CYSTINURIA Research Center for Genetic Engineering and Biotechnology “Georgi D. Efremov”, MASA Important points: Cystinuria is an autosomal recessive disorder that is characterized by an impaired transport of cystine, ornithine, lysine and arginine in the proximal renal tubule and in the epithelial cells of the gastrointestinal tract that leads in an elevated urine concentration of these amino acids. High concentration of cystine in the urinary tract leads to the formation of cystine calculi in the kidneys due to low solubility of cystine in acidic environment. Clinically, cystinuria is divided into two types: Type I cystinuria – heterozygotes have normal excretion of cystine and dibasic amino acids, which implies that the disease is inherited autosomal-recessive, Non-type I cystinuria - heterozygotes shows different levels of urinary hyperexcretion of cystine and dibasic amino acids, which implies that the disease is inherited autosomal-dominant with incomplete penetrance for cystine lithiasis. Genetics / Inheritance pathways: Two genes responsible for cystinuria have been identified: SLC3A1 gene – located on 2p and SLC7A9 gene – located on 19q These genes encodes the subunits of rBAT/b0+AT transporter of cystine and dibasic amino acids. Based to the gene that is affected, cystinuria is divided into: Type A cystinuria – homozygotes/compound heterozygotes for mutation in SLC3A1 gene, Type B cystinuria – homozygotes/compound heterozygotes for mutation in SLC7A9 gene, Type AB cystinuria – one mutation in SLC3A1 gene and one mutation in SLC7A9 gene. This cystinuria type is very rare, and probands manifest as heterozygotes for type B cystinuria. Genetic testing: More than 130 and 90 mutations in SLC3A1 and SLC7A9 genes have been identified, respectively. There are several most common cystinuria mutations in south-eastern European countries. These are T216M, M467T, R365L in SLC3A1 gene and G105R in SLC7A9 gene. Cystinuria mutations are specific for certain ethnic groups. Importance of molecular testing: Determinination of the molecular defect confirms the disease. Determination of cystinuria-carrier status in individuals with a family history of cystinuria enables evaluation of the risk of having child with cystinuria. CYSTINURIA tests performed at RCGEBPrice (МКД) Determining the genetic defect in SLC3A1 gene in patients with cystinuria using DNA sequencing method Determining the genetic defect in SLC7A9 gene in patients with cystinuria using DNA sequencing method Carrier detection in a families with known gene defect Amino acid analysis6.100 References: 1. Online Mendelian Inheritance in Man, No: # и # (Cystinuria type A) и # (Cystinuria type B) 2. Segal, S., Thier, S.O. (1989): Cystinuria, In: The metabolic bases of inherited disease. 6th edition. Edited by Scriver, C. R., Beaudet, A.L., Sly, W. S., Valle, D. New York, McGraw-Hill Book Co International Cystinuria Consortium. (1999): Non-type I cystinuria caused by mutations in SLC7A9, edcoding a subunit (b0,+AT) of rBAT. Nat. Genet., 23, Popovska-Jankovic et al. (2013): Molecular characterization of cystinuria in south-eastern European countires. Urolithiasis, 41(1): Analysеs performed at RCGEB Cystinuria is characterized both on biochemical and genetic level. Amino acid analyses of cystine and dibasic amino acids (lysine, ornithine and arginine) are performed on Biochrom 30 Amino acid analyzer. Determination of the genetic defect responsible for cystinura at RCGEB is performed by sequencing analysis of the SLC3A1 and SLC7A9 genes.. Material for testing Whole blood specimens in sterile tubes with anticoagulant EDTA from the affected child and the parents. Urine samples for amino acid analysis from the affected child and the parents. RCGEB, 2013