Multiple sclerosis and the HLA-D region: linkage and association studies

Inheritance patterns of multiple sclerosis (MS) in multiplex families suggest a complex aetiology involving environmental and genetically determined components. The association between the HLA class II DR15, DQ6, Dw2 haplotype and MS has been well documented in patients with ancestral origins in Northern Europe. Conversely, linkage analysis of this region in multiplex families, derived from a population base, has generated negative results. Thus, given the Dw2 specificity association, evidence implicating this locus in disease susceptibility appears contradictory. We have collected and determined the HLA-DR and -DQ haplotypes of 115 sibling pairs with multiple sclerosis, and confirm a significant association with the Dw2-associated haplotype, both in index cases and their affected siblings compared with controls. However, using a sibling pair linkage analysis that restricts haplotype sharing probabilities to defined genetic models, we have not observed linkage of this region to susceptibility in MS. We discuss the basis for association and linkage and conclude that the DR15, DQ6, Dw2 haplotype does represent a susceptibility locus but its contribution to the pathogenesis is small; although it may interact epistatically with other susceptibility genes, this haplotype is not necessary for disease expression.     

Epidemiology and natural history of multiple sclerosis: new insights

PURPOSE OF REVIEW: The cause of multiple sclerosis remains elusive. We review recent epidemiological studies of genetic and environmental factors that influence susceptibility to the disease and its clinical course. RECENT FINDINGS: Genetic advances strengthen the association of multiple sclerosis with the human leukocyte antigen (HLA)-DRB1 allele and interferon-gamma polymorphisms and suggest that apolipoprotein E alleles play an important role. In the environmental realm, nested case-control studies show that prior Epstein-Barr virus exposure is overrepresented in multiple sclerosis. Smoking has been associated with both risk of multiple sclerosis and progressive disease. Vitamin D deficiency might tie together environmental clues with higher multiple sclerosis prevalence rates; dietary vitamin supplementation is also associated with reduced multiple sclerosis risk. Natural history studies demonstrated dissociation between relapses and disease progression, facilitated the ability to distinguish neuromyelitis optica and related syndromes from typical multiple sclerosis, and spawned the exploration of large datasets to model long-term disease activity. SUMMARY: Our understanding of the contributions of specific genetic and environmental factors that contribute to multiple sclerosis has improved. Further refinements will eventually allow powerful longitudinal studies to assess genetic and environmental interactions with implications for prediction of individual disease susceptibility, clinical course, and response to therapy.     

HLA‐DRB1: genetic susceptibility and disability progression in a Spanish multiple sclerosis population

Background and objective: The association of HLA‐DRB1*15 with susceptibility to multiple sclerosis (MS) has been consistently reported although its effect on the clinical phenotype is still controversial. The objectives of this study are to investigate the influence of the HLA‐DRB1 alleles on the genetic susceptibility to MS and to study their impact on disability progression in a Spanish population. Methods: HLA‐DRB1 typing was performed by PCR‐SSP in 380 patients with sporadic MS and 1088 unrelated healthy controls. Allelic frequencies were compared between groups. We studied the correlation between the different alleles and the progression of MS. Results: The HLA‐DRB1*15 allele in patients with MS had a statistically significant higher frequency when compared with controls (18.9% in patients vs. 10.1% in controls, Odds ratio (OR) = 2.07, 95% CI = 1.64–2.60, P < 0.001). In the univariate analysis, the DRB1*01 and DRB1*04 alleles were associated with a worse prognosis when considering the time to reach an EDSS of 6, whereas the DRB1*03 was correlated with a better outcome. In the multivariate analysis, the alleles*01 and *04 were demonstrated to be independent factors to have a worse prognosis. Conclusions: HLA‐DRB1*15 is associated with MS when comparing patients with unrelated healthy controls in a Spanish population. The HLA‐DRB1*01 and HLA‐DRB1*04 alleles are related to a worse prognosis when considering the time taken to reach severe disability.     

Association of HLA‐DRB1*15 allele and CSF oligoclonal bands in a Spanish multiple sclerosis cohort

Background and objective: The HLA‐DRB1*15 allele is consistently associated with multiple sclerosis (MS) susceptibility in most studied populations. This study investigated the association between HLA‐DRB1 alleles and the presence of oligoclonal immunoglobulin G bands (OCB) in the cerebrospinal fluid (CSF) in a Spanish population with MS. Methods: The HLA‐DRB1 typing was performed in 268 patients with sporadic MS and the detection of OCB in CSF. HLA‐DRB1 allelic frequencies were compared between OCB‐positive and OCB‐negative patients, and both groups were also compared with 1088 unrelated healthy controls. Moreover, we correlated the various HLA‐DRB1 genotypes, considering all the combinations of both parental alleles found with the presence or absence of OCB. Results: We found 206 OCB‐positive and 62 OCB‐negative patients. The HLA‐DRB1*15 allele in OCB‐positive patients had a higher frequency when compared with OCB‐negative patients (39.3% in OCB‐positive vs. 16.1% in OCB‐negative, OR = 1.38 95% CI = 1.18–1.61, P < 0.001). The other alleles did not show differences. When we compared with controls, the HLA‐DRB1*15 allele was associated with the disease only in the OCB‐positive patients group. None of the 55 genotypes found showed any association with the presence or absence of OCB. Conclusions: HLA‐DRB1*15 allele is associated with OCB‐positive patients with MS when studying a Spanish MS population.     

Influence of HLA on progression of optic neuritis to multiple sclerosis: results of a four-year follow-up study

BACKGROUND: Genetic predisposition in multiple sclerosis (MS) has always been a critical concern in aetiology and progress of the disease. The present study looks into the relations between human leukocyte antigen (HLA), optic neuritis (ON) and MS in the Iranian population. METHODS: Patients with potential diagnosis of acute ON underwent a standardized clinical examination for confirming the diagnosis. Selected patients were gathered for HLA typing and clinical follow up. RESULTS: Of the 55 patients, 46 (83.6%) were female. The mean age was 25(+/-7.3) with a range of 12-43. Twenty of the 55 (36%) were confirmed for the diagnosis of clinically definite MS (CDMS). Results show that A23, B21, A11 and B51 alleles were present in 4 (20%), 6 (30%), 2 (10%) and 1 (5%) of the CDMS patients, respectively. Ten (50%) and 17 (85%) CDMS patients were positive for HLA class II alleles, DR2 and DQ1, correspondingly. CONCLUSIONS: The study strongly suggests the association among DR2, A23 and B21 allele and the evolution of ON to MS. High prevalence of A23 and DR2 alleles in CDMS patients compared with the normal population may suggest an important role for these alleles in the development of MS. The study suggests B51 as a protective factor against development of ON in the normal population. In addition, results do not confirm previous studies considering A11 as a predisposing factor. The present study finally evokes that different classes of HLA have different roles in susceptibility to MS and confirms disease heterogeneity as an important emerging concept in MS.     

Correlations between Epstein-Barr virus antibody levels and risk factors for multiple sclerosis in healthy individuals

BACKGROUND: Female gender, human leukocyte antigen (HLA) DR2, tobacco smoking and Epstein-Barr virus (EBV) are established risk factors for multiple sclerosis (MS). Their possible interaction however, has been sparsely studied. OBJECTIVES: To investigate possible associations between EBV antibody levels and a range of other recognized MS risk factors. DESIGN, SETTING AND STUDY POPULATION: Cross-sectional study undertaken in Denmark based on 517 healthy individuals selected from the Danish population. METHODS: We measured change in mean log (anti-Epstein-Barr viral capsid antigen (VCA) immune globulin G) using linear regression. RESULTS: Anti-Epstein-Barr VCA immune globulin G levels were positively correlated with female gender and HLA DR2. Furthermore, current smoking and cumulative tobacco consumption were positively associated with EBV antibody levels. CONCLUSION: The association between Epstein-Barr VCA antibody levels and non-viral MS risk factors support the view that EBV is critically involved in the etiology of MS. These non-viral MS risk factors may be linked with MS risk through EBV-specific immune responses.     

人类白细胞抗原DRB1基因与多发性硬化遗传易患性研究

目的　分析多发性硬化遗传易患的分子免疫遗传背景。方法　采用聚合酶链反应序列特异性引物（ＰＣＲＳＳＰ） 联合技术对４５ 例病例组和１０５ 例正常对照组人类白细胞抗原ＤＲＢ１ 基因（ＨＬＡＤＲＢ１） 进行基因分型。结果　病例组ＨＬＡＤＲ２ 基因频率高于正常对照组，优势比为３．３２１ ，有统计学意义（ Ｐ＜ ０．０１）。结论　ＨＬＡＤＲ２ 基因与多发性硬化遗传易患相关联，提示可能还存在保护性基因。     

HLA-DRB1基因型与北方汉族多发性硬化易感性的研究

目的 探讨人类白细胞抗原(HLA)-DRB1基因型与中国北方汉族多发性硬化(MS)的关联.方法 应用序列特异性引物-聚合酶链反应(PCR-SSP)技术检测58例中国北方汉族MS患者及63名健康对照者的HLA-DRB1基因型分布;同时将MS患者分为西方型MS和视神经脊髓炎(NMO)两亚组,对其DR4和DR15基因频率进行比较.结果 与对照组比较,MS患者DR15和DR4等位基因频率显著升高(分别为P=0.025,P=0.003);此外,NMO亚组DR4频率显著高于西方型MS(P=0.013).结论 我国北方汉族人MS与HLA-DRB1等位基因的关联与西方人群有所不同,DR15可能是MS的易感基因,而DR4则可能为我国汉族人NMO的易感基因.关联基因的差异可能是导致东西方MS病变部位不同的原因.     

HLA-DRB1 and multiple sclerosis in Argentina

Background:  The association of multiple sclerosis (MS) with HLA DR subtypes, and particularly human leukocyte antigen (HLA)-DRB1*15 has been a consistent finding across nearly all Caucasian MS populations. In South America, scarce data exist about this issue. As the complete characterization of the HLA association range around the world is important to understand the role of this locus in MS susceptibility, we analyzed the frequency of HLA-DRB1* allelic groups in an MS population in Argentina.
Methods:  HLA-DRB1 locus was genotyped using PCR and sequence-specific primer amplification in 61 MS patients born in Buenos Aires, Argentina and 1216 healthy controls. Allele frequencies were compared between groups.
Results:  The HLA-DRB1*15 allele frequency significantly differed between controls and patients (13.5% and 33.9% respectively, P  < 0.001, OR 2.51, 95% CI: 1.7–3.0). The other allele frequencies did not show significant differences between patients and controls.
Conclusions:  The present HLA class II population study is in accordance with other Caucasian MS surveys which have found that HLA-DRB1*15 allele is strongly associated with MS disease. In Argentina, this is the first study performed to analyze the association of HLA-DRB1*15 and MS susceptibility in a Caucasian population and therefore contributes with new data to the immunogenomic global MS map.     

Multiple sclerosis: the environment and causation

PURPOSE OF REVIEW: We review current thinking on the aetiology of multiple sclerosis, how genetic susceptibility interacts with environmental risk factors at the population level, multiple sclerosis-associated risk factors and contemporary causation theory. RECENT FINDINGS: Two large genomic studies have confirmed the unambiguous associations with the DRB1 and DQB alleles of the human leucocyte antigen class II region. No other region with genome-wide significance has been identified. Family-based genetic epidemiological approaches have found no evidence of nongenetic transmissibility. This indicates that the action of the environment in influencing multiple sclerosis risk is operative at a macroenvironmental or population level, and not within families or the microenvironment. Environmental factors receiving renewed attention include vitamin D status, Epstein-Barr virus infection and smoking. Bradford Hill's criteria for causation have been modified and should be adopted as a framework for demonstrating causation in relationship to multiple sclerosis. SUMMARY: Multiple sclerosis is a complex disease because of interaction between genes and the environment. Any theory of causation for a specific agent will have to be congruent with the biology of the disease.     

The association between cigarette smoking and multiple sclerosis

Genetic factors partially explain the susceptibility of multiple sclerosis (MS) and might even relate to the clinical course. Still, many epidemiological studies point at an important role for environmental factors in MS. Smoking is one of the major candidates. In this review we provide an overview of the epidemiological studies on cigarette smoking and the association on MS risk and MS clinical course. In addition, we discuss the possible biological pathways that may influence neurological damage in MS. Moreover, the relation of smoking with other environmental MS risk factors will be addressed.     

Multiple sclerosis complexity in selected populations: the challenge of Sardinia, insular Italy.

Several lines of evidence indicate a genetic contribution to multiple sclerosis (MS) both in terms of predisposition to the disease and of immunological mechanisms which are known to play crucial roles in MS pathogenesis. The presence of high- and low-risk areas for MS in neighbouring regions supports the theory that MS predisposition is influenced by a complex interaction of genetic and environmental factors. Therefore, the use of genetically homogeneous and geographically isolated populations becomes an increasing requirement to reduce biasing biological variables. Sardinians fulfil these conditions well because of their different phylogeny from Europeans and the unique selective pressures which shaped their genome. Sardinians display amongst the highest MS prevalence rates world-wide and increasing MS incidence rates over time. Also, MS in Sardinia is linked to distinct human leucocyte antigen (HLA) alleles and associated to different patterns of cytokine production from lymphoid cells of different HLA subtypes. In this context, recent findings and future perspectives on the peculiarities of Sardinian MS concerning genetic, immunological and epidemiological aspects are presented. So far, our results indicate that variations at the level of territorial distribution and HLA-association are present which render MS heterogeneous even in this ethnically homogeneous population.     

HLA-DR15 is associated with lower age at onset in multiple sclerosis

To date, more than a dozen studies have investigated the role of HLA genes in determining clinical course and disease severity in multiple sclerosis (MS); in each of these studies, however, patient sample size has been small, and no consistent pattern has emerged from the results. For the present study, we determined HLA class II genotypes and catalogued clinical and demographic data for a total of 948 patients, making our data set the largest ever used to investigate HLA genes in MS. Our goals were both to investigate the impact of HLA-DRB1 alleles on clinical course and disease severity in MS and to compare the frequencies of the established susceptibility allele DR15 in various clinicodemographic subgroups of MS patients. We found that, in addition to DR15, DR17 is positively associated with susceptibility to MS; that none of the HLA-DRB1 alleles influences course or outcome in MS; that carriers of DR15 are prone to MS development at an earlier age than noncarriers; and that differences in DR15 positivity rates, after stratification for diagnostic category and examination results, seem to reflect a gradient of phenocopy contamination, with rates increasing in proportion to the degree of clinical or paraclinical verification of the MS diagnosis.     

Ethnicity-dependent association of HLA DRB1-DQA1-DQB1 alleles in Brazilian multiple sclerosis patients

OBJECTIVE: The present study focused on human leukocyte antigen (HLA) DQB1, DQA1 and DRB1 allelic variation according to ethnicity and analyzed whether susceptibility to multiple sclerosis (MS) depends on population characteristics. METHODS: Eighty-eight healthy African-Brazilians and 92 healthy white Brazilians living in Rio de Janeiro City were selected and the HLA phenotype between the two ethnic groups was compared with 44 MS patients of African descent and 40 patients of European descent. HLA class II genes were performed using polymerase chain reaction (PCR) and PCR-sequence-specific primer amplification. RESULTS: DQA1*0201-0301 alleles were associated with the white Brazilian population (P < 0.001). The DRB*1501 allele was present in White Brazilians (P=0.003), and DRB1*03-1503 in African-Brazilians. The DRB1*1501 allele confers an ethnicity-dependent MS susceptibility in White patients and the DQB1*0602 allele confers genetic susceptibility regardless of ethnicity. CONCLUSION: Heterogeneous phenotypes occur in both Brazilian ethnic groups. Taking into account that the response to immunomodulator drugs for MS treatment changes according to the DRB1*1501 allele and African-American MS patients presented poor response to the interferons, phenotype heterogeneity of HLA loci found in this study could influence therapeutic decisions in the Brazilian MS population.     

Aboriginals with multiple sclerosis: HLA types and predominance of neuromyelitis optica

BACKGROUND: MS is common in people of northern European ethnicity who live in northern geographic areas; however, MS is rarely identified among aboriginal peoples living in the same areas. OBJECTIVES: To determine the prevalence, clinical features, HLA type, and viral infections associated with MS among aboriginals in Manitoba, Canada. METHODS: A retrospective study was performed in which the clinical features of all aboriginal patients with MS together with HLA type and human herpesvirus-6, HIV-1, human T-cell lymphotropic virus-1, and endogenous retrovirus associated with MS (MSRV) infections were analyzed and compared with results from nonaboriginal patients with MS. RESULTS: Seven aboriginals with MS were identified with a period prevalence among aboriginals of 40:100,000. Clinical features included relapsing-remitting (n = 6) or primary progressive (n = 1) phenotypes with aggressive disease courses and frequent involvement of optic nerves and spinal cord (n = 5) compared with nonaboriginal patients. Autopsy of one patient showed necrosis and eosinophil infiltrates in a cervical spinal cord lesion and a demyelinated optic nerve. Analysis of HLA alleles at the DRB1 and DQB1 loci indicated that the HLA types detected were common in aboriginals, but there were no HLA alleles previously associated with the development of MS. Analysis of the copy number of MSRV did not show differences among aboriginals and nonaboriginals with or without MS. CONCLUSIONS: Aboriginals of Algonkian background are at increased risk for an aggressive type of MS, resembling neuromyelitis optica, which is resistant to conventional MS treatments and occurs independently of HLA alleles previously associated with MS.     

HLA class II susceptibility to multiple sclerosis among Ashkenazi and non-Ashkenazi Jews.

OBJECTIVE: To look for HLA class II alleles and haplotypes conferring susceptibility to multiple sclerosis (MS) in the Jewish population of Israel. DESIGN: Population-based cohort of clinically definite patients with MS tested prospectively over 7 years. SETTING: Referral center in a neurology clinic at a university hospital in the greater Jerusalem area in Israel. PATIENTS: A total of 162 consecutive patients with clinically definite MS from the 2 main ethnic Jewish groups in Israel: 104 Ashkenazi (80 with a relapsing remitting or secondary progressive and 24 with a primary chronic progressive course of the disease) and 58 non-Ashkenazi (36 with a relapsing remitting or secondary progressive course and 22 with a primary chronic progressive course of the disease), matched with 132 Ashkenazi and 120 non-Ashkenazi healthy controls. MAIN OUTCOME MEASURES: The relationship between the various HLA class II alleles and haplotypes and MS, as defined by the polymerase chain reaction and sequence-specific oligonucleotide probe hybridization, among the Ashkenazi and the non-Ashkenazi Jewish sections and with respect to the different clinical courses of the disease. RESULTS: The haplotype DRB1*1501, DQA1*0102, DQB1*0602 was found to be associated with MS among both Ashkenazi and non-Ashkenazi patients (P<.001 and P =.04, respectively). Among the non-Ashkenazi patients, a new association of haplotypes DRB1*1303, DQA1*05, and DQB1*030 with MS was detected (P = .03). The MS susceptibility alleles, DRB 1* 1501, DQA1*0102, and DQB1*0602 , were found in association with the Ashkenazi patients (P<.001, P=.02, and P=.01, respectively); DRB1*1501 and DRB1*1303 were more frequently observed among the non-Ashkenazi patients (P = .03, P = .04, respectively). On subdivision of the patients into clinical subgroups, associations of DRB1*0801, DQA1*0102, DQA1*0401, and DQB1*0602 with primary chronic progressive MS among the Ashkenazi patients were evident (P = .03, P = .04, P = .04 and P = .05, respectively), whereas DRB1* 1501, DRB1*03011, and DQB1*0602 were associated with relapsing remitting or secondary progressive among the non-Ashkenazi patients (P = .05, P = .05, and P = .03, respectively). CONCLUSIONS: This study, unlike previous ones, is the first to show a significant association between HLA class II alleles and MS in the Jewish population. The association with the HLA-DR2-related haplotype is similar to that among non-Jewish white patients with MS. Moreover, our data support the possibility that DRB1*1501 is the susceptibility allele responsible for the association between this haplotype and MS in the Jewish population. Our study also underscores differences in HLA profiles between Ashkenazi and non-Ashkenazi patients, and between the different clinical courses of the disease. The latter may indicate that the clinical courses of MS are influenced by the genetic background.     

HLA antigens-linked genetic control in multiple sclerosis patients resistant and susceptible to infection

Patients with multiple sclerosis (MS) from the two Montreal MS clinics, were divided into two groups: one group of 61 patients (MS type I) who had no clinical history of susceptibility to recurrent respiratory tract infections and a second group of 58 patients (MS type II) who had persistent susceptibility to such infections since childhood. All patients were typed for the HLA tissue antigens. The HLA antigen frequencies of the total MS patient population, and of MS type I and MS type II patients were compared to those of a normal control population and each other. The HLA-DR2 and B7 antigen frequencies were significantly increased compared to the normal controls for all MS patients. MS type I patients had an increased frequency for HLA-Bw42 and DRw8 antigens; the frequency of HLA-A29 was lower than in the controls and MS type II patients. MS type II patients had a significantly increased frequency for DR3 and some HLA-DR3-associated phenotypes (A1 + DR3; B8 + DR3; A1 + B8 + DR3) as compared to controls and MS type I patients. These results are consistent with the existence of genes linked to the HLA antigens, such as immune response genes, which control the resistance or susceptibility of the patients to infection, and suggest that these HLA antigens could be associated with a difference in the evolution of MS, as observed in the MS type I and II patients [21].     

Multiple Sclerosis in Latin Americans: Genetic Aspects

Latin Americans (LA) are a heterogeneous, multiethnic group of individuals who inhabit the continental countries in Latin America (LATAM), Caribbean islands and constitute the largest ethnic minority in the USA. Commonly used terminology and ethno racial classifications to define these groups may not be accurate. Risk for multiple sclerosis (MS) among LA is generally low to medium but frequencies are increasing in the American hemisphere. Genome-Wide Association Studies (GWAS) in LA show diverse variants and genetic proportions among Mestizos, the most representative ethnic population, who themselves are the product of centuries of interracial mixing between Native Americans (or Amerindians), White Caucasian Europeans, and Black Africans. Genetic distribution diversity appears to be related to migratory and historical and socio-political factors in LATAM. Epidemiologic studies show an extremely low prevalence of MS among non-mixed Amerindians; this has been attributed to protective ancestral Asian genetics and possibly, environmental factors. Mestizos and biracial LA of African ancestry have more susceptibility to MS apparently due to the historical introduction of the European HLA-DRB1*1501 gene. Contribution from HLA typing, GWAS, and ancestry informative markers (AIMs) has been determinant in the current LA genetic understanding but more regional studies are needed. The relationship between genetics and disease regional distribution is emphasized.     

Population frequency of HLA haplotypes contributes to the prevalence difference of multiple sclerosis in Ireland

BACKGROUND: A recent epidemiological study of multiple sclerosis in County Donegal in the northwest of Ireland and County Wexford in the southeast found a significant prevalence difference of 63.9/100,000 (95% CI 49.3-82.7/100,000) between the two regions (Z = 3.94, p 相似文献   

HLA determinants of susceptibility to multiple sclerosis in an Arabian Gulf population

BACKGROUND: An association between HLA antigens and susceptibility to multiple sclerosis (MS) has been established, especially in Caucasian populations. Such associations have not been as clearly defined in many Arab populations, where even the frequencies of specific HLA antigens remain unclear OBJECTIVE: The study was designed to (i) investigate the frequencies of HLA Class I and II antigens in Kuwaiti Arabs with MS, and; (ii) assess possible inter-relationships between HLA Class II antigens and such clinical phenotypic variables in MS as age at onset, gender, disease subtype and scale of disability. SUBJECTS AND METHODS: HLA Class I (A, B, C) and Class II (DR, DQ) antigens' tissue-typing was performed by the standard complement-dependent microlymphocytotoxicity technique in two groups of age- and sex-matched Kuwaiti subjects: (i) 67 patients with definite MS (48 relapsing remitting, 19 relapsing-progressive) and (ii) 145 unrelated healthy controls. The frequencies of specific HLA types were then compared between patients with controls, and in the former, related to specified clinical parameters. RESULTS: The frequencies for the Class I antigens: A9, A10, A19, A33, B5 and CW4 appeared higher with the presence of MS, although the numbers of positive subjects were rather low. For the Class II antigens, frequencies of DR4, DQ5, DQ6, DQ7 and DQ8 were increased while those for DR6 and DR1 were decreased in the patients with MS. HLA types DR15 and DR4 were present at higher frequencies in patients with a younger age at disease onset; DR15 also appeared more frequent in the female patients. CONCLUSION: There is a trend towards an association between HLA Class II antigens (DR4, DQ6, DQ7 and DQ8) and MS in Kuwaiti subjects. Additionally, it appeared that DR4 and DR15 were more frequent in females and those with an early onset of the disease. These patterns of HLA Class II determinants of susceptibility to MS differ from reports in some other populations, and may reflect the recognized variability in genetic influence on HLA and disease expression.