GSK3ß genetic variability in patients with Multiple Sclerosis.

Glycogen synthase kinase-3 beta (GSK3ß) is a ubiquitous kinase that is part of multiple signaling pathways. It has neurotrophic/neuroprotective effects by mediating the actions of neurotrophic molecules in the brain, thus providing neuroprotection through modulation of energy metabolism. Notably, it has been demonstrated that GSK3ß is involved in Wnt-beta-catenin signaling, which contributes to the inhibition of myelination and remyelination processes in mammals. Three-hundred nineteen patients with MS and 294 age-matched controls were genotyped by allelic discrimination for four common GSK3ß variants (rs2199503, rs9826659, rs334558 and rs6438552) tagging about 100% of GSK-3ß variability. A statistically significant increased frequency of the rs334558 GG genotype was observed in patients as compared with controls (25.4% versus 17.7%, P=0.02; OR:1.58, 95%CI: 1.07-2.34). Stratifying MS patients according to the disease subtype, a statistically significant difference of rs334558 GG frequency was found between Relapsing Remitting (RR), but not Primary Progressive or Secondary MS, and controls (27.0% versus 17.7%, P=0.01; OR: 1.72, 95%CI: 1.13-2.61). GSK3ß rs334558 is a susceptibility factor for MS. As it is located in the promoter region, a possible explanatory mechanism could be an influence of the variant on the gene transcription rate.

Is KIF24 a genetic risk factor for Frontotemporal Lobar Degeneration?

Linkage analysis identified a region on chromosome 9p associated with Frontotemporal Lobar Degeneration (FTLD). A detailed analysis of candidate genes lying in this region demonstrated an association with Ubiquitin Associated Protein (UBAP)1. The distribution of five Single Nucleotide Polymorphisms (SNPs) located in the chromosome 9 haplotype identified via linkage analysis, including UBAP1 rs7018487, UBAP2 rs1785506 and rs307658, and KIF24 rs17350674 and rs10814083, has been determined in a population of 284 patients diagnosed with FTLD, including 245 with behavioural variant Frontotemporal Dementia (bvFTD), 23 with Progressive Aphasia and 16 with Semantic Dementia, compared with 318 age-matched controls. A statistically significant increased frequency of the KIF24 rs17350674 AA genotype was observed in patients compared with controls (7.4 versus 2.5%; P=0.0068, OR: 3.63, CI: 1.58-8.35). Considering each syndrome separately, similar results where obtained in bvFTD versus controls (7.7 versus 2.5%, P=0.005, OR: 3.26, CI: 1.40-7.57). Stratifying for gender, a statistically significant increased genotypic frequency was observed in female patients as compared with female controls (8.9 versus 2.5%, P=0.008, OR: 3.85, CI: 1.36-10.93). In silico analysis predicted that the substitution from W to L caused by the rs17350674 affects protein function (P<0.05). The KIF24 rs17350674 polymorphism likely acts as a risk factor for sporadic FTLD, but a replication study would be needed to confirm these preliminary findings.

Loss of epidermal growth factor regulation by cobalamin in multiple sclerosis.

We investigated whether the physiological regulation of cerebrospinal fluid (CSF) levels of tumor necrosis factor (TNF)-alpha, epidermal growth factor (EGF), and nerve growth factor (NGF) by cobalamin (Cbl) that is observed in rat and human central nervous system (CNS) is retained in the CSF of patients with multiple sclerosis (MS). The study involved 158 MS patients grouped on the basis of the different clinical courses (relapsing-remitting (RR), secondary-progressive (SP), and primary-progressive (PP)), and 76 gender- and age-matched control patients with other non-inflammatory and non-neoplastic neurological diseases. The MS patients were therapy-free at the time of lumbar puncture. CSF Cbl and EGF were blindly measured by means of radioimmunoassays, and CSF TNF-alpha, and NGF by means of highly sensitive enzyme-linked immunosorbent assays. Serum EGF was also measured in 38 of the MS patients and 20 healthy controls. CSF Cbl levels were significantly higher (RR patients 27.9+/-9.7 pg/ml, p<0.0001 vs. C; SP patients 25.4+/-8 pg/ml, p<0.02 vs. C), and CSF TNF-alpha and EGF levels significantly lower in the patients with the RR (TNF-alpha 28.3+/-23.4 x 10(-3) pg/ml, p<0.0001 vs. C; EGF 129.9+/-44.8 pg/ml, p<0.02 vs. C) or SP (TNF-alpha 20.5+/-20.5 x 10(-3) pg/ml, p<0.001 vs. C; EGF 116.5+/-24.8 pg/ml, p<0.05 vs. C) clinical course than in controls (Cbl 21+/-4.6 pg/ml; TNF-alpha 75.6+/-34.7 x 10(-3) pg/ml; EGF 170.2+/-54.8 pg/ml). There were no differences in CSF NGF or serum EGF levels between any of the MS clinical courses and controls. Our results indicate that: (a) the positive Cbl-mediated regulation of myelino- and oligodendrocyte-trophic EGF is lost in the CSF of RR- or SP-MS patients; (b) the decrease in EGF levels in the CSF may be one factor impeding CNS remyelination in MS; and (c) the PP clinical course may have different pathogenetic mechanism(s) also on the basis of the molecules investigated in this study.

FUS/TLS genetic variability in sporadic frontotemporal lobar degeneration.

Two hundred and fifty one Italian patients with sporadic frontotemporal lobar degeneration (FTLD) and 259 age-matched controls were tested for association with the tagging single nucleotide polymorphisms (SNPs) rs741810 and rs1052352 in the fused in sarcoma/translated in liposarcoma gene (FUS/TLS). Only patients negative for GRN mutations were included. Considering each SNP alone, no differences in either allelic or genotypic frequencies between patients and controls were found (P > 0.05), even stratifying according to gender or the presence of concomitant motor neuron disease. Haplotype analysis failed to detect haplotypes associated with FTLD. According to these results, FUS/TLS is not a susceptibility factor for the development of sporadic FTLD.

GRN variability contributes to sporadic frontotemporal lobar degeneration.

Mutations in the progranulin gene (GRN) are responsible for familial FTLD with ubiquitin pathology (FTLD-U). However, there are controversial data regarding the contribution of GRN variability to sporadic FTLD. We carried out an association study in 265 patients, who did not carry a GRN causal mutation, and 375 age-matched controls. Four tagging Single Nucleotide Polymorphisms (SNPs) were chosen generate 80% power to detect an allelic association with P < or = 0.01. In addition, a known functional SNP (rs5848) was included. An increased frequency of the rs4792938 CC genotype in cases compared with controls was observed (17.4 versus 10.4%, P=0.01, OR: 1.81, 95%CI: 1.15-2.85). Stratifying for gender, no differences were observed for all polymorphisms. Haplotype analysis failed to detect haplotypes associated with the disease. Our findings indicate that the GRN rs4792938 CC genotype represents a susceptibility factor for the development of FTLD in individuals who do not carry GRN causal mutations. This SNP is likely located in a regulatory region, thus an effect on GRN mRNA levels may be of mechanistic importance.

Cerebrospinal fluid progranulin levels in patients with different multiple sclerosis subtypes.

Progranulin has recently attracted attention due to the discovery of mutations in its encoding gene (GRN) in several cases of frontotemporal lobar degeneration, but also for a possible role in inflammatory processes. In adult central nervous system, GRN mRNA is expressed in forebrain, olfactory bulbs and spinal cord. Progranulin cerebrospinal fluid (CSF) levels were evaluated in 55 patients with multiple sclerosis (MS) as well as in 35 subjects with non-inflammatory neurological diseases (NIND), 7 individuals with other inflammatory neurological disease (OIND) and 8 controls (CON), matched for ethnic background, gender and age. No statistically significant differences were found in patients compared with either NIND, OIND or CON (P>0.05), even stratifying according to disease subtype or gender. A positive correlation between progranulin CSF levels and age was observed in patients (rho=0.29, P=0.03). According to these data, progranulin does not likely play a major role in the pathogenesis of MS.

Candidate gene analysis of semaphorins in patients with Alzheimer's disease.

Semaphorins of the SemaIV family are expressed in neurons and decreased in brains from patients with Alzheimer's disease (AD). Accumulation of an internalized form of Sema3A is associated with degeneration of neurons, making these molecules candidates for the development of AD. Single nucleotide polymorphisms (SNPs) rs36026860 and rs28469467 in Sema3A as well as rs13284404 and rs11526468 in Sema4D were analyzed in a population of 240 patients with AD compared with 222 age-matched controls. None of SNPs in Sema3A were present, either in patients or controls. The distribution of the Sema4D rs11526468 and rs13284404 SNPs was not significantly different between patients and controls, even stratifying for gender or age at onset. In silico analysis predicted that rs11526468 and rs28469467 are probably damaging. This high degree of conservation of Sema3A suggests a very important role for this protein. However, neither Sema3A nor Sema4D likely influence the susceptibility to AD.

Rs5848 variant influences GRN mRNA levels in brain and peripheral mononuclear cells in patients with Alzheimer's disease.

Mutations in the progranulin gene (GRN), causative for Frontotemporal Lobar Degeneration with ubiquitin-immunoreactive neuronal inclusions (FTLD-U), could also be associated with Alzheimer's disease (AD). The influence of GRN genetic variability on susceptibility to AD and on expression levels in a series of neuropathologically-confirmed AD patients as well as in peripheral mononuclear cells (PBMC) and in cells isolated from cerebrospinal fluid (CSF) was investigated. An association study of rs9897526 and rs5848 was carried out in an Italian population and in a replication population of European American patients and controls. None of the variants tested act as unequivocal susceptibility factor in both populations although rs9897526 anticipated the onset of the disease in the Italian population. GRN expression in the parietal lobe of AD cases showed a 0.76-fold decrease compared with controls (1.31 +/- 0.07 versus 1.73 +/- 0.12, P = 0.0025). Patients carrying the rs5848 TT genotype had the lowest GRN expression levels (0.96 +/- 0.12, P = 0.014). Despite no significant differences were found in the relative PBMC and CSF GRN expression in patients compared to controls, stratifying patients according to the presence of rs5848 T allele, a 0.57-fold decrease in GRN mRNA levels over C carriers was found in PBMC (1.22 +/- 0.23 versus 0.70 +/- 0.12, P = 0.04). Similarly to data obtained in brain samples, patients carrying the TT genotype showed the lowest GRN mRNA levels (TT = 0.46 +/- 0.14, CC = 1.22 +/- 0.23; P = 0.013). These data argue against a direct role of GRN as a susceptibility factor for sporadic AD but support a role of GRN as a disease-modifying gene, possibly contributing to the failure of neuronal survival.

MCP-1 A-2518G polymorphism: effect on susceptibility for frontotemporal lobar degeneration and on cerebrospinal fluid MCP-1 levels.

The distribution of the MCP-1 A-2518G single nucleotide polymorphisms (SNP) was analyzed in a population of 212 patients with frontotemporal lobar degeneration (FTLD) compared with 203 age-matched controls. A significantly decreased allelic frequency of the G allele in patients compared with controls was observed (21.1 versus 29.3%, P = 0.011, OR: 0.59, CI: 0.40-0.87). Stratifying according to gender, the association was maintained in male patients versus male controls (17.8 versus 29.4%, P = 0.016, OR = 0.46, 95% CI: 0.25-0.84), but not in female patients compared with female controls (23.5 versus 29.2%, P > 0.05). The frequency of apolipoprotein E epsilon4 carriers was increased in patients (26.4 versus 13.8%, P = 0.0015, OR: 2.24, 95% CI: 1.37-3.67). Apolipoprotein E status did not influence the distribution of the A-2518G SNP. Monocyte chemotactic protein (MCP)-1 levels were determined in cerebrospinal fluid (CSF) collected from 23 patients and 17 controls. MCP-1 CSF levels were increased in patients compared with controls (449.01 +/- 27.57 versus 364.19 +/- 23.75 pg/ml, P = 0.011). Stratifying patients according to the presence of the polymorphic allele, significantly increased CSF MCP-1 levels were observed in carriers of the G allele compared with non-carriers (502.21 +/- 44.57 versus 395.87 +/- 21.92 pg/ml, P = 0.045). The MCP-1 A-2518G SNP acts as protective factor for sporadic FTLD, possibly by influencing MCP-1 production.

CCL8/MCP-2 association analysis in patients with Alzheimer's disease and frontotemporal lobar degeneration.

CCL2/Monocyte Chemoattractant Protein (MCP)-1 and other chemokines sharing a similar sequence, including CCL8/MCP-2, are involved in neurodegeneration. A few Single Nucleotide Polymorphisms (SNPs) have been reported in CCL8/MCP-2, all of which are located in the same linkage block. One of them (rs1163763) leads to an aminoacidic substitution, implying a potential impact on the function of the protein. rs1133763 was tested for association in 219 patients with Alzheimer's disease (AD) and 209 with Frontotemporal Lobar Degeneration (FTLD) as compared with 231 age-matched controls. The distribution of CCL8/MCP-2 rs1133763 was not significantly different among patients with AD or FTLD and controls, even stratifying according to gender. CCL8/MCP rs1133763 SNP, or other variants in linkage disequilibrium with this variant, likely do not influence the susceptibility to AD or FTLD in Caucasians.

Candidate gene analysis of selectin cluster in patients with multiple sclerosis.

Three single nucleotide polymorphisms (SNPs) with a potential impact on the function of selectins (rs6133, rs4987310 and rs5368 substitutions localized in the coding regions of P-sel, L-sel and E-sel, respectively) were analyzed in an Italian population of 165 patients with multiple sclerosis (MS) as compared with 149 controls and in a replication American population of Caucasian descent consisting of 122 patients and 50 controls. No significant differences in either allelic or genotypic frequency in all the SNPs tested were found in the Italian population. A tendency to an increased frequency of the rs6133 T allele was observed in the American population, but applying the Bonferroni correction the significance threshold was not reached. Haploview analysis demonstrated that rs4987310 and rs5368 markers are in strong LD (D' = 0.97) in both populations. Combining the two SNPs, we found no difference in haplotype distribution in patients compared with controls, either in Italian or in American population. Despite the fact that selectins play a role in the pathogenesis of MS and their encoding genes are located in regions associated with the disease, the selectin gene cluster studied likely does not influence the susceptibility to MS in Caucasians.

Intrathecal levels of IL-6, IL-11 and LIF in Alzheimer's disease and frontotemporal lobar degeneration.

Cerebrospinal fluid (CSF) levels of interleukin (IL)-6, IL-11 and leukaemia inhibitory factor (LIF) were evaluated in 43 patients with Alzheimer's disease (AD) and 24 patients with frontotemporal lobar degeneration (FTLD) as compared with 30 agematched controls (CON), and correlated with clinical and demographic data and with CSF biomarkers amyloid beta (A beta)42, total tau and tau phosphorylated at position 181 (P-tau). CSF IL-11 mean levels were significantly increased in AD and FTLD as compared with CON (6.5 +/- 4.6 and 6.6 +/- 5.1 versus 3.1 +/- 3.3 pg/ml, P = 0.009). IL-6 mean levels did not differ between patients and CON (P > 0.05),whereas LIF levels were not detectable in patients or in CON. In AD patients, a significantly positive correlation between MMSE scores and IL-11 CSF concentration was observed (r = 0.344, P = 0.028). No correlations with CSF A beta 42, total tau and P-tau were found. IL-11, but not IL-6 levels are increased in AD and FTLD, and the highest peaks were observed in patients with a less severe degree of cognitive deterioration, therefore suggesting a role of this cytokine in early phases of neurodegeneration.

Gender-specific influence of the chromosome 16 chemokine gene cluster on the susceptibility to Multiple Sclerosis.

Macrophage-derived chemokine (MDC/CCL22) plays a role in Experimental Autoimmune Encephalomyelitis (EAE), the animal model of Multiple Sclerosis (MS). MDC/CCL22 gene is part of a chemokine cluster, which includes also thymus and Activation-Regulated Chemokine (TARC/CCL17). The frequency of the C/T and C/A Single Nucleotide Polymorphisms (SNPs) in the promoter and coding sequence of CCL22 as well as the C/T SNP in the promoter of CCL17 were determined in 370 patients with Multiple Sclerosis (MS) compared with 380 controls. A trend towards a decreased allelic frequency of the A allele of the CCL22 C/A SNP as well as of the T allele of the CCL17 C/T SNP was found in patients compared with controls. The frequency of the AT haplotype was significantly decreased in MS patients (P=0.017, OR: 0.49, CI: 0.28-0.87). Stratifying patients according to gender, the observed association was even more pronounced in male patients compared with male controls (P=0.004, OR=0.18, 95% CI: 0.06-0.50), whereas no significant differences were observed in females. Therefore, the presence of the AT haplotype in chromosome 16 chemokine cluster is likely to confer a decreased risk of developing MS, particularly in males.

Association of a NOS1 promoter repeat with Alzheimer's disease.

The gene encoding NOS-I (NOS1) displays a complex transcriptional regulation, with nine alternative first exons. Exon 1c and 1f are the most abundant forms in the brain. A functional single nucleotide polymorphism (SNP) in exon 1c and a polymorphism in exon 1f, consisting of a variable number of tandem repeats (VNTR) originating short (S) and long (L) alleles, were studied in 184 patients with Alzheimer's disease (AD) and 144 gender- and age-matched controls. No differences were found for the Ex1c G-84A. The Ex1f-VNTR S allele was significantly more common in AD (55% versus 44%, P=0.009, OR=1.52) as was the S/S genotype (28% versus 14%, P=0.008; OR=2.37). The S allele showed a highly significant interaction with the ApoE epsilon 4 allele (OR: 10.83). Therefore, short alleles of the NOS1 exon 1f-VNTR are likely to be susceptibility factors for AD, and interact with the epsilon 4 allele to markedly increase the AD risk.

Candidate gene analysis of SPARCL1 gene in patients with multiple sclerosis.

Recently, proteomic analysis in cerebrospinal fluid (CSF) from patients with MS identified four proteins which are present in MS but not in normal human CSF, including SPARCL1, an extracellular matrix-associated protein member of the SPARC family. One hundred eighty-six patients with MS and 185 age-matched controls were genotyped for A/G single nucleotide polymorphism (SNP) in exon 1 (rs1049539), C/G SNP in exon 4 (rs1049544), resulting in a substitution of an aspartate with an histidine, and A/G substitution in the exon 5 (rs1130643), leading to the substitution of alanine with threonine. No significant differences in either allelic or genotypic frequency of the three SNPs were found (P>0.05), even in stratifying MS patients according to the course of the disease. Stratifying according to gender, a trend towards a decreased frequency of the C/C genotype of the rs1049544 was observed in male patients as compared with male controls (30.2% versus 44.0%; P=0.217). Despite proteomic studies in CSF from MS patients suggested an important role for SPARCL1 in the development of the disease, SPARCL1 gene does not appear to act as susceptibility factor for MS in the population investigated here. However, the frequency of the C/C genotype of rs1049544 was decreased in male patients, possibly conferring a lower risk of developing MS in male population. Further studies are needed to clarify this issue.

Absence of TREM2 polymorphisms in patients with Alzheimer's disease and Frontotemporal Lobar Degeneration.

Triggering Receptor Expressed on Myeloid cells (TREM)2 deficiency originates a genetic syndrome characterized by bone cysts and presenile dementia, named Nasu-Hakola disease (NHD). Early onset dementia and marked involvement of frontal regions are features characterizing both NHD and other kinds of neurodegenerative disorders, such as Frontotemporal Lobar Degeneration (FTLD), and, in some cases, Alzheimer's disease (AD). Three Single Nucleotide Polymorphisms (SNPs) in TREM2 coding region were screened by allelic discrimination in a population of probable AD patients as well as FTLD patients as compared with age-matched controls. In addition, mutation scanning of the coding region of TREM2 gene was carried out in 7 patients with early onset AD (EOAD), 16 FTLD, and 20 controls. None of the SNPs analyzed was present, either in patients or controls. Moreover, mutation scanning of the five exons of TREM2 failed to detect the presence of novel polymorphisms. These data demonstrate that TREM2 coding region is highly conserved, implying a crucial role of this receptor. Further studies, including a functional analysis, are certainly required to clarify the role of TREM2 in neurodegenerative processes.

Candidate gene analysis of IP-10 gene in patients with Alzheimer's disease.

Interferon-gamma-inducible Protein-10 (IP-10) is supposed to play a role in Alzheimer's disease (AD) development, as demonstrated by increased levels in cerebrospinal fluid from patients with AD. A mutation scanning of IP-10 exonic region was carried out in 10 patients with AD and 10 age-matched controls, demonstrating the presence of two previously reported single nucleotide polymorphisms (SNPs) in exon 4 (G-->C and T-->C) as well as a novel SNP in exon 2 (C-->T). Exon 4 G-->C and T-->C allelic variants were next evaluated in a population of 279 AD patients and 251 controls, in order to determine whether their presence could influence the susceptibility towards the development of the disease. These two SNPs were in complete linkage disequilibrium. No differences in haplotype frequencies were found in AD patients as compared with controls, even stratifying according to the presence of Apolipoprotein E varepsilon4 allele, gender or age at onset. A new protocol was developed to easily determine the C-->T SNP in exon 2. A preliminary analysis revealed a very low frequency of this allelic variant (1%). Therefore, the complete association study was not carried out because the size of our population was not sufficient to draw reliable conclusions. According to these results, IP-10 does not seem to be a risk factor for AD. However, a novel rare polymorphism has been identified, which could exert a role in AD susceptibility. Thus, further studies on larger populations are needed before confidently excluding IP-10 as a susceptibility gene for AD.

Serum MCP-1 levels are increased in mild cognitive impairment and mild Alzheimer's disease.

Upregulation of a number of chemokines, including monocyte chemotactic protein-1 (MCP-1), is associated with Alzheimer's disease (AD) pathological changes. Emerging evidence suggests that inflammatory events precede the clinical development of AD, as cytokine disregulation has been observed also in patients with mild cognitive impairment (MCI). MCP-1 levels were evaluated in serum samples from 48 subjects with MCI, 94 AD patients and 24 age-matched controls. Significantly increased MCP-1 levels were found in MCI and mild AD, but not in severe AD patients as compared with controls. mRNA levels in peripheral blood mononuclear cells (PBMC), evaluated by quantitative RT-PCR analysis, paralleled serum MCP-1 levels. Moreover, a progressive MCP-1 decrease was observed over a 1-year follow up in a subgroup of MCI subjects converted to AD. MCP-1 upregulation is likely to be a very early event in AD pathogenesis, by far preceding the clinical onset of the disease. Nevertheless, as MCP-1 is likely to play a role in several pathologies with an inflammatory component, a possible usefulness as an early AD biomarker would be possible only in combination with other molecules.

SELPLG and SELP single-nucleotide polymorphisms in multiple sclerosis.

P-Selectin (SELP) and P-selectin glycoprotein ligand-1 (SELPLG) constitute a receptor/ligand complex involved in the recruitment of activated lymphocytes, a critical event in the pathogenesis of multiple sclerosis (MS). In order to determine whether genetic variation in these pivotal molecules influences susceptibility to MS, we genotyped 214 Italian patients compared with 220 Italian controls for three single-nucleotide polymorphisms (SNPs): SELPLG Met62Ile, SELP C-2123G and SELP Thr715Pro. No significant differences in both SELP SNPs were found between patients and controls, whereas a decreased frequency of the Met62Ile SNP was found in patients versus controls in the Italian population (P = 0.025). To confirm these preliminary findings, the Met62Ile SNP was analysed in 938 UK trio families. This SNP did not show evidence for association with susceptibility to MS in the larger UK cohort. Therefore, none of the SNPs investigated is associated with MS, although this analysis does not conclusively exclude SELPLG and SELP as genetic risk factors for MS as much variation remains untested.

P-selectin glycoprotein ligand-1 variable number of tandem repeats (VNTR) polymorphism in patients with multiple sclerosis.

P-selectin glycoprotein ligand-1 (PSGL-1) is an important adhesion molecule involved in lymphocyte recruitment into the brain, which represents a crucial step in the pathogenesis of multiple sclerosis (MS). Three hundred twenty-one MS patients and 342 controls were genotyped for the presence of a polymorphism in the PSGL-1 gene, consisting of a variable number of tandem repeats (VNTR) originating three possible alleles: A, B and C, in order to test whether they influence the susceptibility and the course of the disease. No significant differences among allelic frequencies of A, B and C alleles in MS as compared with controls were observed. Stratifying patients according to the course of the disease, a significantly increased frequency of the shortest C allele in PP-MS was found (7.1%), either in comparison with controls (P=0.011) or with all other MS patients, who had acute inflammatory attacks at onset and an initial RR form (P=0.036). Besides, none of SP-MS patients was a carrier of the C allele and B carriers converted later from RR to SP course as compared with A/A subjects (after 15.8 rather than 8.8 years, P=0.01). In conclusion, the C allele of the VNTR polymorphism in PSGL-1 is likely to be associated with PP-MS. As this allele has been demonstrated to have a very low efficiency in mediating lymphocyte binding to brain endothelium during attacks, its high frequency in PP-MS could be related to the absence of exacerbations in such patients.