Molecular genetics of familial hematuric diseases

Whole exome sequencing reveals novel COL4A3 and COL4A4 mutations and resolves diagnosis in Chinese families with kidney disease

Background

Collagen IV-related nephropathies, including thin basement membrane nephropathy and Alport Syndrome (AS), are caused by defects in the genes COL4A3, COL4A4 and COL4A5. Diagnosis of these conditions can be hindered by variable penetrance and the presence of non-specific clinical or pathological features.

Methods

Three families with unexplained inherited kidney disease were recruited from Shanghai, China. Whole exome sequencing (WES) was performed in the index case from each family and co-segregation of candidate pathogenic mutations was tested by Sanger sequencing.

Results

We identified COL4A4 missense variants [c.G2636A (p.Gly879Glu) and c.C4715T (p.Pro1572Leu)] in the 21-year-old male proband from family 1, who had been diagnosed with mesangial proliferative nephropathy at age 14. COL4A4 c.G2636A, a novel variant, co-segregated with renal disease among maternal relatives. COL4A4 c.C4715T has previously been associated with autosomal recessive AS and was inherited from his clinically unaffected father. In family 2, a novel COL4A3 missense mutation c.G2290A (p.Gly997Glu) was identified in a 45-year-old male diagnosed with focal segmental glomerulosclerosis and was present in all his affected family members, who exhibited disease ranging from isolated microscopic hematuria to end stage renal disease (ESRD). In family 3, ESRD occurred in both male and females who were found to harbor a known AS-causing COL4A5 donor splice site mutation (c.687 + 1G > A). None of these variants were detected among 100 healthy Chinese individuals.

Conclusion

WES identified 2 novel and 2 known pathogenic COL4A3/COL4A4/COL4A5 mutations in 3 families with previously unexplained inherited kidney disease. These findings highlight the clinical range of collagen IV-related nephropathies and resolved diagnostic confusion arising from atypical or incomplete clinical/histological findings, allowing appropriate counselling and treatment advice to be given.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2369-15-175) contains supplementary material, which is available to authorized users.

Clinicopathological analysis of 155 patients with persistent isolated hematuria

OBJECTIVES

To reveal etiologies of persistent isolated hematuria (PIH) through ultrastructural pathological examination, to disclose clinicopathological correlation in cases with PIH, and to summarize appropriate management of patients with PIH.

METHODS

we retrospectively studied 155 PIH patients receiving renal biopsy between January, 2003 and December, 2008 in Peking Union Medical College Hospital. All the clinical data and follow-up result were analyzed.

RESULTS

All subjects included 38 children and 117 adults, with mean age of 11.38±3.25 years for children and 35.17±8.44 years for adults. Thin basement membrane nephropathy (TBMN) was the most common pathology (55.3% of children and 49.6% of adults), followed by IgA nephropathy (18.4% of children and 32.5% of adults, mainly grade 2-3) and mesangial proliferative glomerulonephritis (MsPGN) without IgA deposition (13.2% of children and 12.8% of adults). Besides, Alport syndrome (2.6% of children) and membrane nephropathy (2.6% of children and 0.9% of adults) were demonstrated as other causes of PIH. Elevated mean arteral pressure or protein excretion rate, as well as episodic macrohematuria, indicated higher risk for MsPGN rather than TBMN. On the other hand, severity of microhematuria was irrelevant to pathological types of PIH. Totally, 86 patients were followed up and 37 cases therein stayed on track for long term (mean duration 41.11?28.92 months, range 8-113 months). Most cases had benign clinical course except 3 cases with TBMN, 5 cases with IgA nephropathy, 1 case with MsPGN (without IgA deposition), and 1 case with Alport syndrome, who developed hypertension or proteinuria. All of them were administered timely intervention.

CONCLUSIONS

Close follow-up should be required as the primary management for PIH. Equally important is careful monitoring for early identification of undesirable predictors; while renal biopsy and other timely intervention are warranted if there is hypertension, significant proteinuria or renal impairment.

Familial haematuria: when to consider genetic testing

Haematuria is a common finding in children. It is important to identify the underlying cause whenever possible so that appropriate follow-up is organised, particularly if the child is at risk of developing renal impairment or renal failure in later life. Until recently nephrologists relied on renal biopsy with examination under the electron microscope to make a diagnosis, but genetic testing can often provide an answer, together with additional information about the pattern of inheritance, which is also useful for other family members.

Multiple kidney cysts in thin basement membrane disease with proteinuria and kidney function impairment

Background

Some patients with thin basement membrane disease (TBMD) develop proteinuria, hypertension and different degrees of CKD, besides the persistent microhaematuria characteristic of the disease. Little is known about factors associated with this unfavourable outcome.

Methods

We reviewed clinical, pathological and radiological features of 32 patients with biopsy-proven TBMD. Patients were divided in two groups: those with persistent normal kidney function and negative or minimal proteinuria (n = 16) and those with persistent proteinuria >0.5 g/day (n = 16).

Results

Patients with proteinuria had a worse kidney function at baseline than those with negative proteinuria. Global or segmental glomerulosclerosis, together with interstitial fibrosis, was found in 37% of patients with proteinuria. All proteinuric patients were treated with renin–angiotensin system blockers. At the end of follow-up (198 months in proteinuric patients and 210 months in patients with negative proteinuria) the prevalence of hypertension was 68% in proteinuric patients (12% at baseline), compared with 12 and 6%, respectively, in non-proteinuric patients. A slow decline of renal function was observed in proteinuric patients, although no patient developed end-stage kidney disease. Ultrasound studies showed bilateral kidney cysts in nine patients (56%) with proteinuria. Cysts were bilateral and countless in six patients, and bilateral but with a limited number of cysts in the three remaining patients. No cysts were found in patients with negative proteinuria.

Conclusions

Some patients with TBMD develop hypertension, proteinuria and CKD. Multiple bilateral kidney cysts were found in a majority (56%) of these patients. Further studies are needed to investigate the pathogenesis and the influence on long-term outcome of this TBMD-associated multiple kidney cysts.