Diagnostic accuracy of a prototype rapid chlamydia and gonorrhoea recombinase polymerase amplification assay: a multicentre cross-sectional preclinical evaluation

Objectives

Rapid and accurate sexually transmitted infection diagnosis can reduce onward transmission and improve treatment efficacy. We evaluated the accuracy of a 15-minute run-time recombinase polymerase amplification–based prototype point-of-care test (TwistDx) for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG).

Methods

Prospective, multicentre study of symptomatic and asymptomatic patients attending three English sexual health clinics. Research samples provided were additional self-collected vulvovaginal swab (SCVS) (female participants) and first-catch urine (FCU) aliquot (female and male participants). Samples were processed blind to the comparator (routine clinic CT/NG nucleic acid amplification test (NAAT)) results. Discrepancies were resolved using Cepheid CT/NG GeneXpert.

Results

Both recombinase polymerase amplification and routine clinic NAAT results were available for 392 male and 395 female participants. CT positivity was 8.9% (35/392) (male FCU), 7.3% (29/395) (female FCU) and 7.1% (28/395) (SCVS). Corresponding NG positivity was 3.1% (12/392), 0.8% (3/395) and 0.8% (3/395). Specificity and positive predictive values were 100% for all sample types and both organisms, except male CT FCU (99.7% specificity (95% confidence interval (CI) 98.4–100.0; 356/357), 97.1% positive predictive value (95% CI 84.7–99.9; 33/34)). For CT, sensitivity was ≥94.3% for FCU and SCVS. CT sensitivity for female FCU was higher (100%; 95% CI, 88.1–100; 29/29) than for SCVS (96.4%; 95% CI, 81.7–99.9; 27/28). NG sensitivity and negative predictive values were 100% in FCU (male and female).

Conclusions

This prototype test has excellent performance characteristics, comparable to currently used NAATs, and fulfils several World Health Organization ASSURED criteria. Its rapidity without loss of performance suggests that once further developed and commercialized, this test could positively affect clinical practice and public health.

Expanding CEP290 mutational spectrum in ciliopathies

Ciliopathies are an expanding group of rare conditions characterized by multiorgan involvement, that are caused by mutations in genes encoding for proteins of the primary cilium or its apparatus. Among these genes, CEP290 bears an intriguing allelic spectrum, being commonly mutated in Joubert syndrome and related disorders (JSRD), Meckel syndrome (MKS), Senior-Loken syndrome and isolated Leber congenital amaurosis (LCA). Although these conditions are recessively inherited, in a subset of patients only one CEP290 mutation could be detected. To assess whether genomic rearrangements involving the CEP290 gene could represent a possible mutational mechanism in these cases, exon dosage analysis on genomic DNA was performed in two groups of CEP290 heterozygous patients, including five JSRD/MKS cases and four LCA, respectively. In one JSRD patient, we identified a large heterozygous deletion encompassing CEP290 C-terminus that resulted in marked reduction of mRNA expression. No copy number alterations were identified in the remaining probands. The present work expands the CEP290 genotypic spectrum to include multiexon deletions. Although this mechanism does not appear to be frequent, screening for genomic rearrangements should be considered in patients in whom a single CEP290 mutated allele was identified.

Conditional expression of mutated K-ras accelerates intestinal tumorigenesis in Msh2-deficient mice

K-ras mutation occurs in 40-50% of human colorectal adenomas and carcinomas, but its contribution to intestinal tumorigenesis in vivo is unclear. We developed K-ras(V12) transgenic mice that were crossed with Ah-Cre mice to generate K-ras(V12)/Cre mice, which showed beta-naphthoflavone-induction of Cre-mediated LoxP recombination that activated intestinal expression of K-ras(V12) 4A and 4B transcripts and proteins. Only very occasional intestinal adenomas were observed in beta-naphthoflavone-treated K-ras(V12)/Cre mice aged up to 2 years, suggesting that mutated K-ras expression alone does not significantly initiate intestinal tumourigenesis. To investigate the effects of mutated K-ras on DNA mismatch repair (MMR)-deficient intestinal tumour formation, these mice were crossed with Msh2(-/-) mice to generate K-ras(V12)/Cre/Msh2(-/-) offspring. After beta-naphthoflavone treatment, K-ras(V12)/Cre/Msh2(-/-) mice showed reduced average lifespan of 17.3+/-5.0 weeks from 26.9+/-6.8 (control Msh2(-/-) mice) (P<0.01). They demonstrated increased adenomas in the small intestine from 1.41 (Msh2(-/-) controls) to 7.75 per mouse (increased fivefold, P<0.01). In the large intestine, very few adenomas were found in Msh2(-/-) mice (0.13 per mouse) whereas K-ras(V12)/Cre/Msh2(-/-) mice produced 2.70 adenomas per mouse (increased 20-fold, P<0.01). Over 80% adenomas from K-ras(V12)/Cre/Msh2(-/-) mice showed transgene recombination with expression of K-ras(V12) 4A and 4B transcripts and proteins. Sequencing of endogenous murine K-ras showed mutations in two out of 10 tumours examined from Msh2(-/-) mice, but no mutations in 17 tumours from K-ras(V12)/Cre/Msh2(-/-) mice. Expression of K-ras(V12) in tumours caused activation of the mitogen-activated protein kinase and Akt/protein kinase B signaling pathways, demonstrated by phosphorylation of p44MAPK, Akt and GSK3beta, as well as transcriptional upregulation of Pem, Tcl-1 and Trap1a genes (known targets of K-ras(V12) expression in stem cells). Thus, mutated K-ras cooperates synergistically with MMR deficiency to accelerate intestinal tumorigenesis, particularly in the large intestine.

Mutant K-ras enhances apoptosis in embryonic stem cells in combination with DNA damage and is associated with increased levels of p19(ARF)

The roles of K-ras in neoplasia are not entirely understood, although there is evidence that K-ras affects susceptibility to apoptosis, modulating survival of DNA damaged cells which would otherwise be eliminated. In this study, we investigated the effects of mutant K-ras on apoptosis in vitro following DNA damage. To avoid complications resulting from mutations in other cancer-related genes and from the presence of endogenous K-ras, we derived K-ras null embryonic stem cells. Expression of either wild-type or mutant K-ras was reconstructed by stable plasmid transfection. The cell lines were treated with etoposide, cisplatin and UV radiation and apoptosis measured flow cytometrically. Mutant K-ras potentiated the effect of etoposide-derived DNA damage by increasing apoptosis, whereas absence of K-ras had the opposite effect. This pattern was similar but less marked with cisplatin, whereas UV yielded no difference in apoptosis with regard to K-ras status, suggesting that the effect of K-ras on apoptosis is dependent on the nature of the DNA damage. To investigate possible mechanisms, we examined the expression of p19(ARF) mRNA by RT-PCR. Cells expressing mutant K-ras produced elevated levels of p19(ARF) mRNA, which could link K-ras status with p53 expression and hence susceptibility to DNA damage-induced apoptosis.

Generation of HIV latency during thymopoiesis

The use of combination antiretroviral therapy results in a substantial reduction in viremia, a rebound of CD4+ T cells and increased survival for HIV-infected individuals. However, this treatment does not result in the total eradication of HIV. Rather, the virus is thought to remain latent in a subset of cells, where it avoids elimination by the immune system. In this state the virus is capable of reactivation of productive infection following cessation of therapy. These latently infected cells are very few in number and it has thus been difficult to determine their origin and to study the molecular nature of the latent viral genome. HIV replication is linked to cellular gene transcription and requires target cell activation. Therefore, should an activated, infected cell become transcriptionally inactive prior to cytopathic effects, the viral genome might be maintained in a latent state. We used the SCID-hu (Thy/Liv) mouse model to establish that activation-inducible HIV can be generated at high frequency during thymopoiesis, a process where previously activated cells mature towards quiescence. Moreover, we showed that these cells can be exported into the periphery where the virus remains latent until T-cell receptor stimulation, indicating that the thymus might be a source of latent HIV in humans.

In vivo evidence of brain galactitol accumulation in an infant with galactosemia and encephalopathy

In a newborn infant with galactose-1-phosphate uridyltransferase deficiency and encephalopathy, brain magnetic resonance imaging revealed cytotoxic edema in white matter. Using in vivo proton magnetic resonance spectroscopy, we detected approximately 8 mmol galactitol per kilogram of brain tissue, an amount potentially relevant to the pathogenesis of brain edema.

Increased serum transferrin receptor concentrations in Friedreich ataxia

Mitochondrial iron accumulation is thought to underlie the pathophysiology of Friedreich ataxia and may occur at the expense of cytosolic iron. Decreases in cytosolic iron induce expression of the transferrin receptor, some of which is released into the serum. Here, we demonstrate that serum transferrin receptor concentrations are increased in patients with Friedreich ataxia, which supports the hypothesis that it is a disease of abnormal intracellular iron distribution.

Human immunodeficiency virus type 1-induced hematopoietic inhibition is independent of productive infection of progenitor cells in vivo

Human immunodeficiency virus (HIV)-infected individuals exhibit a variety of hematopoietic dysfunctions. The SCID-hu mouse (severe combined immunodeficient mouse transplanted with human fetal thymus and liver tissues) can be used to model the loss of human hematopoietic precursor cell function following HIV infection and has a distinct advantage in that data can be obtained in the absence of confounding factors often seen in infected humans. In this study, we establish that HIV type 1 (HIV-1) bearing a reporter gene inserted into the viral vpr gene is highly aggressive in depleting human myeloid and erythroid colony-forming precursor activity in vivo. Human CD34(+) progenitor cells can be efficiently recovered from infected implants yet do not express the viral reporter gene, despite severe functional defects. Our results indicate that HIV-1 infection alone leads to hematopoietic inhibition in vivo; however, this effect is due to indirect mechanisms rather than to direct infection of CD34(+) cells in vivo.

Canine necrotizing sialometaplasia: a case report and review of the literature

Necrotizing sialometaplasia (NS) is a distinct, though rare disease of the salivary glands. Histologic findings in humans and dogs are identical, but the distribution of affected glands and clinical course are very different. Small terrier breeds are predisposed. Clinically, canine NS is characterized by nausea (i.e., ptyalism, lip smacking, gulping), dysphagia, and pain in the mandibular region. Surgical removal of the affected glands produces minimal, if any, improvement; however, transient administration of anticonvulsants has resulted in dramatic clinical improvement in three cases.

Myelin protein zero gene mutated in Charcot-Marie-tooth type 1B patients

Autosomal dominant of Charcot-Marie-Tooth disease (CMT), whose gene is type 1B (CMT1B), has slow nerve conduction with demyelinated Schwann cells. In this study the abundant peripheral myelin protein zero (MPZ) gene, MPZ, was mapped 130 kb centromeric to the Fc receptor immunoglobulin gene cluster in band 1q22, and a major MPZ point mutation was found to cosegregate with CMT1B in one large CMT1B family. The MPZ point mutation in 18 of 18 related CMT1B pedigree 1 patients converts a positively charged lysine in codon 96 to a negatively charged glutamate. The same MPZ locus cosegregates with the CMT1B disease gene in a second CMT1B family [total multipoint logarithm of odds (lod) = 11.4 at theta = 0.00] with a splice junction mutation. Both mutations occur in MPZ protein regions otherwise conserved identically in human, rat, and cow since these species diverged 100 million years ago. MPZ protein, expressed exclusively in myelinated peripheral nerve Schwann cells, constitutes > 50% of myelin protein. These mutations are anticipated to disrupt homophilic MPZ binding and result in CMT1B peripheral nerve demyelination.

Structure and expression of human IgG FcRII(CD32). Functional heterogeneity is encoded by the alternatively spliced products of multiple genes

The structural heterogeneity of the human low affinity receptor for IgG, FcRII(CD32), has been elucidated through the isolation, characterization, and expression of cDNA clones derived from myeloid and lymphoid RNA. These clones predict amino acid sequences consistent with integral membrane glycoproteins with single membrane spanning domains. The extracellular domains display sequence homology to other Fc gamma Rs and members of the Ig supergene family. A minimum of three genes (Fc gamma RIIa, IIa', and Fc gamma RIIb) encode these transcripts, which demonstrate highly related extracellular and membrane spanning domains. IIa/IIa' differ substantially in the intracytoplasmic domain from IIb. Alternative splicing of the IIb gene generates further heterogeneity in both NH2- and COOH-terminal domains of the predicted proteins. Comparison to the murine homologues of these molecules reveals a high degree of conservation between the products of one of these genes, Fc gamma RIIb, and the murine beta gene in primary sequence, splicing pattern, and tissue distribution. In contrast, the sequence of IIa' indicates its relationship to the beta-like genes, with mutation giving rise to a novel cytoplasmic domain, while IIa is a chimera of both alpha- and beta-like genes. Expression of these cDNA molecules by transfection results in the appearance of IgG binding molecules that bear the epitopes defined by the FcRII(CD32) mAbs previously described.