Molecular study of proteinuria in patients treated with B₁₂ supplements: Do not forget megaloblastic anemia type 1

Background/Aims: Current consensus supports the notion that proteinuria is a marker of renal disease with prognostic implications. Whereas most chronic kidney disease patients with proteinuria would often require antiproteinuric agents, there are some exceptions. Megaloblastic anemia type 1 (MGA1) is characterized by megaloblastic anemia due to congenital selective vitamin B ₁₂ malabsorption and proteinuria. In the present study, we describe 2 Israeli Jewish patients with MGA1 and isolated proteinuria. Methods: Because of their origin, the patients were screened for the presence of the already studied Tunisian AMN mutation, by direct sequencing the corresponding region from genomic DNA. PCR products were purified and sequenced. Results: Genomic DNA sequencing of the AMN gene of both patients confirmed that the acceptor splice site in intron 3 was changed from CAG to CGG (208-2A→G). Conclusion: We determined the molecular basis of MGA1 in both patients and discuss the involvement of the cubilin/AMN complex in this pathology and its role in the development of the proteinuria. We also discuss the questionable significance of antiproteinuric treatment for these patients.