS, especially in female patients. Our discussion emphasizes the need to correlate clinical history and pathologic findings in the interpretation of renal biopsies. The addition of immunofluorescence for [Alpha]1, [Alpha]3, [Alpha]4, and [Alpha]5 chains of type IV collagen might be useful in confirming a diagnosis of AS in patients in whom there is a documented family history. In other patients, abnormalities of GBM staining might raise the degree of suspicion for that diagnosis. In our study, patients presumed to have TBMN did not have detectable defects of [Alpha]3, [Alpha]4, and [Alpha]5 chains of collagen type IV in the GBM. Normal GBM staining, however, does not exclude AS or the carrier status of the Alport mutation; the family history of 4 of our patients with normal GBM staining was suggestive of AS.
Studies of families with suspected TBMN are needed to determine the pattern of inheritance of this disorder. There are possibly at least 2 groups of patients; the first group might be heterozygous carriers of the mutant gene for autosomal-recessive AS, while in others TBMN might be inherited as an autosomal-dominant disease.
This study has been funded in part by the University Health Network Pathology Associates and by the University Health Network Department of Pathology, Toronto, Ontario.
The author thanks Clifford Kashtan, MD, for his generous gift of the MAB85 antibody and recognizes the excellent technical assistance of Richard Leung, BSc, ART (electron microscopy and photography) and Joanne Mariano, BSc, MLT (immunofluorescence).
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Accepted for publication December 7, 2000.
From the Department of Laboratory Medicine and Pathobiology, Toronto General Hospital, University Health Network, University of Toronto, Ontario.
Reprints: Ginette Lajoie, MD, FRCPC, Department of Pathology, Eaton Wing 4-323, Toronto General Hospital, University Health Network, 200 Elizabeth St, Toronto, Ontario, M5G 2C4 Canada (e-mail: email@example.com).
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|Publication:||Archives of Pathology & Laboratory Medicine|
|Date:||May 1, 2001|
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