A mouse model of type B cystinuria due to spontaneous mutation in FVB/NJcl mice

Cystinuria is an autosomal metabolic disorder caused by mutations in the SLC3A1 and SLC7A9 genes, encoding the amino acid transporter proteins rBAT and b(0,+)AT, respectively. Based on the causative gene, cystinuria is classified into 3 types: type A (SLC3A1), type B (SLC7A9), and type AB (SLC3A1 and SLC7A9). Patients with cystinuria exhibit hyperexcretion of cystine and dibasic amino acids in the urine and develop cystine crystals due to its low solubility in the urine, often resulting in calculus formation. In this study, we present an inbred strain FVB/NJcl mice affected with cystinuria. In the affected mouse kidney, Slc7a9 expression was completely abolished because of a large sequence deletion in the promoter region of the Slc7a9 mutant allele. Slc7a9-deficient mice with FVB/NJcl genetic background developed cystine calculi in the bladder with high penetrance, as compared to the previously reported mouse models of cystinuria. This model may be useful to understand the determinants of crystal aggregation, affecting calculus formation.