How does LAMB2 contribute to kidney disease? Insights from a pediatric case

We present the case of an 11-year-old girl who has been followed for the past four years after the incidental discovery of asymptomatic microhematuria during school enrollment. Over the course of follow-up, glomerular-origin microhematuria persisted, and mild proteinuria developed and persisted for over six months. This prompted the need for a kidney biopsy. Light microscopy revealed normal kidney tissue, and immunofluorescence findings were negative. However, electron microscopy demonstrated significant variation in glomerular basement membrane (GBM) thickness, with focal splitting. A diagnosis of Alport syndrome was initially suspected, but genetic testing for collagen IV mutations (COL4A3, COL4A4, COL4A5) did not support this diagnosis. Instead, a variant in the LAMB2 gene (c.5039 C > T, p.Ala1680Val) was identified. The variant has not been previously described in the literature but is listed in ClinVar as a variant is of uncertain significance (VUS) and may be associated with the GBM abnormalities observed, leading to the persistent hematuria and proteinuria. Over a one-year follow-up period, the patient has maintained normal renal function without significant proteinuria or hypertension, with only persistent microhematuria. Given the uncertain long-term outcome and the potential impact of the LAMB2 variant on renal function, regular nephrological monitoring remains essential to detect and manage any progression to end-stage renal disease.