Showing papers by "Stephen J. O'Brien published in 2002"
TL;DR: The strongest synergistic effect of these loci was on progression to depletion of CD4+ T cells, which suggests that a protective response of NK cells involving KIR3DS1 and its HLA class I ligands begins soon after HIV-1 infection.
Abstract: Natural killer (NK) cells provide defense in the early stages of the innate immune response against viral infections by producing cytokines and causing cytotoxicity1. The killer immunoglobulin-like receptors (KIRs) on NK cells regulate the inhibition and activation of NK-cell responses through recognition of human leukocyte antigen (HLA) class I molecules on target cells2 KIR and HLA loci are both highly polymorphic, and some HLA class I products bind and trigger cell-surface receptors specified by KIR genes. Here we report that the activating KIR allele KIR3DS1, in combination with HLA-B alleles that encode molecules with isoleucine at position 80 (HLA-B Bw4-80Ile), is associated with delayed progression to AIDS in individuals infected with human immunodeficiency virus type 1 (HIV-1). In the absence of KIR3DS1, the HLA-B Bw4-80Ile allele was not associated with any of the AIDS outcomes measured. By contrast, in the absence of HLA-B Bw4-80Ile alleles, KIR3DS1 was significantly associated with more rapid progression to AIDS. These observations are strongly suggestive of a model involving an epistatic interaction between the two loci. The strongest synergistic effect of these loci was on progression to depletion of CD4+ T cells, which suggests that a protective response of NK cells involving KIR3DS1 and its HLA class I ligands begins soon after HIV-1 infection.
1,171 citations
TL;DR: This method has proven to be a reliable technique that can be incorporated into large‐scale surveys of Iberian lynx populations and exemplifies an approach that can easily be extended to other species.
Abstract: Noninvasive methods using genetic markers have been suggested as ways to overcome difficulties associated with documenting the presence of elusive species. We present and assess a novel, reliable and effective molecular genetic technique for the unequivocal genetic identification of faeces from the endangered Iberian lynx ( Lynx pardinus ). From mitochondrial DNA (mtDNA) cytochrome b and D -loop region sequences, we designed four species-specific primers (for products 130–161 bp long) that were considered to be likely to amplify degraded DNA. We compared two DNA extraction methods, various DNA amplification conditions and the robustness and specificity of the primer pairs with 87 lynx samples from 5 potentially different lynx populations and with 328 samples of other carnivore species. The utility of the identification technique was tested with faeces of different ages, with faeces from controlled field experiments, and with faeces collected from locales with possible lynx populations from throughout the state of Andalusia, Spain (8052 km 2 ). Faecal mtDNA extraction was more efficient using PBS wash of the faeces instead of a faeces homogenate. Our assay increased from 92.6 to 99% efficiency with a second amplification and a reduction in template concentration to overcome polymerase chain reaction (PCR) inhibition. Our assay never produced false positives, and correctly identified all lynx faeces. Of 252 faeces samples of unknown species collected throughout Andalusia, 26.6% (from three different areas) were classified as Iberian lynx, 1.4% showed evidence of PCR inhibition and 1.2% were of uncertain origin. This method has proven to be a reliable technique that can be incorporated into large-scale surveys of Iberian lynx populations and exemplifies an approach that can easily be extended to other species.
227 citations
TL;DR: The diminished transcription of RANTES afforded by the In1.1C regulatory allele is consistent with increased HIV-1 spread in vivo, leading to accelerated progression to AIDS.
Abstract: RANTES (regulated on activation normal T cell expressed and secreted), a ligand for the CC chemokine receptor 5, potently inhibits HIV-1 replication in vitro. We tested the influence of four RANTES single nucleotide polymorphism (SNP) variants and their haplotypes on HIV-1 infection and AIDS progression in five AIDS cohorts. Three SNPs in the RANTES gene region on chromosome 17 (403A in the promoter, In1.1C in the first intron, and 3′222C in the 3′ untranslated region) are associated with increased frequency of HIV-1 infection. The common In1.1C SNP allele is nested within an intronic regulatory sequence element that exhibits differential allele binding to nuclear proteins and a down-regulation of gene transcription. The In1.1C allele or haplotypes that include In1.1C display a strong dominant association with rapid progression to AIDS among HIV-1-infected individuals in African-American, European-American, and combined cohorts. The principal RANTES SNP genetic influence on AIDS progression derives from the down-regulating RANTES In1.1C allele, although linkage disequilibrium with adjoining RANTES SNPs including a weaker up-regulating RANTES promoter allele (−28G), can modify the observed epidemiological patterns. The In1.1C-bearing genotypes account for 37% of the attributable risk for rapid progression among African Americans and may also be an important influence on AIDS progression in Africa. The diminished transcription of RANTES afforded by the In1.1C regulatory allele is consistent with increased HIV-1 spread in vivo, leading to accelerated progression to AIDS.
197 citations
TL;DR: The association of HLA-Cw*04 with HCV persistence was codominant (two copies of the gene were more strongly associated with persistence than one copy) and these cells may be involved in recovery from HCV infection.
Abstract: In studies of acute hepatitis C virus (HCV) infection, the early host immune response is one of the determinants of viral persistence. The class I human leukocyte antigens (HLA), which present foreign antigen to cytolytic T cells, are integral components of this response. We hypothesized that the highly polymorphic HLA genes affect the outcome of an HCV infection. To test this hypothesis, we molecularly typed 231 persons with well-documented clearance of an HCV infection and 444 matched persistently infected persons. HLA-A*1101 (odds ratio [OR], 0.49; 95% confidence interval [95% CI], 0.27 to 0.89), HLA-B*57 (OR, 0.62; 95% CI, 0.39 to 1.00), and HLA-Cw*0102 (OR, 0.43; 95% CI, 0.21 to 0.89) were associated with viral clearance, whereas HLA-A*2301 (OR, 1.78; 95% CI, 1.01 to 3.11) and HLA-Cw*04 (OR, 1.78; 95% CI, 1.21 to 2.59) were associated with viral persistence. HLA-Cw*04 is in strong linkage disequilibrium with HLA-B*53 and HLA-B*35 , but only HLA-B*53 (OR, 1.70; 95% CI, 0.95 to 3.06) and the Cw*04-B*53 haplotype (OR, 1.76; 95% CI, 0.94 to 3.26) were weakly associated with viral persistence. HLA-B*53 has similar, but not necessarily identical, binding specificity to some HLA-B*35 subtypes ( B*35-Px group). The association with the B*35-Px group was less strong than with HLA-B*53 alone. The association of HLA-Cw*04 with HCV persistence was codominant (two copies of the gene were more strongly associated with persistence than one copy). However, HLA-Cw*04 was not associated with HCV RNA levels among the persistently infected individuals. Since Cw*04 is a ligand for the killer immunoglobulin-like receptors on natural killer cells, these cells may be involved in recovery from HCV infection. Further investigation is needed to understand the relationship between class I alleles and HCV clearance.
192 citations
TL;DR: The trans-rotator cuff technique is an effective and safe modality to address superior labral pathology and allows for a more optimal placement of a biodegradable fixation device and/or suture anchors into the superior labrum.
Abstract: Purpose: To discuss a new technique for the surgical treatment of type II SLAP lesions as well as the evaluation of the technique’s effectiveness with a minimum 2-year follow-up. Type of Study: Retrospective clinical follow-up study. Methods: We present a clinical follow-up of 31 patients who were treated arthroscopically for type II SLAP lesions using a trans-rotator cuff portal at an average follow-up time of 3.7 years. Patients were screened for concomitant procedures including rotator cuff repairs, shoulder stabilizations, thermal capsullographies, and previous surgeries. These patients were subsequently excluded from the study. Patients were given a standard physical examination of the upper extremity at our institution and they completed both the L’Isalata and American Shoulder and Elbow Surgeons questionnaires. Results: All 31 patients identified were available for follow-up at an average time of 3.7 years postoperatively (range, 2.0 to 7.4 years). The average L’Insalata score was 87.0 points (range, 46.1-100 points); the average ASES score was 87.2 points (range, 46.7-100 points). The average pain score was 1.5 (range, 0-5) and only 4 of the 31 patients complained of moderate pain with activity. Sixteen of the 31 patients returned to their preinjury level of sports; 11 of the 31 patients returned to limited activity and 2 patients were inactive at the time of follow-up. Overall satisfaction with the procedure averaged 3.79 points (range, 0-5 points): 22 patients rated overall satisfaction as good or excellent, 6 patients reported a fair outcome, and only 3 patients were unsatisfied with the results of the surgery. One patient who was unsatisfied with the procedure had reinjured his superior labrum and required a second operation. None of the 31 patients had symptoms suggestive of rotator cuff pathology. Of the 30 patients found to have a positive Active Compression test preoperatively, 26 of these patients now had a negative sign. Conclusions: The trans-rotator cuff approach allows for a more optimal placement of a biodegradable fixation device and/or suture anchors into the superior labrum. Furthermore, we believe that this approach does not compromise the function of the rotator cuff. The trans-rotator cuff technique is an effective and safe modality to address superior labral pathology. Key Words: Shoulder—Arthroscopy—SLAP—Labral repair— Trans-rotator cuff approach—Clinical follow-up.
161 citations
TL;DR: The savannah elephants show significantly lower genetic diversity than forest elephants, probably reflecting a founder effect in the recent history of the savannah species.
Abstract: The highly threatened African elephants have recently been subdivided into two species, Loxodonta africana (savannah or bush elephant) and L. cyclotis (forest elephant) based on morphological and molecular studies. A molecular genetic assessment of 16 microsatellite loci across 20 populations (189 individuals) affirms species level genetic differentiation and provides robust genotypic assessment of species affiliation. Savannah elephant populations show modest levels of phylogeographic subdivision based on composite microsatellite genotype, an indication of recent population isolation and restricted gene flow between locales. The savannah elephants show significantly lower genetic diversity than forest elephants, probably reflecting a founder effect in the recent history of the savannah species.
123 citations
TL;DR: Assessment of patterns of genomic diversity for ninety feline microsatellite loci among previously characterized populations of cheetahs, lions and pumas in recapitulating demographic history implies that the micros Satellite diversity measures offer proportionate indicators of historic population bottlenecks and founder effects.
Abstract: Nuclear microsatellite loci (2- to 5-bp tandem repeats) would seem to be ideal markers for population genetic monitoring because of their abundant polymorphism, wide dispersal in vertebrate genomes, near selective neutrality, and ease of assessment; however, questions about their mode of generation, mutation rates and ascertainment bias have limited interpretation considerably. We have assessed the patterns of genomic diversity for ninety feline microsatellite loci among previously characterized populations of cheetahs, lions and pumas in recapitulating demographic history. The results imply that the microsatellite diversity measures (heterozygosity, allele reconstitution and microsatellite allele variance) offer proportionate indicators, albeit with large variance, of historic population bottlenecks and founder effects. The observed rate of reconstruction of new alleles plus the growth in the breadth of microsatellite allele size (variance) was used here to develop genomic estimates of time intervals following historic founder events in cheetahs (12,000 yr ago), in North American pumas (10,000-17,000 yr ago), and in Asiatic lions of the Gir Forest (1000-4000 yr ago).
109 citations
TL;DR: The results further support the conclusion that Delta32-mediated resistance is incomplete and is associated with acquisition of exclusively-X4 variants of HIV-1.
Abstract: Homozygosity for the 32 base-pair deletion (Delta32/Delta32) in the CCR5 coreceptor gene is associated with incomplete HIV-1 resistance. Six HIV-1-infected Delta32/Delta32 patients have been reported. We report 2 additional Delta32/Delta32-infected individuals, among 106 seroconverters in a vaccine preparedness study. Like the previous 6, these individuals experienced rapid CD4 decline. However, taken together, the 8 patients have neither uniformly high virus load nor rapid progression to AIDS. We obtained five virus isolates from 1 patient at 5, 6, 7, 10, and 12 months after the estimated time of infection. The earliest isolate exhibits the syncytium-inducing (SI) phenotype and exclusive use of the CXCR4 coreceptor, suggesting acquisition of HIV-1 through this coreceptor. Of the remaining 104 seroconverters, 8 were CCR5-Delta32/+ and 96 were CCR5-+/+. Three CCR5-+/+ seroconverters who showed the uncommon pattern of early SI virus and rapid CD4 decline had uniformly high viral load and more heterogeneous coreceptor usage. These results further support the conclusion that Delta32-mediated resistance is incomplete and is associated with acquisition of exclusively-X4 variants of HIV-1. The pathogenic potential of these viruses may be different from late-stage X4 virus or early X4 virus acquired by individuals with other CCR5 genotypes.
98 citations
TL;DR: Thermal capsular shrinkage may be of limited value for patients who have had prior operations or have a history of multiple dislocations, and should be used cautiously in patients with multidirectional instability or in those who are involved in contact sports.
Abstract: Thermal capsular shrinkage has rapidly become a common procedure for a variety of shoulder conditions usually associated with instability, although clinical data on outcomes are limited. The objective of this study was to identify risk factors for poor outcome after thermal capsulorrhaphy. Of 106 patients who underwent thermal shrinkage, 15 patients with treatment failures were identified. The mean time to failure after the procedure was 6.3 months (range, 1 to 16). Previous operations and multiple recurrent dislocations were associated with poor outcome at a highly significant level. Multidirectional instability and participation in contact sports did not attain statistical significance as risk factors. However, statistical power in these two comparisons was insufficient to exclude them as potential risk factors. A concomitant procedure at the time of thermal capsulorrhaphy was not associated with poor outcome. The data from early treatment failures can be useful in guiding patient selection for thermal capsulorrhaphy. This procedure may be of limited value for patients who have had prior operations or have a history of multiple dislocations. The data also suggest that thermal capsulorrhaphy should be used cautiously in patients with multidirectional instability or in those who are involved in contact sports.
70 citations
TL;DR: The advantages, rationale, and present strategy of a feline genome project are reviewed, and the disease models, comparative genomics, and biological applications posed by the full resolution of the cat's genome are described.
Abstract: The compilation of a dense gene map and eventually a whole genome sequence (WGS) of the domestic cat holds considerable value for human genome annotation, for veterinary medicine, and for insight into the evolution of genome organization among mammals. Human association and veterinary studies of the cat, its domestic breeds, and its charismatic wild relatives of the family Felidae have rendered the species a powerful model for human hereditary diseases, for infectious disease agents, for adaptive evolutionary divergence, for conservation genetics, and for forensic applications. Here we review the advantages, rationale, and present strategy of a feline genome project, and we describe the disease models, comparative genomics, and biological applications posed by the full resolution of the cat's genome.
69 citations
TL;DR: A molecular genetic survey of nuclear microsatellite and mitochondrial DNA sequence variation validates subspecies distinctiveness but also reveals a markedly reduced level of genetic variation, which indicates a critically diminished wild population under severe threat of extinction.
Abstract: The Far Eastern or Amur leopard (Panthera pardus orientalis) survives today as a tiny relict population of 25-40 individuals in the Russian Far East. The population descends from a 19th-century northeastern Asian subspecies whose range extended over southeastern Russia, the Korean peninsula, and northeastern China. A molecular genetic survey of nuclear microsatellite and mitochondrial DNA (mtDNA) sequence variation validates subspecies distinctiveness but also reveals a markedly reduced level of genetic variation. The amount of genetic diversity measured is the lowest among leopard subspecies and is comparable to the genetically depleted Florida panther and Asiatic lion populations. When considered in the context of nonphysiological perils that threaten small populations (e.g., chance mortality, poaching, climatic extremes, and infectious disease), the genetic and demographic data indicate a critically diminished wild population under severe threat of extinction. An established captive population of P. p. orientalis displays much higher diversity than the wild population sample, but nearly all captive individuals are derived from a history of genetic admixture with the adjacent Chinese subspecies, P. p. japonensis. The conservation management implications of potential restoration/augmentation of the wild population with immigrants from the captive population are discussed.
TL;DR: The development of 18 polymorphic microsatellite markers for the endangered Spanish imperial eagle are described and revealed as good molecular tools for genetic population studies, individual identification and parentage assessment inSpanish imperial eagle and closely related species.
Abstract: Here we describe the development of 18 polymorphic microsatellite markers for the endangered Spanish imperial eagle ( Aquila adalberti ). Microsatellites were tested in five other raptor species. These markers were revealed as good molecular tools for genetic population studies, individual identification and parentage assessment in Spanish imperial eagle and closely related species.
TL;DR: The data are consistent with the hypothesis that higher levels of virus-specific CTL contribute to protection against HIV disease progression in infected individuals with B-35-PY, but not in those with B*35-px.
Abstract: Human immunodeficiency virus type 1 (HIV-1)-infected individuals with HLA-B*35 allelic variants B*3502/3503/3504/5301 (B*35-Px) progress more rapidly to AIDS than do those with B*3501 (B*35-PY). The mechanisms responsible for this phenomenon are not clear. To examine whether cellular immune responses may differ according to HLA-B*35 genotype, we quantified HIV-1-specific CD8+-T-cell (CTL) responses using an intracellular cytokine-staining assay with specimens from 32 HIV-1-positive individuals who have B*35 alleles. Among them, 75% had CTL responses to Pol, 69% had CTL responses to Gag, 50% had CTL responses to Nef, and 41% had CTL responses to Env. The overall magnitude of CTL responses did not differ between patients bearing B*35-Px genotypes and those bearing B*35-PY genotypes. A higher percentage of Gag-specific CTL was associated with lower HIV-1 RNA levels (P = 0.009) in individuals with B*35-PY. A negative association between CTL activity for each of the four HIV antigens and viral load was observed among individuals with B*35-PY, and the association reached significance for Gag. No significant relationship between CTL activity and viral load was observed in the B*35-Px group. The relationship between total CTL activity and HIV RNA among B*35-Px carriers differed significantly from that among B*35-PY carriers (P < 0.05). The data are consistent with the hypothesis that higher levels of virus-specific CTL contribute to protection against HIV disease progression in infected individuals with B*35-PY, but not in those with B*35-Px.
TL;DR: Negative prognostic factors evaluated are presence of glenohumeral arthritis, decreased passive range of motion, superior migration of the humeral head, presence of atrophy, and external rotation/abduction strength less than 3.2 years posttreatment.
Abstract: ObjectiveTo investigate the negative prognostic factors in the management of massive rotator cuff tears.DesignRetrospective nonrandomized study.SettingFaculty Practice associated with a major orthopedic teaching hospital.Patients108 patients who were treated for massive rotator cuff tears were evalu
01 Jan 2002
TL;DR: With over 65 million cats in the United States today (Pet Food Institute, Washington, D.C.), a large percentage of U.S. households have a cat and thus an abundance of cat hair, which could be used by a forensic laboratory to provide a link between the perpetrator of a crime and a crime scene.
Abstract: With over 65 million cats in the United States today (Pet Food Institute, Washington, D.C.), a large percentage of U.S. households have a cat and thus an abundance of cat hair. With the appropriate DNA tools, cat hairs could be used by a forensic laboratory to provide a link between the perpetrator of a crime and a crime scene. An assailant may unknowingly carry clinging cat hairs from a victim’s cat away from the scene of a crime, or hair from the perpetrator’s cat may be left at the scene (1). Either scenario may provide a crucial link and help solve an important case. In the most famous case to date, DNA analysis of hair from a cat named Snowball was used to link a murder suspect to a crime scene—a result that led to a criminal conviction (2).
TL;DR: With this technique, areas that are often difficult to expose in an open fashion and those previously deemed inaccessible arthroscopically are localized readily and thought should be given to the possibility ofArthroscopic retrieval or excision before proceeding with open surgery.
Abstract: Two cases of arthroscopic retrieval of intra-articular shoulder pathology are presented. With this technique, areas that are often difficult to expose in an open fashion and those previously deemed inaccessible arthroscopically are localized readily. In the setting of intra-articular pathology, thought should be given to the possibility of arthroscopic retrieval or excision before proceeding with open surgery.
TL;DR: Cats previously infected with LLV or PLV were able to more effectively control FIV infection and resist its immunologic effects, despite the substantial genetic divergence between these lentiviruses-raising the possibility that superinfection may impart resistance to lentivirus infection by heightening innate immune mechanisms.
Abstract: Lion lentivirus (LLV) and puma lentivirus (PLV) exist as highly divergent virus clades among populations of indigenously infected nondomestic felidae. The feline immunodeficiency virus (FIV) is highly divergent from LLV and PLV and is pathogenic for domestic cats. When domestic cats are infected with LLV or PLV, they have immunologically and clinically silent persistent infections. We examined whether LLV or PLV infection might impart resistance to FIV superinfection in vitro by infecting domestic cat lymphoid cells with PLV and assessing resistance of these cells to FIV. We found that infection with FIV was highly restricted by prior established PLV infection. To examine whether this resistance applied in vivo, domestic cats were asymptomatically infected with either LLV or PLV and then challenged with pathogenic FIV. Although all cats became infected with FIV, prior LLV or PLV exposure blunted CD4 + cell depletion and suppressed plasma and peripheral blood mononuclear cell FIV loads relative to FIV-challenged controls not infected with LLV or PLV, despite the lack of prechallenge neutralizing antibody activity against FIV. Thus, as compared with naive controls cats previously infected with LLV or PLV were able to more effectively control FIV infection and resist its immunologic effects, despite the substantial genetic divergence between these lentiviruses-raising the possibility that superinfection may impart resistance to lentivirus infection by heightening innate immune mechanisms.
Journal Article•
TL;DR: Observations demonstrate the direct mutagenic potential of the lentiviruses and identify a new candidate tumor suppressor gene.
Abstract: Infection with immunosuppressive lentiviruses is associated with increased cancer risk,but most studies have implicated indirect mechanisms as the tumor cells generally lack integrated viral sequences. An exception wasfound in a B-cell lymphoma (Q254) where the tumor cells contained a single integrated feline immunodeficiency virus genome. Additional analysis now indicates that feline immunodeficiency virus integration in lymphoma Q254 resulted in promoter insertion and truncation of a conserved gene on feline chromosome B3, whereas the unaffected allele of the gene appeared to be transcriptionally down-regulated. The orthologous human gene (FLJ12973), is expressed ubiquitously and encodes a WD-repeat protein with structural similarity to DDB2, the small subunit of the xeroderma pigmentosum XP-E complex. Moreover, the gene is located within a region of frequent tumor-specific deletions on chromosome 15q15. These observations demonstrate the direct mutagenic potential of the lentiviruses and identify a new candidate tumor suppressor gene.
TL;DR: In this paper, Copeland et al. take a look at the mysteries of mouse chromosome 16 and comment on the similarities and differences in the organization of the mouse and human genome.
Abstract: Excitement over the completed human genome sequence may have waned, but the mighty mouse is ready to take center stage. In a lively Perspective,
Copeland and colleagues
take a look at the mysteries of mouse chromosome 16 (
Mural
et al.) and comment on the similarities and differences in the organization of the mouse and human genome.
TL;DR: This technique employs the application of gentle leverage to pry apart the surfaces of the ulnohumeral articulation when viewing and working posteriorly to improve visualization and access to the ulngumeral and radiocapitellar articular spaces.
Abstract: Visualization and access are of fundamental importance in arthroscopy, including arthroscopy of the elbow. A new technique not previously described in the literature improves both of these factors for key areas within the elbow that would otherwise be inaccessible. This technique employs the application of gentle leverage to pry apart the surfaces of the ulnohumeral articulation when viewing and working posteriorly to improve visualization and access to the ulnohumeral and radiocapitellar articular spaces. We believe this technique is essential for full arthroscopic viewing of the intra-articular regions of the ulnohumeral and radiocapitellar joints.
01 Jan 2002
TL;DR: The identification of genetic factors that regulate HIV-1 infection and AIDS kinetics has clarified the view of viral pathogenesis by illuminating the importance of host-virus interactions at virtually every stage of infection.
Abstract: The identification of genetic factors that regulate HIV-1 infection and AIDS kinetics has clarified our view of viral pathogenesis by illuminating the importance of host-virus interactions at virtually every stage of infection. Genetic studies often point to unexpected roles for host factors, providing insights into immune regulation of HIV-1 replication and possible selective forces that may influence HIV-1 quasispecies evolution. Host genetic factors have been shown to affect susceptibility to infection, the rate of CD4 + T-cell depletion, and the rate of progression to AIDS. Thus, it is important to consider the genetic background of the host when assessing the efficacy of antiretroviral agents and vaccines in clinical trials.
TL;DR: This work describes an arthroscopic assisted rotator interval closure technique that, in the appropriately selected patient, is effective for treating particular shoulder instability.
Abstract: Arthroscopy has revolutionized the way shoulder surgeons have addressed intra-articular pathology. Continued advancements in technique and instrumentation have resulted in more and more procedures being performed on an all-arthroscopic basis. Appropriate caution has been taken with regard to applying arthroscopic techniques for all shoulder procedures, particularly instability. We describe an arthroscopic assisted rotator interval closure technique that, in the appropriately selected patient, is effective for treating particular shoulder instability.