A new CX3 CR1 genotype with implications for HIV disease progression.

Abstract

Among host factors contributing to the high inter-patient variability in HIV-1 disease progression, polymorphisms in genes encoding chemokine receptors and chemokine ligands play a crucial role. Recently, a rapid progression to AIDS has been linked to a structural variant of the chemokine receptor CX3CR1 [1]. CX3CR1, whose natural ligand is the chemokine fractalkine, acts as an HIV-1 co-receptor under restricted conditions [2]. Faure et al. [1] described two single nucleotide polymorphisms (SNP) in the CX3CR1 gene, a G–A and a C–T mutation, resulting in valin to isoleucin and threonin to methionin changes at codons 249 (Val249Ile) and 280 (Thr280Met), respectively. Using a restriction fragment length polymorphism methodology, they studied the distribution of these two SNP in 565 HIV-positive caucasian patients. Of the nine possible genotypes, three have never been detected (249-G/G followed by 280-C/T, 249-G/G followed by 280-T/T and 249-A/G followed by 280-T/T). Furthermore, in 10 CX3CR1-Met280 heterozygotes, the chromosome bearing Met280 always bore an isoleucin at position 249. Consistent with their findings, the authors suggested that the C/T substitution at position 280 occurred only when there was an A at codon 249. They thus identified only three haplotypes of CX3CR1: Val249 Thr280, Ile249 Thr280 and Ile249 Met280. Survival analysis performed on HIV-1 seroconvertors showed faster progression to AIDS for CX3CR1-Met280 homozygotes compared with CX3CR1-Thr280 homozygotes and CX3CR1-Met280 heterozygotes. Moreover, no significant effect was observed for CX3CR1-Val249Ile. According to their findings on haplotype distribution, the authors concluded that only patients homozygous for CX3CR1-Ile249 Met280 would progress faster to AIDS. In contrast to their observation, we report the identification of a new haplotype variant of CX3CR1. Using a similar restriction fragment length polymorphism technique, we studied the distribution of Val249Ile and Thr280Met among 268 patients from the Luxembourg HIV cohort. The analysis was performed by polymerase chain reaction, using 5′–GAGGTCCTCCAGG AAATCTGGCCCGTG–3′ and 5′–AGACACAAGG CTTTGGGATTC–3′ as forward and reverse primers, respectively [1], followed by digestion of the amplification products with the restriction enzymes AclI for Val249Ile and HpyCH4III for Thr280Met (Westburg, Leusden, the Netherlands). Seven patients (2.6%) were homozygous for CX3CR1-Ile249 Met280. This prevalence, as with the other genotype frequencies found in our study (data not shown), was in agreement with the frequencies reported by Faure et al. [1]. Nevertheless, we found a 43-year-old man, a caucasian HIV-1-positive patient who presented a 249-G/A 280-T/T genotype. This observation was confirmed by sequencing the amplification product of the patient, using an ABI PRISM BigDye Terminator Cycle Sequencing Kit v2.0 (Applied Biosystems/PE Belgium, Lennik, Belgium) and the forward primer employed for the polymerase chain reaction analysis (Fig. 1). This unusual genotype permits the description of the new CX3CR1 haplotype, Val249 Met280.Fig. 1.: (a) Restriction fragment length polymorphism analysis of CX3CR1 polymerase chain reaction fragments on a 3% agarose gel: digestion occurs in the absence of mutation (MW, molecular weight; A, non-digested fragment; B, Val249Ile digested with AclI; C, absence of digestion at codon 280 with HpyCH4III). (b) CX3CR1 sequence analysis: the arrow indicates a heterozygous G–A mutation at codon 249. (c) CX3CR1 sequence analysis: the arrow indicates a homozygous C–T mutation at codon 280.In summary, we demonstrated the existence of a CX3CR1-Met280 homozygote HIV-1-positive patient bearing a CX3CR1 Val249 Met280 haplotype. Therefore, although no statistical conclusion can be drawn on the basis of this single report, our study challenges the exclusive relationship reported by Faure and colleagues [1] between CX3CR1-Ile249 Met280 homozygosity and a bad prognosis in HIV disease. François Roman Sabrina Deroo Nathalie Franck Catherine Burgy Jean Servais Jean-Claude Schmit