The COL4A3 and COL4A4 Digenic Mutations in cis Result in Benign Familial Hematuria in a Large Chinese Family

Clinical Features and Familial Mutations in an Autosomal-Inherited Alport Syndrome Patient With the Presentation of Nephrotic Syndrome

Background: The aim of this study was to report the clinical features and mutations in a patient with autosomal-inherited Alport syndrome (AS). Methods: We examined the clinical data, mutation analysis results, and family tree of a patient with autosomal-inherited AS, who had nephrotic syndrome as her first manifestation. Results: The proband was a girl of 11 months who presented with nephritic and nephrotic syndromes including gross hematuria but had a normal renal function. Her treatment course was complicated by steroid resistance and a poor response to cyclosporine A and cyclophosphamide pulse therapy. Renal biopsy was performed 2 years after disease onset; light microscopy showed glomerular segmental mesangio-proliferative lesions, and type IV collagen staining showed the loss of the α3 chain in the glomerular and tubular basement membrane (GBM and TBM) and α5 chain loss in the GBM. Electron microscopy showed uneven GBM thickness, with the dense basement membrane (BM) layer obviously delaminated and torn, showing a typical "lace-like" change. The segmental BM was loosened and widened. Her father did not develop microscopic hematuria until 10 years later, while her grandmother had asymptomatic hematuria and proteinuria when the proband was diagnosed. We detected a new COL4A4 mutation in the proband, namely c.1715delG (p.G572Vfs ^* 81) in exon 24. Her father and grandmother carried the same mutation, but her mother and sister did not. Conclusions: We found a new potentially pathogenic mutation of COL4A4 in a patient with autosomal-inherited AS, which presented as nephrotic syndrome in infancy.

Prevalence of clinical, pathological and molecular features of glomerular basement membrane nephropathy caused by COL4A3 or COL4A4 mutations: a systematic review

BACKGROUND

Patients heterozygous for COL4A3 or COL4A4 mutations show a wide spectrum of disease, extending from familial isolated microscopic haematuria, as a result of thin basement membranes (TBMs), to autosomal dominant Alport syndrome (ADAS) and end-stage renal disease (ESRD). Many patients are mentioned in the literature under the descriptive diagnosis of TBM nephropathy (TBMN), in which case it actually describes a histological finding that represents the carriers of autosomal recessive Alport syndrome (ARAS), a severe glomerulopathy, as most patients reach ESRD at a mean age of 25 years.

METHODS

We performed a systematic literature review for patients with heterozygous COL4A3/A4 mutations with the aim of recording the spectrum and frequency of pathological features. We searched three databases (PubMed, Embase and Scopus) using the keywords 'Autosomal Dominant Alport Syndrome' OR 'Thin Basement Membrane Disease' OR 'Thin Basement Membrane Nephropathy'. We identified 48 publications reporting on 777 patients from 258 families.

RESULTS

In total, 29% of the patients developed chronic kidney disease (CKD) and 15.1% reached ESRD at a mean age of 52.8 years. Extrarenal features and typical Alport syndrome (AS) findings had a low prevalence in patients as follows: hearing loss, 16%; ocular lesions, 3%; basement membrane thickening, 18.4%; and podocyte foot process effacement, 6.9%. Data for 76 patients from 54 families emphasize extensive inter- and intrafamilial heterogeneity, with age at onset of ESRD ranging between 21 and 84 years (mean 52.8).

CONCLUSIONS

The analysis enabled a comparison of the clinical course of patients with typical ARAS or X-linked AS with those with heterozygous COL4A mutations diagnosed with TBMN or ADAS. Despite the consequence of a potential ascertainment bias, an important outcome is that TBM poses a global high risk of developing severe CKD, over a long follow-up, with a variable spectrum of other findings. The results are useful to practicing nephrologists for better evaluation of patients.

A Novel Heterozygous Mutation of the COL4A3 Gene Causes a Peculiar Phenotype without Hematuria and Renal Function Impairment in a Chinese Family

Mutations in the COL4A3 gene are frequently reported to be associated with various types of hereditary nephropathy. COL4A3 encodes the α3 chain of type IV collagen, which is the main structural protein in the basement membrane. Mutations in this gene are always related to kidney performance, and deafness and ocular lesion have also been reported. In this study, using next-generation sequencing, we investigated the DNA of a family visiting a clinic for hearing loss. A new missense mutation was found in COL4A3 of 5 patients, c.3227C>T (p.P1076L). Based on these results, we predict that the mutation is pathogenic and leads to abnormal collagen IV. Here, we report for the first time on this autosomal dominant syndrome, characterized by hearing loss and eye abnormalities, but without renal damage, in all carriers. Since the oldest patient in the trial was less than 50 years old, however, we recommend that renal examination be reviewed regularly. Our results reveal expansion in the mutation spectrum of the COL4A3 gene and phenotypic spectrum of collagen IV disease. Our study suggests that next-generation sequencing is an economical and effective method and may help in the accurate diagnosis and treatment of these patients.