Kidney Week

Abstract: FR-PO0714

A Case of a Pediatric Patient with Minor Glomerular Abnormality and Mild Renal Function Decline Caused by a Novel MAFB Variant

Session Information

• Glomerular Diseases: Membranous Nephropathy, FSGS, and Podocytopathies
  October 23, 2026 | Location: Exhibit Hall A, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Glomerular Diseases

• 1402 Glomerular Diseases: Clinical, Outcomes, and Therapeutics

Authors

• Kumagai, Naonori, Fujita Ika Daigaku, Toyoake, Aichi Prefecture, Japan

Naonori Kumagai, MD, PhD

• Ando, Takuma, Fujita Ika Daigaku, Toyoake, Aichi Prefecture, Japan

Takuma Ando, MD

• Kondo, Tomomi, Fujita Ika Daigaku, Toyoake, Aichi Prefecture, Japan

Tomomi Kondo, MD

• Matsumoto, Yuji, Fujita Ika Daigaku, Toyoake, Aichi Prefecture, Japan

Yuji Matsumoto, MD, PhD

• Sakakibara, Nana, Kobe Daigaku, Kobe, Hyogo Prefecture, Japan

Nana Sakakibara, MD, PhD

• Nozu, Kandai, Kobe Daigaku, Kobe, Hyogo Prefecture, Japan

Kandai Nozu, MD, PhD

• Ikezumi, Yohei, Fujita Ika Daigaku, Toyoake, Aichi Prefecture, Japan

Yohei Ikezumi, MD, PhD

Introduction

MAF bZIP transcription factor B (MAFB) mutations are the cause of Duane syndrome, which is characterized by a congenital eye misalignment, and multicentric carpotarsal osteolysis (MCTO), which is characterized by bone lesions and psychomotor developmental delay. Patients with MAFB mutations develop focal segmental glomerulosclerosis (FSGS) as a complication in Duane syndrome, but is not always present in MCTO, with a case of isolated FSGS also having been reported. Moreover, mutation sites are specific for each disease.

Case Description

A 14-year-old boy was suspected of having stature at the age of 6-year-old. Laboratory findings revealed proteinuria 1+ that was deemed normal. However, at the age of 15, his proteinuria progressed to 2+, which prompted further investigation.
The patient was 150.2 cm (-2.0 SD) tall and weighed 49.8 kg. Neither psychomotor developmental delay nor ocular or bone symptoms were observed. No family history of urinalysis abnormalities, renal disease, or ocular disease was reported. Laboratory findings were as follows: urine protein, 1+; occult blood, -; urine protein/creatinine (Cr) 1.09 g/gCr; Cr, 0.73mg/dL; Cr-eGFR, 81.6ml/min. Renal function decline was observed year after year.
Renal histopathology showed no segmental or global sclerosis of the glomeruli but did reveal very mild interstitial fibrosis. Electron microscopy showed partial disappearance of the foot processes.
Next-generation sequencing analysis revealed a novel in-frame variant in exon 1 of MAFB in a heterozygous manner. This variant has not been reported in healthy control databases, and none of the asymptomatic parents possessed this variant, suggesting a de novo variant. Based on the ACMG criteria, it was classified as likely pathogenic.

Discussion

Nephropathy in the present case may have been caused by a novel MAFB mutation. Although the nephropathy was minor glomerular abnormality, a mild renal function decline had already been observed, suggesting glomerular epithelial cell injury. No symptoms of Duane syndrome and MCTO were observed, with only nephropathy having been present. The site of the MAFB variant differed from those previously reported in Duane syndrome, MCTO, and isolated FSGS. This case highlights the importance of differentiating MAFB mutation in nephropathy and the diversity of clinical symptoms caused by MAFB mutation.