Confocal microscopy of the skin in the diagnosis of X-linked Alport syndrome

Usefulness of skin immunofluorescence for distinguishing SLE from SLE-like renal lesions: a pilot study

Lupus nephritis (LN) may represent a diagnostic problem, particularly in pediatric patients that present with typical histological lesions but do not fulfill the American Rheumatism Association (ARA) criteria for the diagnosis of systemic lupus erythematosus (SLE). Based on the well-described deposition of immunoglobulins (Ig) and complement at the dermoepithelial junction in SLE, we hypothesized that skin biopsies may help in the diagnosis of LN. To test this hypothesis, we carried out a pilot study, performing a skin biopsy in 22 patients with LN and 13 patients with lupus-like lesions, regardless of the time elapsed from onset of renal disease. The latter group of patients was further divided into a purely renal group, designated as isolated full-house nephropathy (FHN), and a dubious cases group, presenting with additional clinical and biological features consistent with SLE but insufficient for diagnosing SLE. None of the 6 isolated FHN patients had positive skin immunofluorescence. Conversely, 5/7 patients in the dubious cases group (p<0.02) and 13/22 in the LN group (p<0.002) had positive staining for C1q, and 5/7 patients in the dubious cases group (p<0.02) and 16/22 patients in the LN group (p<0.001) had positive staining for IgM. No correlation was observed with the time elapsed from the initial diagnosis. These data suggest that skin biopsies may help distinguishing LN from isolated FHN. In addition, they identify an intermediate group of patients with evidence of systemic involvement despite the absence of a sufficient number of ARA criteria to be labeled as SLE.

Deletion 2q36.2q36.3 with multiple renal cysts and severe mental retardation

Interstitial 2q36 deletion is a rare event. We report on a patient with a de novo del(2)(q36.2q36.3) interstitial deletion of the long arm of chromosome 2 diagnosed by classical banding. The phenotype comprised facial dysmorphism, enlarged kidneys with multiple renal cysts, abnormal minora labia, asymmetric lower limbs with dysplastic patella, and severe mental retardation. By physical mapping, using array-comparative genomic hybridisation (CGH) confirmed by Fluorescent In Situ Hybridisation (FISH), the breakpoints of the deletion were mapped and the size of the deletions was measured: 5.61+/-0.19Mb. A skin biopsy was analysed using electronic microscopy showing an alteration of the structure and organisation of the dermal and peri-neuronal basement membrane. The relation between the phenotype and the deletion of both COL4A4 and COL4A3 genes, located in 2q36.3 loci, as well as the disruption of TRIP12 were discussed.

[Collagen alpha5 and alpha2 (IV) chain coexpression: The procedure of choice to diagnose Alport syndrome from skin biopsies]

We describe a simple procedure to use skin biopsies for the diagnosis of Alport syndrome. The technique is based on the co-detection of alpha5 and alpha2 chains of collagen IV along the basal lamina of epidermis through an immunfluorescence technique. Eighty-five per cent of the cases of Alport syndrome are due to a mutation in the gene COL4A5, located on chromosome X, encoding the alpha5 chain of collagen IV. In this situation, the tissue expression of alpha5 chain is abnormal; in males, the absence of expression of alpha5 chain is pathognomonic for Alport syndrome; in females, the expression of alpha5 chain may be discontinuous because of X inactivation. The alpha2 chain is used as a positive control. We have studied skin biopsies from 55 patients (35 females, 20 males) with a suspicion of Alport syndrome, along with five controls. Immunofluorescence was performed on frozen tissue samples; for lecture, epifluorescence and confocal microscopy were compared. In controls, both chains were co-detected. In nine males out of 20, the expression of alpha5 was undetectable; it was preserved in the remaining cases. In female patients, the expression was discontinuous in 16 cases and undetectable in one. There was no difference in sensitivity between the two microscopic techniques. The co-detection of alpha5 and alpha2 chains of collagen IV in frozen skin biopsies is therefore proposed as a simple technique to diagnose Alport syndrome, but requires a good knowledge of the conditions of interpretation.

Collagen α5 and α2(IV) chain coexpression: Analysis of skin biopsies of Alport patients

Alport syndrome is a collagen type IV disease caused by mutations in the COL4A5 gene with the X-linked form being most prevalent. The resultant alpha5(IV) collagen chain is a component of the glomerular and skin basement membranes (SBMs). Immunofluorescent determination of the alpha5(IV) chain in skin biopsies is the procedure of choice to identify patients. In 30% of patients, however, the mutant protein is still found in the SBM resulting in a normal staining pattern. In order to minimize or eliminate false results, we compared the distribution of the alpha2(IV) chain (another SBM component) and the alpha5(IV) chain by standard double label immunofluorescence (IF) and by confocal laser scanning microscopy. The study was performed on 55 skin biopsies of patients suspected of Alports and five normal control specimens. In normal skin, IF showed the classical linear pattern for both collagens along the basement membrane. Additionally, decreased alpha5(IV) was found in the bottom of the dermal papillary basement membrane. Confocal analysis confirmed the results and show alpha5(IV) focal interruptions. In suspected patients, both techniques showed the same rate of abnormal alpha5(IV) expression: segmental in women and absent in men. Our results show a physiological variation of alpha5(IV) location with focal interruptions and decreased expression in the bottom of the dermal basement membrane. Comparison of alpha5(IV) with alpha2(IV) expression is simple and eliminates technical artifacts.

Nephrocystin and ciliary defects not only in the kidney?

Cystoproteins have been recognized to play a major role in the development of cystic kidney diseases (CKDs) via interaction with the cilia/centrosome complex. We highlight our present knowledge on nephrocystin as the defective protein in nephronophthisis type I. Nephrocystin has been localized to the ciliary transition zone not only of renal tubule cells but also of respiratory and retinal cilia. Thus, multi-system involvement as in Senior-Løken-syndrome (retinal degeneration plus nephronophthisis) can be explained by a functional ciliary defect in various tissues. In addition, we illustrate that ciliated respiratory cells have a high potential for diagnostics in CKDs and will further aid understanding of the underlying molecular mechanisms.

Quantitative analysis of type IV collagen subchains in the glomerular basement membrane of patients with Alport syndrome with confocal microscopy

BACKGROUND

Alport syndrome (AS) is an inherited nephropathy characterized by glomerular basement membrane (GBM) abnormalities due to mutations in the type IV collagen genes. Through immunofluorescence analysis, the absence of alpha3(IV), alpha4(IV) and alpha5(IV) chains within the GBM has been shown in the majority of AS cases. In some atypical AS cases, however, staining of the GBM with antibodies against the alpha3(IV), alpha4(IV) and alpha5(IV) chains appeared normal. In this study, we studied these atypical AS cases by quantitative analysis of the expression of type IV collagen subchains in GBM.

METHODS

Twelve patients diagnosed with AS, yet having normal staining for alpha3(IV) and alpha5(IV) chains in the GBM, were recruited. Quantitative analysis of type IV collagen subchains in the GBM was performed using confocal microscopy and immunofluorescence double label techniques.

RESULTS

The absolute amounts of alpha3(IV), alpha4(IV) and alpha5(IV) were significantly lower in AS patients than that in normal subjects, associated with up-regulated expression of type IV collagen in GBM. It was found that eight cases had decreased ratios of alpha3(IV)/IV, alpha4(IV)/IV and alpha5(IV)/IV in the GBM simultaneously; one had reduced levels of alpha3(IV)/IV and alpha5(IV)/IV but had a normal level of alpha4(IV)/IV, and one had reduced alpha3(IV)/IV with normal alpha4(IV)/IV and alpha5(IV)/IV levels. The remaining two patients had normal ratios of alpha3(IV)/IV, alpha4(IV)/IV and alpha5(IV)/IV.

CONCLUSIONS

Confocal analysis demonstrated for the first time that the ratios of alpha3(IV)/IV, alpha4(IV)/IV and alpha5(IV)/IV in the GBM decreased in patients with AS, even though routine immunofluorescence staining for alpha(IV) chains appeared normal. This result not only sheds light on the pathogenesis of AS, but also provides an alternative approach to diagnose atypical AS cases.