Genome-wide association study of lifetime cannabis use based on a large meta-analytic sample of 32 330 subjects from the International Cannabis Consortium.

Cannabis is the most widely produced and consumed illicit psychoactive substance worldwide. Occasional cannabis use can progress to frequent use, abuse and dependence with all known adverse physical, psychological and social consequences. Individual differences in cannabis initiation are heritable (40-48%). The International Cannabis Consortium was established with the aim to identify genetic risk variants of cannabis use. We conducted a meta-analysis of genome-wide association data of 13 cohorts (N=32 330) and four replication samples (N=5627). In addition, we performed a gene-based test of association, estimated single-nucleotide polymorphism (SNP)-based heritability and explored the genetic correlation between lifetime cannabis use and cigarette use using LD score regression. No individual SNPs reached genome-wide significance. Nonetheless, gene-based tests identified four genes significantly associated with lifetime cannabis use: NCAM1, CADM2, SCOC and KCNT2. Previous studies reported associations of NCAM1 with cigarette smoking and other substance use, and those of CADM2 with body mass index, processing speed and autism disorders, which are phenotypes previously reported to be associated with cannabis use. Furthermore, we showed that, combined across the genome, all common SNPs explained 13-20% (P<0.001) of the liability of lifetime cannabis use. Finally, there was a strong genetic correlation (rg=0.83; P=1.85 × 10(-8)) between lifetime cannabis use and lifetime cigarette smoking implying that the SNP effect sizes of the two traits are highly correlated. This is the largest meta-analysis of cannabis GWA studies to date, revealing important new insights into the genetic pathways of lifetime cannabis use. Future functional studies should explore the impact of the identified genes on the biological mechanisms of cannabis use.

Comparison of fractionation methods for nitrogen and starch in maize and grass silages.

In in situ nylon bag technique, many feed evaluation systems use a washing machine method (WMM) to determine the washout (W) fraction and to wash the rumen incubated nylon bags. As this method has some disadvantages, an alternate modified method (MM) was recently introduced. The aim of this study was to determine and compare the W and non-washout (D+U) fractions of nitrogen (N) and/or starch of maize and grass silages, using the WMM and the MM. Ninety-nine maize silage and 99 grass silage samples were selected with a broad range in chemical composition. The results showed a large range in the W, soluble (S) and D+U fractions of N of maize and grass silages and the W, insoluble washout (W-S) and D+U fractions of starch of maize silages, determined by both methods, due to variation in their chemical composition. The values for N fractions of maize and grass silages obtained with both methods were found different (p < 0.001). Large differences (p < 0.001) were found in the D+U fraction of starch of maize silages which might be due to different methodological approaches, such as different rinsing procedures (washing vs. shaking), duration of rinsing (40 min vs. 60 min) and different solvents (water vs. buffer solution). The large differences (p < 0.001) in the W-S and D+U fractions of starch determined with both methods can led to different predicted values for the effective rumen starch degradability. In conclusion, the MM with one recommended shaking procedure, performed under identical and controlled experimental conditions, can give more reliable results compared to the WMM, using different washing programs and procedures.

Relationship between chemical composition and in situ rumen degradation characteristics of maize silages in dairy cows.

Several in situ studies have been conducted on maize silages to determine the effect of individual factors such as maturity stage, chop length and ensiling of maize crop on the rumen degradation but the information on the relationship between chemical composition and in situ rumen degradation characteristics remains scarce. The objectives of this study were to determine and describe relationships between the chemical composition and the rumen degradation characteristics of dry matter (DM), organic matter (OM), CP, starch and aNDFom (NDF assayed with a heat stable amylase and expressed exclusive of residual ash) of maize silages. In all, 75 maize silage samples were selected, with a broad range in chemical composition and quality parameters. The samples were incubated in the rumen for 2, 4, 8, 16, 32, 72 and 336 h, using the nylon bag technique. Large range was found in the rumen degradable fractions of DM, OM, CP, starch and aNDFom because of the broad range in chemical composition and quality parameters. The new database with in situ rumen degradation characteristics of DM, OM, CP, starch and aNDFom of the maize silages was obtained under uniform experimental conditions; same cows, same incubation protocol and same chemical analysis procedures. Regression equations were developed with significant predictors (P<0.05) describing moderate and weak relationships between the chemical composition and the washout fraction, rumen undegradable fraction, potentially rumen degradable fraction, fractional degradation rate and effective rumen degradable fraction of DM, OM, CP, starch and aNDFom.

Pleiotropic effects of obesity-susceptibility loci on metabolic traits: a meta-analysis of up to 37,874 individuals.

AIMS/HYPOTHESIS: Genetic pleiotropy may contribute to the clustering of obesity and metabolic conditions. We assessed whether genetic variants that are robustly associated with BMI and waist-to-hip ratio (WHR) also influence metabolic and cardiovascular traits, independently of obesity-related traits, in meta-analyses of up to 37,874 individuals from six European population-based studies. METHODS: We examined associations of 32 BMI and 14 WHR loci, individually and combined in two genetic predisposition scores (GPSs), with glycaemic traits, blood lipids and BP, with and without adjusting for BMI and/or WHR. RESULTS: We observed significant associations of BMI-increasing alleles at five BMI loci with lower levels of 2 h glucose (RBJ [also known as DNAJC27], QPTCL: effect sizes -0.068 and -0.107 SD, respectively), HDL-cholesterol (SLC39A8: -0.065 SD, MTCH2: -0.039 SD), and diastolic BP (SLC39A8: -0.069 SD), and higher and lower levels of LDL- and total cholesterol (QPTCL: 0.041 and 0.042 SDs, respectively, FLJ35779 [also known as POC5]: -0.042 and -0.041 SDs, respectively) (all p < 2.4 × 10(-4)), independent of BMI. The WHR-increasing alleles at two WHR loci were significantly associated with higher proinsulin (GRB14: 0.069 SD) and lower fasting glucose levels (CPEB4: -0.049 SD), independent of BMI and WHR. A higher GPS-BMI was associated with lower systolic BP (-0.005 SD), diastolic BP (-0.006 SD) and 2 h glucose (-0.013 SD), while a higher GPS-WHR was associated with lower HDL-cholesterol (-0.015 SD) and higher triacylglycerol levels (0.014 SD) (all p < 2.9 × 10(-3)), independent of BMI and/or WHR. CONCLUSIONS/INTERPRETATION: These pleiotropic effects of obesity-susceptibility loci provide novel insights into mechanisms that link obesity with metabolic abnormalities.

SERPINE1 -675 4G/5G polymorphism is associated with asthma severity and inhaled corticosteroid response.

Asthma is characterised by chronic airway inflammation and remodelling, which can be (partially) suppressed by inhaled corticosteroids (ICSs). Plasminogen activator inhibitor-1, encoded by the SERPINE1 gene, is the key inhibitor of the plasminogen activator system, which affects tissue repair and remodelling. We studied associations between a functional SERPINE1 -675 4G/5G promoter polymorphism and asthma development, severity and response to ICSs. Longitudinal cohorts of 281 asthmatics and their nonasthmatic spouses, and the general population (n=1,390) were studied. No significant associations were found with asthma development and immunoglobulin (Ig)E levels, or with forced expiratory volume in 1 s (FEV1) in nonasthmatic controls. Asthmatic subjects carrying the SERPINE1 5G allele had higher IgE and lower lung function levels at follow-up, lower maximally attained lung function levels, and faster lung function decline compared with individuals with the 4G/4G genotype. ICS treatment showed an immediate improvement in FEV1 in asthmatics carrying the 5G allele. However, these asthmatics still had the fastest rate of FEV1 decline after initiating ICS treatment. Finally, the 5G allele was associated with a lower prevalence of complete asthma remission at follow-up. These findings suggest that SERPINE1 is not an asthma susceptibility gene, but rather affects the severity, progression and long-term ICS response in asthma.

Gene expression profile, pathways, and transcriptional system regulation in indolent systemic mastocytosis.

BACKGROUND: Mastocytosis is an uncommon disease resulting from proliferation of abnormal mast cells infiltrating skin, bone marrow, liver, and other tissues. The aim of this study was to find differences in gene expression in peripheral blood cells of patients with indolent systemic mastocytosis compared to healthy controls. The second aim was to define a specific gene expression profile in patients with mastocytosis. METHODS: Twenty-two patients with indolent systemic mastocytosis and 43 healthy controls were studied. Whole genome gene expression analysis was performed on RNA samples isolated from the peripheral blood. For amplification and labelling of the RNA, the Illumina TotalPrep 96 RNA Amplification Kit was used. Human HT-12_V3_expression arrays were processed. Data analysis was performed using GeneSpring, Genecodis, and Transcriptional System Regulators. RESULTS: Comparison of gene expression between patients and controls revealed a significant difference (P < 0.05 corrected for multiple testing) and the fold change difference >2 in gene expression in 2303 of the 48.794 analysed transcripts. Functional annotation indicated that the main pathways in which the differently expressed genes were involved are ubiquitin-mediated proteolysis, MAPK signalling pathway, pathways in cancer, and Jak-STAT signalling. The expression distributions for both groups did not overlap at all, indicating that many genes are highly differentially expressed in both groups. CONCLUSION: We were able to find abnormalities in gene expression in peripheral blood cells of patients with indolent systemic mastocytosis and to construct a gene expression profile which may be useful in clinical practice to predict the presence of mastocytosis and in further research of novel drugs.

Gene expression analysis predicts insect venom anaphylaxis in indolent systemic mastocytosis.

BACKGROUND: Anaphylaxis to insect venom (Hymenoptera) is most severe in patients with mastocytosis and may even lead to death. However, not all patients with mastocytosis suffer from anaphylaxis. The aim of the study was to analyze differences in gene expression between patients with indolent systemic mastocytosis (ISM) and a history of insect venom anaphylaxis (IVA) compared to those patients without a history of anaphylaxis, and to determine the predictive use of gene expression profiling. METHODS: Whole-genome gene expression analysis was performed in peripheral blood cells. RESULTS: Twenty-two adults with ISM were included: 12 with a history of IVA and 10 without a history of anaphylaxis of any kind. Significant differences in single gene expression corrected for multiple testing were found for 104 transcripts (P < 0.05). Gene ontology analysis revealed that the differentially expressed genes were involved in pathways responsible for the development of cancer and focal and cell adhesion suggesting that the expression of genes related to the differentiation state of cells is higher in patients with a history of anaphylaxis. Based on the gene expression profiles, a naïve Bayes prediction model was built identifying patients with IVA. CONCLUSIONS: In ISM, gene expression profiles are different between patients with a history of IVA and those without. These findings might reflect a more pronounced mast cells dysfunction in patients without a history of anaphylaxis. Gene expression profiling might be a useful tool to predict the risk of anaphylaxis on insect venom in patients with ISM. Prospective studies are needed to substantiate any conclusions.

Coeliac disease-associated risk variants in TNFAIP3 and REL implicate altered NF-kappaB signalling.

OBJECTIVE: Our previous coeliac disease genome-wide association study (GWAS) implicated risk variants in the human leucocyte antigen (HLA) region and eight novel risk regions. To identify more coeliac disease loci, we selected 458 single nucleotide polymorphisms (SNPs) that showed more modest association in the GWAS for genotyping and analysis in four independent cohorts. DESIGN: 458 SNPs were assayed in 1682 cases and 3258 controls from three populations (UK, Irish and Dutch). We combined the results with the original GWAS cohort (767 UK cases and 1422 controls); six SNPs showed association with p<1 x 10(-04) and were then genotyped in an independent Italian coeliac cohort (538 cases and 593 controls). RESULTS: We identified two novel coeliac disease risk regions: 6q23.3 (OLIG3-TNFAIP3) and 2p16.1 (REL), both of which reached genome-wide significance in the combined analysis of all 2987 cases and 5273 controls (rs2327832 p = 1.3 x 10(-08), and rs842647 p = 5.2 x 10(-07)). We investigated the expression of these genes in the RNA isolated from biopsies and from whole blood RNA. We did not observe any changes in gene expression, nor in the correlation of genotype with gene expression. CONCLUSIONS: Both TNFAIP3 (A20, at the protein level) and REL are key mediators in the nuclear factor kappa B (NF-kappaB) inflammatory signalling pathway. For the first time, a role for primary heritable variation in this important biological pathway predisposing to coeliac disease has been identified. Currently, the HLA risk factors and the 10 established non-HLA risk factors explain approximately 40% of the heritability of coeliac disease.

No association between the Arg201Gly polymorphism of the DCC gene and colorectal cancer.

BACKGROUND AND AIMS: In one small study, the DCC Arg201Gly polymorphism has been observed more frequently in colorectal cancer cases compared with controls. We wondered whether these results could be replicated in a much larger study. METHODOLOGY: The DCC Arg201 Gly polymorphism was genotyped in 625 unselected Caucasian colorectal cancer patients and 220 controls. Association analysis was used to search for a difference between patients and controls. Subgroup analyses were performed for site of tumour, gender, age at diagnosis, family history of colorectal cancer and modified Dukes classification. RESULTS: The association analyses revealed no difference in Arg201Gly genotype frequency between patients and controls, neither overall nor for different subgroups according to site of tumour, gender, age at diagnosis, family history of colorectal cancer and modified Dukes classification. CONCLUSION: No association was observed between the Arg201Gly polymorphism of DCC and colorectal cancer risk.

Mapping of a susceptibility gene for multiple sclerosis to the 51 kb interval between G511525 and D6S1666 using a new method of haplotype sharing analysis.

Multiple sclerosis (MS) is a complex disease that is partly genetic in origin. Although an association of MS with specific human leukocyte antigen (HLA) types has been known for almost 30 years, the nature of this relationship has remained unclear. Furthermore, genetic resolution sufficient to implicate a specific gene in the HLA region has not been achieved. Many loci in the HLA region have been found to be significantly associated with MS, which is largely explained by the extended haplotype sharing and varying marker informativity of the region. We have determined 248 haplotypes of MS patients from the population of the northern Netherlands and 226 haplotypes of their relatives as controls using a set of 22 microsatellite markers covering the HLA region. The data were analyzed using standard association methods and a new statistical method, haplotype sharing statistics (HSS). Haplotype sharing statistics determines the extent of haplotype sharing for all pairs of haplotypes of patients and of controls and calculates the difference in mean haplotype sharing between patients and controls. Haplotype sharing was found to be significantly greater among patients than among controls in a region of 1.1 Mb between markers G511525 and TNFalpha. The involvement of this region is also supported by association analysis and the transmission/disequilibrium test (TDT). Within this region, HSS, which is largely independent of association and TDT, indicated the interval of 51 kb between G511525 and D6S1666 as that most likely to contain a susceptibility gene for MS. As DQB1 is the sole gene known in this interval at present, the results of our analysis suggest that this gene plays a role in the pathogenesis of MS.

Molecular cloning of a new angiopoietinlike factor from the human cornea.

PURPOSE: To isolate tissue-specific gene products that contribute to corneal integrity. METHODS: A cDNA library was constructed and differentially hybridized. Cornea-specific clones were purified and further characterized. RESULTS: In this study cornea-specific gene products were isolated by differential cDNA hybridization. In addition to known cornea-specific gene products, a transcript was isolated coding for a protein homologous to the angiopoietins, a recently described family of (anti)angiogenic factors. Subsequently, the full cDNA was sequenced, and the identified open reading frame was named cornea-derived transcript 6 (CDT6). Similar to the angiopoietins, CDT6 contains a hydrophobic NH2-terminal sequence, a coiled-coil domain, and a COOH-terminal fibrinogenlike domain. Expression of CDT6 could be detected only in the cornea and not in several other adult human tissues. Within the cornea, expression of CDT6 is confined to the stromal layer. CONCLUSIONS: The human cornea shows high-level expression of a gene product homologous to the (anti)angiogenic factors, the angiopoietins. This homology, together with stromal-specific expression, suggests that this factor may contribute to the avascularity of the human cornea.

Cytomegalovirus (CMV) strain differences between the eye and blood in AIDS patients with CMV retinitis.

OBJECTIVE: To investigate possible differences in cytomegalovirus (CMV) strain distribution between the eye and blood in AIDS patients with CMV retinitis. METHODS: CMV DNA sequences from aqueous humour and peripheral blood leukocytes (PBL), obtained from 13 AIDS patients with CMV retinitis, were compared. DNA was isolated and the CMV IE-1 sequence (part of the immediate early-1 gene) and the a-sequence (located in the a-region) were amplified by polymerase chain reaction (PCR). The PCR products of the a-sequence were analysed by Southern blotting for amplified fragment-length polymorphisms. The level of divergence between the a-sequences of aqueous humour- and PBL-derived CMV was studied in two patients by cloning these sequences followed by sequence analysis. RESULTS: CMV DNA could be detected in all aqueous humour samples and in 10 out of 13 paired blood samples. In the 10 patients, with CMV DNA detectable in both aqueous humour and PBL, seven cases showed differences between the amplified products of both compartments. Sequence analysis in two patients revealed that the aqueous humour and PBL of the same patient can harbour both identical, similar and highly divergent CMV a-sequences. CONCLUSION: These results indicate that despite the haematogenous spread of CMV, the eye, being a relatively shielded organ, may contain CMV strains different from those found in the blood.

Cytomegalovirus glycoprotein B genotyping in ocular fluids and blood of AIDS patients with cytomegalovirus retinitis.

PURPOSE: To determine the frequency of cytomegalovirus glycoprotein B (gB) genotypes in clinical samples of ocular fluids of patients with acquired immune deficiency syndrome (AIDS) who have cytomegalovirus retinitis and to compare these with the cytomegalovirus gB genotype in paired peripheral blood leukocytes. METHODS: Glycoprotein B genotypes of cytomegalovirus genomic DNA were determined in 29 ocular and 9 paired blood samples of 27 patients, by polymerase chain reaction amplification followed by restriction fragment length polymorphism analysis. RESULTS: In the 29 ocular samples, 30 gB genotypes were determined: Glycoprotein B1 was found in 8 samples (27%), gB2 in 9 samples (30%), gB3 in 6 samples (20%), and gB4 in 3 samples (10%). In one sample, a mixed genotype was observed. In addition to these previously characterized gB genotypes, a new gB variant was observed in the ocular fluid of four patients. Partial sequence analysis revealed that this new gB genotype is closely related to gB3, and it was therefore named gB3'. In the blood samples, only gB1, gB2, and gB3 genotypes were observed. In the nine paired samples of ocular fluid and blood, four showed a difference in gB genotype between these compartments. CONCLUSIONS: The distribution of cytomegalovirus glycoprotein B genotypes gB1-gB4 in ocular fluids of patients with AIDS who have cytomegalovirus retinitis was determined in this study. The predominance of gB2, as described by others, was not confirmed. The glycoprotein B genotype in the eye can be different from the genotype found in the blood of the same patient. A new gB variant, gB3', was found in the ocular samples of 4 of 27 patients, but not in the blood samples tested.

Increased presence of Epstein-Barr virus DNA in ocular fluid samples from HIV negative immunocompromised patients with uveitis.

AIMS: To investigate whether routine testing for Epstein-Barr virus (EBV) is necessary in the examination of a patient with uveitis. METHODS: Intraocular EBV DNA was determined in 183 ocular fluid samples taken from patients with AIDS and uveitis, HIV negative immunocompromised uveitis, acute retinal necrosis, toxoplasma chorioretinitis, intraocular lymphoma, anterior uveitis, and miscellaneous uveitis of unknown cause. In 82 samples from this group of patients paired serum/ocular fluid analysis was performed to detect local antibody production against EBV. Controls (n = 46) included ocular fluid samples taken during surgery for diabetic retinopathy, macular pucker, or cataract. RESULTS: Serum antibody titres to EBV capsid antigen proved to be significantly increased in HIV negative immunocompromised patients with uveitis (p < 0.01) compared with controls. Local antibody production revealed only three positive cases out of 82 patients tested, two results were borderline positive and one patient had uveitis caused by VZV. EBV DNA was detected in three out of 46 control ocular fluid samples. In the different uveitis groups EBV DNA was noted, but was not significantly higher than in the controls, except in six out of 11 HIV negative immunocompromised patients (p = 0.0008). In four out of these six cases another infectious agent (VZV, HSV, CMV, or Toxoplasma gondii) had previously been identified as the cause of the uveitis. CONCLUSIONS: When comparing various groups of uveitis patients, EBV DNA was found more often in HIV negative immunocompromised patients with uveitis. Testing for EBV does not have to be included in the routine management of patients with uveitis, since indications for an important role of this virus were not found in the pathogenesis of intraocular inflammation.

Twenty years' delay of fellow eye involvement in herpes simplex virus type 2-associated bilateral acute retinal necrosis syndrome.

PURPOSE: To describe a case of acute retinal necrosis with concurrent encephalitis and determine the causative virus. The patient had a history of presumed acute retinal necrosis in the left eye at the age of 8 years and recurrent genital herpes. METHODS: Diagnostic anterior chamber puncture of the eye and lumbar puncture for laboratory analysis. RESULTS: Polymerase chain reaction identified herpes simplex virus type 2 in the eye, and local antibody production to herpes simplex virus was demonstrated in the aqueous of this eye and in the cerebrospinal fluid. CONCLUSION: Herpes simplex virus type 2 may cause bilateral acute retinal necrosis with long delay of fellow eye involvement and concurrent encephalitis.

Serological and polymerase chain reaction-based analysis of aqueous humour samples in patients with AIDS and necrotizing retinitis.

OBJECTIVE: To evaluate the measurement of intraocular antibody production and detection of DNA by the polymerase chain reaction (PCR) for diagnosis of the causative microorganism in patients with AIDS and necrotizing retinitis. METHODS: Paired serum and aqueous humour samples obtained from 28 patients with AIDS and necrotizing retinitis, seen between January 1987 and March 1992, were analysed for intraocular antibody production against cytomegalovirus (CMV), varicella zoster virus, herpes simplex virus, Epstein-Barr virus, and Toxoplasma gondii. Specific antibody titres in the inflamed eye and in the circulation were related to total immunoglobulin G content in the aqueous humour and serum. In addition, PCR analysis was performed in 15 samples. Results were compared to the final diagnosis, which was based on the subsequent clinical course. Results were also related to parameters describing the immune state of the patients: CD4 count, time between diagnosis of an AIDS-defining illness and retinitis, and time of survival following the diagnosis of retinitis. RESULTS: In 11 (39%) out of 28 patients we found local intraocular antibody production which correlated with the final diagnosis (one out of two cases with acute retinal necrosis, three out of five cases with toxoplasma retinitis, and eight out of 21 patients with CMV retinitis). In all 13 patients with CMV retinitis PCR analysis detected CMV DNA. In one patient with the clinical diagnosis of Toxoplasma retinitis, Toxoplasma DNA could be determined, whereas in the same sample CMV DNA was also found. In yet another patient with Toxoplasma retinitis only CMV DNA could be detected. A relationship between results of local antibody determination with either CD4 counts, or the time interval between AIDS-defining illness and retinitis, or survival time after diagnosis of retinitis could not be established. CD4 counts were higher than 50 x 10(6)/l in eight out of 19 patients with CMV retinitis. No complications of paracentesis were seen. CONCLUSIONS: Detection of intraocular antibody production and PCR analysis are quick and safe procedures and helpful tools for diagnosis of the involved pathogen in AIDS patients with a necrotizing retinitis. Negative results of local antibody production, even in the presence of detectable viral DNA, could not be related to the parameters of a more deteriorated immune status of these patients.

Serologic and polymerase chain reaction analysis of intraocular fluids in the diagnosis of infectious uveitis.

PURPOSE: Infectious uveitis entities are usually rapidly progressive blinding diseases that can be prevented by prompt administration of specific antimicrobial therapy. With the aim of improving early diagnosis in patients with infectious uveitis, intraocular fluid samples from patients with sight-threatening posterior uveitis were investigated to determine the causative agent. METHODS: Thirty-eight patients with acquired immunodeficiency syndrome (AIDS) and retinitis, eight immunosuppressed patients with retinitis, 16 immunocompetent patients with acute retinal necrosis, and 22 immunocompetent patients with toxoplasmic retinochoroiditis were analyzed by polymerase chain reaction for the presence of herpesviruses and Toxoplasma gondii DNA and for local antibody production against these microorganisms. RESULTS: In patients with AIDS and retinitis, polymerase chain reaction was positive for cytomegalovirus DNA in 21 (91%) of the 23 ocular fluid samples obtained during active cytomegalovirus retinitis, whereas local antibody production analysis was negative in all cases. In acute retinal necrosis, varicella-zoster virus or herpes simplex virus could be established as the inciting agent in 81% of the cases, using the combination of both techniques. Polymerase chain reaction was positive in all samples obtained within two weeks after the onset of disease. Toxoplasma gondii DNA was detected in 4 of 13 samples (31%) from immuno-competent patients with active toxoplasmic retinochoroiditis; in each case, local antibody production was also detected. In contrast, no local antibody production was observed in two of three samples from transplant recipients that were positive for T. gondii DNA. All the control samples tested were negative for the above-mentioned tests. CONCLUSIONS: In patients with AIDS, polymerase chain reaction analysis is preferable above local antibody production in detecting the inciting agent of retinitis. In other cases, the combination of both techniques can make a valuable contribution to the diagnosis.