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Biomedical subjects

A M Johnson

Publications and source records attributed to A M Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Sexual lifestyles and HIV risk.

Britain's first large, national survey of sexual attitudes and lifestyles will allow improved estimates of the magnitude of the HIV epidemic in Britain and should lead to better strategies for prevention.

Adolescent↗
PubMed1992

Intracranial aneurysms in autosomal dominant polycystic kidney disease.

BACKGROUND AND METHODS: Intracranial aneurysms are a feature of autosomal dominant polycystic kidney disease, but their prevalence is uncertain. We studied 92 subjects with autosomal dominant polycystic kidney disease who had no symptoms or signs of any neurologic disorder. To determine the prevalence of intracranial aneurysms, we performed high-resolution computed tomography (CT) in 60 subjects, four-vessel cerebral angiography in 21, and both procedures in 11. RESULTS: Four of the 88 subjects in whom the radiologic studies were successfully completed had intracranial aneurysms (4 percent; 95 percent confidence interval, 0.1 to 9 percent), as compared with the prevalence of 1 percent reported for an angiographic study of the general population. Three of the four subjects had multiple aneurysms. Seven subjects for whom the results of CT studies were suspicious underwent cerebral angiography: two had aneurysms, and five had normal vascular structures that accounted for the suspicious results of tomography. Four subjects who had normal CT imaging studies also had normal angiographic examinations. Eight of the 32 subjects who underwent angiography (25 percent) had transient complications, as compared with 22 of 220 control subjects (10 percent) who did not have polycystic kidney disease (P less than 0.05). We could not identify any risk factor in these subjects that was related to the occurrence of aneurysm. CONCLUSIONS: Asymptomatic intracranial aneurysms appear to be more frequent in people with polycystic kidney disease than in the general population, although our 95 percent confidence interval includes the possibility of no difference. Because cerebral angiography is associated with increased morbidity in people with polycystic kidney disease, we recommend high-resolution CT as a screening test.

Adolescent↗
PubMed1992

Comparison of in vitro translation products of Sarcocystis gigantea and Sarcocystis tenella.

Poly(A)+ RNA was purified from cystozoites of Sarcocystis gigantea and Sarcocystis tenella and used to in vitro translate polypeptides in a wheat germ and a rabbit reticulocyte translation system. The in vitro translated polypeptides were compared by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The S. tenella mRNA translated at least two polypeptides (mol. wt about 80,000 and 21,500) in both translation systems that were not translated by the S. gigantea mRNA. To study co-translational and initial post-translational processing in Sarcocystis, the poly(A)+ RNA preparations were in vitro translated in the rabbit reticulocyte translation system in the presence or absence of canine microsomal membranes. Based on electrophoresis, there appeared to be modification of at least some Sarcocystis polypeptides in the mol. wt range 17,000-30,000. In addition, the translation products were immunoprecipitated with a homologous and a heterologous antiserum. The immunoprecipitated polypeptides were compared by electrophoresis and the S. tenella translation products contained at least one unique antigenic polypeptide with a mol. wt of about 34,700 that was not processed by the microsomal membranes. These results suggest that there is at least one polypeptide that is a candidate for use as an antigen for the differentiation of S. gigantea and S. tenella infections in sheep.

Animals↗
PubMed1992

Phylogenetic relationships of Sarcocystis species from sheep, goats, cattle and mice based on ribosomal RNA sequences.

Partial sequences of the small subunit ribosomal RNA of four species of Sarcocystis were obtained by reverse transcription of total cellular RNA. The semi-conserved regions of these four species were aligned with homologous sequences of two other Sarcocystis species and a range of other eukaryotes including Toxoplasma, Eimeria and Cryptosporidium. Parsimony analysis of the aligned sequences showed that Sarcocystis and Toxoplasma had a more recent common ancestor with Eimeria than with Cryptosporidium. The six Sarcocystis spp. did not cluster together in this analysis; two monophyletic groups were observed, one formed by the two Sarcocystis spp. with felids as definitive hosts, and another by the four Sarcocystis spp. with canids as definitive hosts. These two clades were segregated by Toxoplasma. An analysis of nucleotide divergence suggests that the difference between the two groups of Sarcocystis spp. is similar to that between invertebrates and vertebrates. The results obtained here question the validity of a separation of the genus Sarcocystis from Toxoplasma and refute classifications that place these two genera into two different subfamilies of the Sarcocystidae.

Animals↗
PubMed1992

Ribosomal DNA sequence comparison of Babesia and Theileria.

Previous studies on the taxonomy of Babesia spp. (phylum Apicomplexa) using morphological and life cycle characteristics have resulted in their classification into 3 subgenera, with the genus Theileria being most closely related to them. Using a strategy based on the direct sequence analysis of products derived by asymmetric PCR to determine the nucleotide sequences, we have tested the validity of this classification by sequencing the small subunit ribosomal RNA genes amplified from 2 Babesia species, namely Babesia bovis and Babesia rodhaini, and comparing these with previously published sequences of Theileria annulata and Babesia bigemina using Plasmodium falciparum as an outgroup. The results of this phylogenetic analysis support the recognition of at least 2 genera in Babesia--one to include B. bigemina and B. bovis, the other to include B. rodhaini.

Animals↗
PubMed1992

Development of ELISAs based on recombinant antigens for the detection of Toxoplasma gondii-specific antibodies in sheep and cats.

ELISAs using recombinant parasite polypeptides as antigens were developed to measure Toxoplasma gondii-specific antibodies in the sera of sheep and cats. Compared with an ELISA based on traditional parasite antigen, the ELISA for sheep sera had a sensitivity of 79% and a negative predictive value of 80%, and the ELISA for cat sera had a sensitivity of 100% and a negative predictive value of 100%. Both ELISAs had specificities of 100% and positive predictive values of 100%. These ELISAs appear to be a useful cost-effective alternative to ELISAs based on traditional parasite antigen for the measurement of T. gondii-specific antibodies in the sera of sheep and cats.

Animals↗
PubMed1992

Clinical profiles of gross hematuria in autosomal dominant polycystic kidney disease.

There is little information on the characteristics, management, or sequelae of gross hematuria in autosomal dominant polycystic kidney disease (ADPKD). Therefore, we obtained detailed information regarding gross hematuria in 191 adult ADPKD subjects. Forty-two percent (N = 81) experienced at least one episode of gross hematuria. The mean age of the initial episode was 30 +/- 1 years; only 10% of subjects reported the first episode before age 16. Twenty-three percent of those with gross hematuria had experienced more than six occurrences. Sixty-two percent of patients with bleeding indicated a presumptive precipitating event, most commonly urinary tract infection (42% overall, 61% of females v 17% of males, P less than 0.01), or sports or strenuous activity (20% of males v 11% of females, NS). In 56% of subjects, the episode persisted for 2 to 7 days. Hypertensive ADPKD subjects were more likely to have gross hematuria than normotensive subjects (48% v 30%, P less than 0.02) and those with gross hematuria had larger renal size (820 +/- 87 v 588 +/- 52 cm3, P less than 0.03). Moreover, those subjects with more episodes of gross hematuria had a higher serum creatinine concentration than those with fewer episodes (serum creatinine: 0 episodes, 120 +/- 10 v greater than 5 episodes, 190 +/- 30 mumol/L, P less than 0.04 [1.4 +/- 0.1 v 2.1 +/- 0.3 mg/dL]). This association suggests that, although self-limited, cumulative episodes of gross hematuria may have an unfavorable impact on long-term renal function.

Adolescent↗
PubMed1992

Factors affecting the progression of renal disease in autosomal-dominant polycystic kidney disease.

Autosomal-dominant polycystic kidney disease results in renal failure at a varying age from childhood to old age. We postulated that factors other than the culprit gene alone contribute to the course of progression of the renal failure. We studied 580 subjects with autosomal-dominant polycystic kidney disease and 194 unaffected family members. We calculated survival curves to end-stage renal failure or death and developed a linear model for testing the effects of single or multiple variables on the progression of renal failure as estimated from the reciprocal of serum creatinine. Fifty-two subjects died and 94 reached end-stage renal failure during the period of observation, yielding functional survivals of 71% at age 50 years, 53% at 58 years and 23% at 70 years. The following variables were independently associated with worse mean renal function at a given age (P value less than 0.01): the PKD1 gene, younger age at diagnosis, male gender, hypertension, increased left ventricular mass, hepatic cysts in women, three or more pregnancies, gross hematuria, urinary tract infections in men and renal size expressed as renal volume. The following were not associated significantly with the course of renal function: gender of affected parent, mitral valve prolapse, intracranial aneurysms, any pregnancy, hepatic cysts in men and urinary tract infections in women. The identification of unalterable maleficent factors such as the PKD1 gene and male gender permit more informed counseling while the identification of alterable factors such as hypertension, number of pregnancies and recurrent urinary tract infections provides the clinician with the opportunity to modify these factors and improve the management of patients with autosomal-dominant polycystic kidney disease.

Adult↗
PubMed1992

Nonrandom distribution of chloroplast recombination events in Chlamydomonas reinhardtii: evidence for a hotspot and an adjacent cold region.

Intermolecular recombination of Chlamydomonas chloroplast genes has been analyzed in sexual crosses and following biolistic transformation. The pattern and position of specific exchange events within 15 kb of the 22-kb inverted repeat have been mapped with respect to known restriction fragment length polymorphism markers that distinguish the chloroplast genomes of the interfertile species Chlamydomonas reinhardtii and Chlamydomonas smithii. Recombinant progeny were selected from two- and three-factor crosses involving point mutations conferring herbicide (dr) and antibiotic resistance (er and spr) in the psbA, 23S and 16S ribosomal RNA genes, respectively. Exchange events were not randomly distributed over the 15-kb region, but were found to occur preferentially in a 0.7-kb sequence spanning the 3' end of the psbA gene and were much less common in an adjacent region of ca. 2.0 kb. These findings are corroborated by data showing that the dr mutation is unlinked genetically (3% recombination/kb) to the er and spr rRNA mutations, which are themselves linked and show ca. 1% recombination/kb. This discrepancy is significant since the dr-er and er-spr intervals are about the same length (ca. 7 kb). During chloroplast transformation, the 0.7-kb recombination hotspot also functions as a preferential site for exchange events leading to the integration of donor psbA gene sequences. The 0.7-kb hotspot region contains four classes of 18-37-bp direct repeats also found in other intergenic regions, but no open reading frame. Using deletion constructs in a chloroplast transformation assay, the hotspot was localized to a 500-bp region that lacks most of these repeats, which suggests that the repeats themselves are not responsible for the increased recombination frequency. Within this region, a 400-bp sequence is highly conserved between the chloroplast genomes of C. reinhardtii and C. smithii and includes several structural motifs characteristic of recombination hotspots in other systems.

Animals↗
PubMed1992

Virulence and adhesive properties of serotypes A and B of Candida albicans isolated from paediatric burn patients.

The virulence and adhesive properties of 50 isolates of Candida albicans serotypes A and B collected over 6 years from 48 paediatric burn patients were examined to provide more detailed information about candidal pathogenesis in burn patients and to examine the relevance of the commonly used epithelial cell adhesion assay for determining fungal virulence. The isolates represented a fair distribution of serotypes (29 isolates were serotype A and 21 isolates were serotype B) and a total of 28 serotype-biotype combinations were found; 32% of the serotype-biotype combinations appeared only once, while 44% of the isolates showed similar biotype tests for two of three digits. Adhesion of the isolates to plastic and to buccal epithelial cells (BECs) was examined and compared after growth in a chemically defined medium. There were significant differences in the adhesion of individual isolates to plastic or BECs, but no correlation was found between biotype and adhesiveness. Serotype B isolates were found to be more adhesive to BECs (p less than 0.05) but not to plastic. There was no apparent correlation between candidal adhesiveness and site of isolation from these patients (autografts, blood, faeces, throat swabs, tracheal aspirates, wounds and intravenous catheters), although isolates from catheters were generally less adhesive to epithelial cells. Virulence in a systemic infection mouse model revealed that there were significant differences in virulence between isolates, but no correlation was found between virulence and the biotype, serotype or site of isolation. Similarly, no correlation was found between virulence and adhesiveness or cell-surface hydrophobicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Evaluation of a recombinant antigen ELISA for the diagnosis of acute toxoplasmosis and comparison with traditional antigen ELISAs.

An evaluation of five ELISA methods for the diagnosis of acute toxoplasmosis was undertaken by comparing a laboratory-produced ELISA employing two recombinant Toxoplasma gondii polypeptides as antigen with a laboratory-produced ELISA and three commercially available ELISAs employing traditional parasite antigen preparations derived from whole tachyzoites. With a panel of 75 sera from patients who showed either serological and clinical evidence of acute toxoplasmosis, or of diseases caused by other infectious agents, or from patients who showed no evidence of infectious disease, the ELISAs gave overall positive predictive values of 81.6-100%, negative predictive values of 87.8-100%, sensitivities of 81.3-100%, and specificities of 83.7-100%. No two ELISAs gave identical results with all sera tested. In total, the ELISA based on the two recombinant T. gondii polypeptides appeared to be the most specific ELISA in this comparison, showing positive predictive values and specificities of 100% for all groups of patients tested. The overall negative predictive value for this ELISA was 87.8% and the sensitivity was 81.3%. Therefore, the ELISA based on recombinant antigen appears to be a promising advance in the serological diagnosis of acute toxoplasmosis.

Acute Disease↗
PubMed1992

Partial characterization of a cell-free hemolytic factor produced by Helicobacter pylori.

Maximum cell-free hemolytic activity of helicobacter pylori cultured in broth containing 10% horse serum occurred only after the stationary phase of growth was reached, unlike many hemolysins produced by Gram-negative bacteria which are active during exponential growth. This characteristic of the H. pylori hemolytic factor suggested that it might also possess protease activity. However, because no evidence of albumin degradation was found, the hemolysis by cell-free concentrates of H. pylori appears to be due to a unique factor derived from the organism. Because variable hemolysis results were obtained with culture broths lacking albumin or serum, these proteins may act as carriers or stabilizers of the putative hemolysin.

Dose-Response Relationship, Immunologic↗
PubMed1992

Auditing AIDS reporting. Experience from a central London district 1982-1991.

OBJECTIVE: To evaluate completeness of reporting of cases of AIDS to the Communicable Disease Surveillance Centre (CDSC) between 1982-1991. SETTING: Southside of the Bloomsbury and Islington District Health Authority. DESIGN: Reconciliation exercise with CDSC of cases reported with those known to have received treatment in the district from 1982 to March 1990. Case note review of unreported cases and follow-up at March 1991. MAIN OUTCOME MEASURES: Delayed and non-reporting of cases. RESULTS: Cumulatively 13% (46/351) of patients whose initial AIDS illness was diagnosed in the District remained unreported by March 1991. Non-reporting increased from 9% (2/23) of cases diagnosed prior to 1985 to 28% (26/92) of cases diagnosed between 1989 and 1990. After September 1987 the proportion of patients with a diagnosis of Pneumocystis carinii pneumonia or Kaposi's sarcoma was significantly higher in the reported group than in the non-reported group: 78% (124/158) v 51% (24/49) p < 0.001. Nine of 19 (47%) cases of AIDS transferring their care into the district had not been reported by their previous District Health Authority. CONCLUSIONS: Within the district non-reporting of cases of AIDS has risen over time as the numbers of patients treated has increased. The physician must be aware of the full AIDS case definition for surveillance purposes and the implications of non-reporting for the allocation of special "ring-fenced" resources for AIDS care. Adequate investment in information and reporting systems would seem essential.

Acquired Immunodeficiency Syndrome↗