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SLC3A1
solute carrier family 3 member 1
SLC3A1 is located on the short (p) arm of chromosome 2, at band 2p21. Arm ratio per GRCh38 - banding schematic.
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Overview
SLC3A1 encodes the heavy subunit of a heteromeric amino acid transporter located predominantly in the kidneys. This transporter plays a critical role in reabsorbing cystine and dibasic amino acids-ornithine, arginine, and lysine-from the glomerular filtrate back into the circulation during urine formation. When pathogenic variants compromise SLC3A1 function, these amino acids accumulate in urine, where cystine can precipitate to form kidney stones.
Cystinuria, the primary condition associated with SLC3A1 pathogenic variants, follows an autosomal recessive inheritance pattern. The gene is included in UK carrier screening panels because identifying carrier status in prospective parents allows informed reproductive choices and early intervention for affected children.
What the gene does
The SLC3A1 protein functions as the heavy chain of a heterodimeric transporter complex that operates in the proximal tubule of the kidney. It partners with a light chain encoded by the SLC7A9 gene to form a functional transporter embedded in the apical membrane of tubular epithelial cells. This complex mediates the reabsorption of cystine, ornithine, arginine, and lysine from the tubular lumen into epithelial cells, preventing their loss in urine.
The heavy subunit stabilises the complex and facilitates its trafficking to the cell membrane, whilst the light chain carries out the actual amino acid translocation. The transporter operates as an obligate exchanger, coupling the uptake of cystine and dibasic amino acids with the export of other neutral amino acids. Under normal physiological conditions, this mechanism ensures minimal urinary excretion of cystine, which is poorly soluble and prone to crystallisation at acidic pH values typical of urine.
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Chromosome location
SLC3A1 is located on the short arm of chromosome 2 at position 2p21. The gene spans approximately 70 kilobases of genomic DNA and comprises ten exons. Its chromosomal position places it in a region that also contains the PREPL gene; large deletions encompassing both genes result in hypotonia-cystinuria syndrome, a contiguous gene deletion disorder with a broader phenotypic spectrum than isolated cystinuria.
Protein structure
The SLC3A1 protein comprises 685 amino acids and contains a disordered region spanning amino acids 1 to 56 at the N-terminus. This N-terminal disordered segment likely contributes to regulatory interactions or post-translational modifications, though its precise functional role has not been fully characterised. Beyond the disordered region, the protein includes transmembrane segments and a large extracellular domain that mediates heterodimerisation with the SLC7A9 light chain through a conserved disulphide bridge. The structural organisation enables the heavy subunit to anchor the transporter complex in the membrane and coordinate amino acid recognition alongside its partner protein.
Key variants
More than 120 pathogenic variants in SLC3A1 have been reported in association with cystinuria. These variants include missense substitutions, nonsense mutations, small insertions or deletions, and splice-site alterations. Many of these genetic changes result in impaired protein folding, defective trafficking to the cell membrane, or reduced amino acid transport activity. Large deletions that remove SLC3A1 in conjunction with neighbouring genes produce more complex phenotypes, such as hypotonia-cystinuria syndrome when PREPL is also deleted.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Pathogenic variants in SLC3A1 cause cystinuria, an autosomal recessive disorder characterised by excessive urinary excretion of cystine and dibasic amino acids. Affected individuals experience recurrent kidney stone formation due to cystine precipitation in urine. Stone episodes often begin in childhood or adolescence and may lead to complications including urinary tract obstruction, infection, and impaired renal function if left unmanaged. The severity of stone disease varies among individuals, influenced by fluid intake, urinary pH, and the specific variant present.
Inheritance pattern
Conditions caused by pathogenic SLC3A1 variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
SLC3A1 is included on several NHS Genomic Medicine Service gene panels relevant to kidney and metabolic disorders. It holds green classification status on the Likely Inborn Error of Metabolism panel (R98), the Nephrocalcinosis or Nephrolithiasis panel (R256), and the Undiagnosed Metabolic Disorders panel. These designations reflect strong evidence supporting the gene's role in kidney stone disease and inborn errors of amino acid metabolism, guiding diagnostic testing strategies within the NHS.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What does it mean to be a carrier of an SLC3A1 variant?
Carriers have one pathogenic SLC3A1 variant and one normal copy of the gene. They typically do not develop cystinuria because one functional gene copy provides sufficient transporter activity. If two carriers have children together, each pregnancy has a 25% chance of inheriting two pathogenic variants and developing the condition.
How is cystinuria managed?
Management focuses on reducing cystine concentration in urine through high fluid intake to maintain dilute urine, dietary modification to limit methionine (a cystine precursor), and urinary alkalinisation to increase cystine solubility. In some cases, medications that bind cystine may be prescribed, and surgical intervention is occasionally required to remove large stones.
Can genetic testing detect all SLC3A1 pathogenic variants?
Standard sequencing identifies most pathogenic variants, including point mutations and small insertions or deletions. However, large deletions or complex rearrangements may require additional testing methods such as deletion-duplication analysis to ensure comprehensive detection.
References
- Chabrol B, Martens K, Meulemans S. Deletion of C2orf34, PREPL and SLC3A1 causes atypical hypotonia-cystinuria syndrome. Journal of medical genetics. 2008. PMID: 18234729
- Martens K, Jaeken J, Matthijs G. Multi-system disorder syndromes associated with cystinuria type I. Current molecular medicine. 2008. PMID: 18781961
- Martens K, Heulens I, Meulemans S. Global distribution of the most prevalent deletions causing hypotonia-cystinuria syndrome. European journal of human genetics : EJHG. 2007. PMID: 17579669
- Font-Llitjós M, Jiménez-Vidal M, Bisceglia L. New insights into cystinuria: 40 new mutations, genotype-phenotype correlation, and digenic inheritance causing partial phenotype. Journal of medical genetics. 2005. PMID: 15635077
- Langman CB. The molecular basis of kidney stones. Current opinion in pediatrics. 2004. PMID: 15021200
- Goodyer P. The molecular basis of cystinuria. Nephron. Experimental nephrology. 2004. PMID: 15499206
- Schmidt C, Vester U, Wagner CA. Significant contribution of genomic rearrangements in SLC3A1 and SLC7A9 to the etiology of cystinuria. Kidney international. 2003. PMID: 14531788
- Fernández E, Carrascal M, Rousaud F. rBAT-b(0,+)AT heterodimer is the main apical reabsorption system for cystine in the kidney. American journal of physiology. Renal physiology. 2002. PMID: 12167606
- Dello Strologo L, Pras E, Pontesilli C. Comparison between SLC3A1 and SLC7A9 cystinuria patients and carriers: a need for a new classification. Journal of the American Society of Nephrology : JASN. 2002. PMID: 12239244