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Biomedical subjects

A M Johnson

Publications and source records attributed to A M Johnson.

At least 181 records · Page 10Linked to original sources
PubMed1994

The phylogenetic relationships of Kronborgia (Platyhelminthes, Fecampiida) based on comparison of 18S ribosomal DNA sequences.

Approximately 580 bp at the 5' end of the small subunit RNA gene were amplified by PCR for 19 platyhelminth taxa, and Homo and Artemia were used as outgroups. These were analysed to test the hypothesis that fecampiids and Neodermata are sister groups. No evidence was found that the fecampiid Kronborgia isopodicola is closely related to the Neodermata or to the Rhabdocoela (in which the fecampiids are usually included). Morphological, including ultrastructural, characters and DNA data do not support a close relationship of fecampiids with any other platyhelminth taxon, although the DNA sequence analysis provides some evidence that the Acoela and Tricladida are closest. Fecampiids are sufficiently different from any other platyhelminth group to warrant establishment of a class, Fecampiida, for them. A diagnosis of the new class is given.

Animals↗
PubMed1994

The phylogeny of Neospora caninum.

Morphological studies by electron microscopy on the protozoan Neospora caninum have shown that this organism possesses a subcellular structure typical of parasites classified in the family Sarcocystidae, subclass Coccidiasina of the phylum Apicomplexa. Using a strategy based on DNA sequence analysis of products derived by asymmetric PCR to determine the nucleotide sequences, we have tested the validity of this classification by comparing the small subunit ribosomal RNA (18S rRNA) gene sequences of N. caninum with those of other parasitic protozoa classified in the phylum Apicomplexa. The results of this analysis confirm the placing of N. caninum in the family Sarcocystidae and place it as a sister group to Toxoplasma gondii in the phylum Apicomplexa.

Animals↗
PubMed1994

ELISAs based on recombinant antigens for seroepidemiological studies on Toxoplasma gondii infections in cats.

Two recombinant Toxoplasma gondii polypeptides, H4 and H11, were tested as diagnostic antigens in enzyme-linked immunosorbent assays (ELISAs). The results obtained by ELISAs based on single H4 (H4-ELISA), on single H11 (H11-ELISA) and on a mixture of H4 and H11 (H4/H11-ELISA) were compared with results obtained by an ELISA based on traditional ELISA antigen (TEA-ELISA), an indirect fluorescent antibody test (IFAT), the Sabin-Feldman dye test (SFDT) and a direct agglutination test (DAT). A total of 306 cats from a suburban cat population were tested of which about 45% showed serological evidence of T. gondii infection. Infection rates varied from about 32% for cats kept indoors to about 55% for stray cats. Specificities > 99% were observed for all ELISAs based on the recombinant antigens (H4-ELISA, H11-ELISA and H4/H11-ELISA). The H4/H11-ELISA also reached a sensitivity of 95% which compared very favourably with those observed for the TEA-ELISA (98%) and for the IFAT (94%). Negative and positive predictive values for the H4/H11-ELISA were 96 and > 99%, respectively. Antibody titres measured by the H4/H11-ELISA also correlated well with those measured by the SFDT and the DAT. Hence, the H4/H11-ELISA appears to be a very suitable test for sero-epidemiological studies on T. gondii infections in cats.

Age Factors↗
PubMed1994

Codon usage and bias among individual genes of the coccidia and piroplasms.

Codon usage has been analysed in individual gene sequences, derived from a variety of parasitic protozoa in the class Sporozoa of the phylum Apicomplexa using metric multidimensional scaling. The two groups of codon usage patterns detected reflect the two main subgroups of organisms studied (the coccidia and the piroplasms), and it is the pattern of usage of synonymous codons that has the largest influence on overall codon usage in the individual genes, rather than being the pattern of amino acid composition of the gene product. The magnitude of the codon usage bias in the sequences was determined using three commonly used indices-NC, GC3S and B. In general, although relatively low levels of codon usage bias were detected in these gene sequences, codon usage bias does explain at least some of the codon usage patterns observed. Codon usage bias was observed to be dependent on the overall base composition of the genes analysed, which in turn was reflected in the types of codons that were either over- or under-represented in the nucleotide sequences. In keeping with observations on prokaryotic organisms, it is speculated that the codon usage patterns detected in these parasitic protozoa are the result of directional mutation pressure on the base composition of the genomic DNA.

Animals↗
PubMed1994

Is there evidence for anticipation in autosomal-dominant polycystic kidney disease?

The heritability of autosomal-dominant polycystic kidney disease (ADPKD) is marked by an apparent high mutation rate, neonatal onset of disease in some patients and intrafamily variability. These findings raise the possibility of genetic anticipation in ADPKD as has been observed in fragile-X syndrome, myotonic dystrophy and Huntington's disease. We reviewed 242 pedigrees obtained during our prospective studies on the natural history of ADPKD. Anticipation was defined as a 10 year earlier onset of ESRD in offspring as compared to their affected parent or a child diagnosed in the first year of life. Due to the slowly progressive nature of ADPKD, 148 pedigrees were uninformative. Anticipation of ESRD was found in 49% of informative families in at least one parent-offspring pair, and when early onset children were included, 53% of informative families had at least one parent-offspring pair with anticipation. Moreover, the transmitting parent in the pairs with anticipation was more often the mother than the father, similar to myotonic dystrophy, where the most dramatic form of anticipation, congenital disease, occurs almost exclusively with maternal transmission. These observations suggest that ADPKD may be another genetic disorder characterized by heritable unstable DNA.

Adolescent↗
PubMed1994

Risk behaviour and HIV prevalence in international travellers.

OBJECTIVE: To assess risk factors for infection and to determine HIV prevalence in a sample of international travellers. DESIGN: A cross-sectional survey of new patients attending a hospital outpatient clinic, and self-completion of an anonymous questionnaire on sexual behaviour prior to and during travel. Urine samples were tested for the presence of antibodies to HIV. SETTING: The Hospital for Tropical Diseases, London, UK. SUBJECTS: All new patients over a 6-month period. RESULTS: Of 782 people approached, 757 (97%) agreed to participate: 141 (18.6%) had had new sexual partners during their most recent trip abroad. Almost two-thirds of those having sex abroad did not use condoms on every occasion with a new partner, and 5.7% contracted a sexually transmitted disease (STD) during their most recent trip; 26% of men from World Health Organization Pattern I countries who had new sexual partners abroad paid for sex. Sixteen out of 731 (2.2%) participants were HIV-antibody-positive. HIV positivity was associated with being born in east, central or southern Africa, having symptoms of an STD since arriving in the United Kingdom and being treated for an STD since arrival. CONCLUSION: The rates of unsafe sex and payment for sex abroad reported by these international travellers indicate the potential for contracting and transmitting STD, including HIV, in both their foreign and domestic sexual partnerships. With the increasing HIV incidence in Asia (the most common destination for UK travellers after sub-Saharan Africa), the number of cases of HIV contracted abroad may rise in the future.

Adult↗
PubMed1994

A sex comparison of rates of new AIDS-defining disease and death in 2554 AIDS cases. AIDS in Europe Study Group.

OBJECTIVES: To compare the development rate of new AIDS-defining diseases between 566 women and 1988 men with AIDS who were infected with HIV via the same routes (mainly by sharing drug injecting equipment and heterosexual sex). DESIGN: Information on patient follow-up after AIDS diagnosis was obtained by retrospectively reviewing case notes. METHODS: The 2554 men and women were followed from the time of AIDS diagnosis as part of the multicentre AIDS in Europe study, which examined AIDS cases diagnosed at 52 centres in 17 European countries between 1979 and 1989. Incidence of AIDS-defining diseases and demographic variables were recorded for all patients and CD4 lymphocyte count at the time of AIDS diagnosis for approximately half the patients. RESULTS: Only toxoplasmosis and herpes simplex virus ulceration showed statistically significant differences in occurrence rate between women and men [relative risks (RR), 1.51 and 3.44; 95% confidence interval (CI), 1.51 1.09-2.08 and 3.44 1.92-6.23, respectively] which remained after adjusting for imbalances in other variables. For both diseases, the additional absolute rate in women was approximately three per 100 person-years at risk. Survival after AIDS diagnosis was also similar between the two sexes (RR, 0.96; 95% CI, 0.86-1.08). CONCLUSION: There appears to be little difference between women and men in the clinical course of AIDS.

AIDS-Related Opportunistic Infections↗
PubMed1994

The spectrum of autosomal dominant polycystic kidney disease in children.

The natural history of autosomal dominant polycystic kidney disease (ADPKD) has not been well described in children, and it is not known whether a relationship exists between renal structural abnormalities and function in children as has been seen in adults. Therefore, 140 children from 67 ADPKD families were studied in a prospective study. Only 22 children came with a previous diagnosis of ADPKD. In 44% of all children, at least one cyst was found on ultrasound at a mean age of 8.7 yr. Of these, 60% were classified as having moderate disease on the basis of a total cyst number of 1 to 10 cysts, whereas 40% were considered to have severe disease with a total of more than 10 cysts. There was a significant relationship between the severity of the renal structural involvement and the frequency of flank and back pain, hypertension, and impaired renal concentrating capacity. However, GFR were not reduced in children with ADPKD and did not relate to structural severity. Thirty-nine children were seen for a follow-up visit 2 to 5 yr after the initial visit. No child had progressed from nonaffected to affected with ADPKD, but three of four children with only one cyst at the time of the initial study had progressed to bilateral cysts. Among the 22 ADPKD children who had a follow-up study, there was progression of the disease, reflected by an increase in cyst number and an increase in the frequency of pain and hypertension. However, GFR remained stable in all children.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Pregnancy outcome and its relationship to progression of renal failure in autosomal dominant polycystic kidney disease.

The effect of pregnancy on renal disease has not been defined in autosomal dominant polycystic kidney disease (ADPKD). Therefore, fetal and maternal complication rates in ADPKD women as compared with those in unaffected family members (NADPKD) were assessed. Two hundred thirty-five ADPKD and 108 NADPKD women with 605 and 244 pregnancies, respectively, were studied. Overall, fetal complication rates were similar between ADPKD and NADPKD women (32.6 versus 26.2%). Fetal complications were more common in ADPKD women when they were older than 30 yr. Increased fetal prematurity rates were found in preeclamptic ADPKD women as compared with normotensive ADPKD women (28 versus 10%; P < 0.01). More maternal complications occurred in ADPKD as compared with NADPKD women (35 versus 19%; P < 0.001), with preexisting hypertension being the most important risk factor for a maternal complication to occur. Normotensive ADPKD women who developed preeclampsia were more likely to develop chronic hypertension as compared with those without preeclampsia (89 versus 58%; P < 0.01). Hypertensive ADPKD women with four or more pregnancies had lower creatinine clearances than age-adjusted hypertensive ADPKD women with fewer than four pregnancies (49 +/- 5 versus 66 +/- 3 mL/min per 1.73 m2; P < 0.01). Therefore, normotensive ADPKD women usually have successful, uncomplicated pregnancies. However, hypertensive ADPKD women are at high risk for fetal and maternal complications and measures should be taken to prevent the development of preeclampsia in these women.

Adult↗
PubMed1994

Overt proteinuria and microalbuminuria in autosomal dominant polycystic kidney disease.

The amount of proteinuria is a prognostic indicator in a variety of glomerular disorders. To examine the importance of urinary protein excretion in autosomal dominant polycystic kidney disease, this study determined the clinical characteristics of autosomal dominant polycystic kidney disease patients with established proteinuria and the frequency of microalbuminuria in hypertensive autosomal dominant polycystic kidney disease patients without proteinuria. In 270 autosomal dominant polycystic kidney disease patients, mean 24-h urinary protein excretion was 259 +/- 22 mg/day. Forty-eight of 270 autosomal dominant poly-cystic kidney disease patients had over proteinuria (> 300 mg/day). The patients with established proteinuria had higher mean arterial pressures, larger renal volumes, and lower creatinine clearances than did their nonproteinuric counterparts (all P < 0.0001), a greater pack year smoking history (P < 0.05), and the projection of a more aggressive course of renal disease (P < 0.05). All autosomal dominant polycystic kidney disease patients with established proteinuria were hypertensive, as compared with 67% without established proteinuria (P < 0.001). Forty-nine patients with hypertension and left ventricular hypertrophy without established proteinuria were examined for microalbuminuria; 41% demonstrated microalbuminuria. Those with microalbuminuria had higher mean arterial pressure, larger renal volumes and increased filtration fraction. Therefore, established proteinuria and microalbuminuria in autosomal dominant polycystic kidney disease patients are associated with increased mean arterial pressure and more severe renal cystic involvement.

Adult↗
PubMed1994

Scientific hypothesis: a new strategy for the design of anti-protozoal drugs--DNA polymerase as a drug target.

Chemotherapy against protozoan diseases has been practised since ancient times. Although still widely used, antiparasitic drugs are seldom completely effective. Complete elimination of an extensive protozoan infection usually requires a combination of drugs which target parasitic mechanisms very similar to the human host, as manifested by a multitude of side effects of varying severity. Furthermore, there is an escalating problem of widespread resistance to commonly used chemotherapeutic agents. Here we present an alternative strategy for the design of antiprotozoal agents using the principal enzyme involved in DNA replication as a possible drug target--DNA polymerase.

Animals↗
PubMed1994

Species-specific identification of Sarcocystis and Toxoplasma by PCR amplification of small subunit ribosomal RNA gene fragments.

The small subunit (SSU) ribosomal RNA (rRNA) genes of four cyst-forming coccidia (Sarcocystis tenella, Sarcocystis arieticanis, Sarcocystis gigantea, Toxoplasma gondii) infecting sheep were analysed for unique target sequences which could be used as priming sites for species-specific polymerase chain reactions (PCR). A total of 11 putatively species-specific oligonucleotides were tested in combination with universal oligonucleotides designed for conserved regions of the SSU rRNA genes of eukaryotes. For each parasite species two of these oligonucleotide pairs were found to be ideal primers for species-specific amplification of SSU rRNA gene fragments. The specificity of the PCR assays was optimised by testing different PCR parameters (annealing temperature, magnesium ion concentration, number of amplification cycles) with genomic DNA preparations derived from S. tenella, S. arieticanis, S. gigantea, T. gondii and sheep. The new PCR assays are a powerful tool for species-specific differentiation of the three ovine Sarcocystis spp. and T. gondii.

Animals↗
PubMed1994

New international reference preparation for proteins in human serum (RPPHS).

Quality-control surveys in recent years, in various parts of the world, have shown poor between-laboratory agreement for measurements of plasma proteins. Despite the existence of international reference materials distributed by the World Health Organization, standards produced by diagnostics manufacturers and professional organizations differ significantly in their ascribed values. The reasons for this are complex but include poor availability of the primary materials, confusion about their use, and the fact that their turbidity on reconstitution precludes their use in modern optical immunoassays. This unfortunate situation led to an important initiative to produce sufficient quantities of a widely available, optically clear secondary reference material for plasma proteins that could be used worldwide by manufacturers, professional organizations, and laboratories. Here we present an overview on how the laboratory community, including manufacturers, clinical laboratories, professional societies, and regulators, has reached what we consider is a successful conclusion to a difficult problem.

Blood Proteins↗
PubMed1993

Analysis of dinucleotide frequency and codon usage in the phylum Apicomplexa.

Dinucleotide frequency (DiF) and codon usage (cu) were analysed in gene sequences from four parasitic protozoa, Babesia bovis, Theileria parva, Toxoplasma gondii and Eimeria tenella, of the phylum Apicomplexa. In keeping with the 'genome hypothesis', cu was found to be non-random and species specific in these organisms, although cu among members of the same subclass was found to be very similar. Several low-usage (lu) codons were identified, and the usage of lu codons appears to be related to the taxonomic position of the organisms under study. A comparison of the observed/expected DiF ratios obtained from gene coding regions revealed a low frequency of the TA and CG dinucleotides in all organisms studied. A comparison of these DiF ratios with those found in rRNA-encoding genes and in introns, showed that in the parasites, B. bovis and Th. parva (representing the piroplasms), the low frequency of dinucleotides appeared to be the result of coding pressure alone. In T. gondii and E. tenella (representing the coccidia), however, coding pressure could not completely explain differences in DiF.

Animals↗
PubMed1993

Sexual behaviour.

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Data Collection↗
PubMed1993

Further characterization of the respiratory deficient dum-1 mutation of Chlamydomonas reinhardtii and its use as a recipient for mitochondrial transformation.

The respiratory deficient dum-1 mutant of Chlamydomonas reinhardtii fails to grow in the dark because of a terminal 1.5 kb deletion in the linear 15.8 kb mitochondrial genome, which affects the apocytochrome b (CYB) gene. In contrast to the wild type where only mitochondrial genomes of monomer length are observed, the dum-1 genomes are present as a mixture of monomer and dimer length molecules. The mutant dimers appear to result from head-to-head fusions of two deleted molecules. Furthermore, mitochondrial genomes of dum-1 were also found to be unstable, with the extent of the deletion varying among single cell clones from the original mutant population. The dum-1 mutant also segregates, at a frequency of ca. 4% per generation, lethal minute colonies in which the original deletion now extends at least into the adjacent gene encoding subunit four of NAD dehydrogenase (ND4). We have used the dum-1 mutant as a recipient to demonstrate stable mitochondrial transformation in C. reinhardtii employing the biolistic method. After 4 to 8 weeks dark incubation, a total of 22 respiratory competent colonies were isolated from plates of dum-1 cells bombarded with C. reinhardtii mitochondrial DNA (frequency 7.3 x 10(-7)) and a single colony was isolated from plates bombarded with C. smithii mitochondrial DNA (frequency 0.8 x 10(-7)). No colonies were seen on control plates (frequency < 0.96 x 10(-9)). All transformants grew normally in the dark on acetate media; 22 transformants were homoplasmic for the wild-type mitochondrial genome typical of the C. reinhardtii donor. The single transformant obtained from the C. smithii donor had a recombinant mitochondrial genome containing the donor CYB gene and the diagnostic HpaI and XbaI restriction sites in the gene encoding subunit I of cytochrome oxidase (COI) from the C. reinhardtii recipient. The characteristic deletion fragments of the dum-1 recipient were not detected in any of the transformants.

Animals↗