C1q nephropathy: a pediatric clinicopathologic study.

Area of Science:

• Nephrology
• Immunopathology
• Pediatric Nephrology

Background:

• Proteinuria and nephrotic syndrome in children can have diverse underlying causes.
• Minimal change disease (MCD) is a common cause of nephrotic syndrome in children, typically responding well to steroids.
• Distinguishing MCD from other glomerular diseases is crucial for appropriate management.

Purpose of the Study:

• To investigate the histological and immunopathological features of childhood nephrotic syndrome with prominent mesangial C1q deposits.
• To determine the clinical course and response to steroid therapy in these patients.

Main Methods:

• Analysis of kidney biopsies from 15 children with proteinuria.
• Histological examination using light microscopy.
• Immunofluorescence (IF) microscopy to detect immune deposits.
• Ultrastructural examination using electron microscopy.

Main Results:

• Fifteen children presented with nephrotic-level proteinuria.
• No glomerular histologic alterations were seen in 8 cases; focal and segmental scarring was present in 7.
• All cases showed prominent mesangial C1q deposits on IF, with variable immunoglobulins.
• Electron microscopy revealed conspicuous mesangial electron-dense deposits in most cases.
• Cases without glomerular histologic alterations were indistinguishable from MCD on light microscopy but showed poor response to prednisone.
• Cases with C1q deposits uniformly had an unsatisfactory response to oral prednisone.

Conclusions:

• The presence of prominent mesangial C1q deposits identifies a subset of childhood nephrotic syndrome.
• This subset may be histologically similar to MCD but exhibits steroid resistance.
• C1q deposition is a key marker for identifying these steroid-resistant cases, regardless of light microscopic findings.