# Characteristics of pediatric-onset anti-contactin1 antibody-associated autoimmune nodopathies with concomitant membranous nephropathy

## TL;DR

A rare autoimmune disorder affecting children, linked to nerve and kidney issues, is studied through a new case and literature review.

## Contribution

First detailed report of pediatric-onset CNTN1-AN with membranous nephropathy and a global literature review of six confirmed pediatric cases.

## Key findings

- Pediatric CNTN1-AN is rare, with renal involvement observed in 3/7 cases and MN confirmed in two.
- Neurological symptoms improved with low-dose rituximab, but renal issues often require stronger treatment.
- Pediatric and adult CNTN1-AN cases show similar clinical features but differ in incidence rates.

## Abstract

Anti-contactin-1 antibody-associated autoimmune nodopathy (CNTN1-AN) is a rare disorder predominantly affecting older individuals, characterized by sensorimotor peripheral neuropathy, with over 50% of cases presenting with proteinuria and membranous nephropathy (MN). Pediatric-onset CNTN1-AN is exceptionally rare, and its clinical profile remains poorly characterized.

We report a pediatric case of CNTN1-AN with MN and conduct a literature review to elucidate the pathogenesis and clinical features of CNTN1-AN combined with MN in children. The patient, an 11-year-old girl, presented with a one-month history of progressive lower limb weakness and a 10-day progression of gait instability. Physical examination demonstrated bilateral proximal lower limb weakness, restricted mobility, and sensory abnormalities.No facial or limb edema or frothy urine was observed. Elevated anti-CNTN1 antibody titers were detected in both serum (1:320) and cerebrospinal fluid (CSF) (1:3.2). Urinalysis showed significant proteinuria (4+). Electromyography (EMG) indicated peripheral nerve involvement, and lumbosacral and brachial plexus magnetic resonance imaging (MRI) demonstrated nerve root edema and thickening. Renal biopsy confirmed stage I MN, establishing the diagnosis of CNTN1-AN with MN. Following prednisone and rituximab therapy, motor function improved, though renal progression persisted. A comprehensive literature review identified six confirmed pediatric CNTN1-AN cases globally. Including the current case, renal involvement was observed in 3/7 pediatric cases, with MN confirmed in two. Comparative analysis indicates that CNTN1-AN manifests similarly across pediatric and adult populations, though pediatric cases demonstrate potentially lower incidence rates.

Pediatric CNTN1-AN exhibits a low incidence, requiring ongoing renal function monitoring in affected cases. In CNTN1-AN with MN, neurological symptoms respond well to low-dose rituximab, whereas renal manifestations often require intensified regimens. The mechanisms linking CNTN1-AN and MN remain elusive, highlighting the need for further studies to optimize rituximab therapeutic protocols.