rs11854484 — SLC28A2 SLC28A2 Pro22Leu

SLC28A2 Pro22Leu — The Ribavirin Transporter Variant and Anemia Risk

Every dose of ribavirin you swallow must cross the intestinal wall before it can reach the bloodstream, and the protein doing most of that work is CNT2¹¹ CNT2
Concentrative Nucleoside Transporter 2, a sodium-coupled symporter expressed on the apical (luminal) membrane of jejunal enterocytes that preferentially transports purine nucleosides — including ribavirin — against their concentration gradient, driven by the intestinal sodium electrochemical gradient, encoded by SLC28A2 on chromosome 15q21.1. The rs11854484 variant changes a proline to leucine at position 22 of this transporter, altering how efficiently it accumulates ribavirin in the enterocyte and, downstream, how much drug ends up trapped in red blood cells.

The Mechanism

rs11854484 sits at GRCh38 position chr15:45,253,279 (NC_000015.10) within the coding sequence of SLC28A2. The C>T substitution converts Pro22Leu in the transporter's N-terminal cytoplasmic domain — a region that influences membrane trafficking and transporter turnover. Because SLC28A2 is on the plus strand, the plus-strand alleles match the coding strand directly: C is the reference, T is the Pro22Leu variant.

Ribavirin is a structural analog of guanosine that enters cells via CNT2 in the small intestine. Once inside enterocytes and erythrocytes, it is phosphorylated to ribavirin triphosphate, which cannot exit the cell easily. Red blood cells have no de-phosphorylation capacity, so ribavirin accumulates and disrupts membrane integrity — the direct cause of hemolytic anemia. The Pro22Leu variant appears to enhance CNT2 activity or increase transporter surface expression, leading to greater ribavirin uptake per unit of drug ingested.

Beyond ribavirin, CNT2 is the primary intestinal transporter for dietary and salvage-pathway purine nucleosides (adenosine, inosine, guanosine). Variants in this transporter may subtly shift purine nucleoside bioavailability and the balance between de-novo synthesis and the salvage pathway, though the clinical implications outside of drug therapy are not yet well characterised.

The Evidence

The clearest clinical evidence comes from a prospective cohort study of 216 Swiss HCV patients²² prospective cohort study of 216 Swiss HCV patients
Rau et al. J Hepatol 2013 treated with pegylated interferon-α plus ribavirin (with a subset receiving triple therapy including telaprevir or boceprevir). The TT genotype was associated with significantly higher weight-adjusted ribavirin serum levels at week 4 (p=0.02). Most strikingly, clinically significant anemia (haemoglobin drop requiring dose reduction) occurred in 56% of TT carriers versus only 33% of CC/CT carriers (p=0.006). In multivariate analysis, rs11854484 TT was an independent predictor of clinically significant anemia. Patients receiving triple therapy with protease inhibitors showed the same pattern, with TT genotype identifying a subgroup at substantially higher anaemia risk.

A pharmacokinetics study of 174 HCV-1 and HCV-4 Italian patients³³ pharmacokinetics study of 174 HCV-1 and HCV-4 Italian patients
D'Avolio et al. Ther Drug Monit 2012 identified rs11854484 TT genotype as one of three independent predictors of sustained virological response (alongside IL28B rs8099917 and CYP27B1 rs4646536), with the number of "favourable" variant alleles correlating inversely with treatment failure — suggesting that higher ribavirin exposure in TT carriers improves antiviral efficacy while simultaneously raising the risk of anaemia.

A secondary analysis of 169 HCV-1 patients treated with standard peg-IFN/ribavirin⁴⁴ secondary analysis of 169 HCV-1 patients treated with standard peg-IFN/ribavirin
Doehring et al. Pharmacogenet Genomics 2011 examined the full nucleoside transporter gene family (SLC28A2, SLC28A3, SLC29A1, SLC29A2) for ribavirin response; SLC28A2 variants (including rs11854484) modulated both ribavirin levels and haemoglobin outcomes.

Practical Actions

For TT homozygotes the key implication is raised awareness before any ribavirin-based treatment. Modern hepatitis C treatment is largely interferon-free and often ribavirin- free, but ribavirin is still used in some DAA (direct-acting antiviral) regimens for genotype 3 or retreatment cases. Knowing the TT genotype in advance allows clinicians to start at lower ribavirin doses, monitor haemoglobin more frequently (weekly for the first 4 weeks rather than every 2 weeks), and prepare for dose adjustment earlier — which preserves treatment completion rather than forcing discontinuation.

CT heterozygotes have intermediate ribavirin exposure and a modest elevation in anemia risk. Standard monitoring applies, but the genotype can inform shared decision-making with the treating hepatologist.

CC homozygotes have the reference transporter activity and the lowest anemia risk from this locus. Ribavirin dosing and monitoring follow standard protocols.

Interactions

rs11854484 (SLC28A2) operates within a genetic risk matrix for ribavirin-induced anaemia. The most important interaction partner is ITPA rs1127354, which encodes inosine triphosphatase — the enzyme that metabolises ribavirin triphosphate in erythrocytes. ITPA-deficient patients (rs1127354 CC) accumulate less ribavirin phosphate in RBCs and are paradoxically protected from haemolysis; the protective ITPA genotype partially counteracts the elevated ribavirin load in TT carriers (rs11854484). SLC28A3 rs56350726 and rs10868138 encode the related CNT3 transporter and have been associated with sustained virological response in some cohorts. An interaction between SLC28A2 TT and SLC28A3 variants would represent compounded transporter effects on ribavirin bioavailability.