Rates of referable eye disease in the Scottish National Diabetic Retinopathy Screening Programme.

AIMS: Diabetic retinopathy screening aims to detect people at risk of visual loss due to proliferative diabetic retinopathy, but also refers cases of suspected macular oedema (maculopathy). At the introduction of screening, ophthalmology was concerned that referral rates would be unmanageable. We report yield of referable disease by referral reason for the first 5 years of the programme. METHODS: We extracted screening results from a nationwide clinical diabetes database to calculate annual referral rates to ophthalmic clinics. We used logistic regression to examine associations between clinical measures and referable disease. RESULTS: 182 397 people underwent ≥ 1successful retinal screening between 2006 and 2010. The yield of referable eye disease was highest in the first 2 years of screening (7.0% and 6.0%) before stabilising at ∼4.3%. The majority of referrals are due to maculopathy with 73% of referrals in 2010 based on a finding of maculopathy. CONCLUSIONS: The commonest cause for referral is for suspected macular oedema (maculopathy). Referral rates for retinopathy have stabilised, as predicted, at relatively low rates. However, ophthalmology workload continues to rise as new treatment options (ie, monthly intraocular injections) have unexpectedly increased the impact on ophthalmology. A review of the screening referral path for maculopathy may be timely.

Predicted impact of extending the screening interval for diabetic retinopathy: the Scottish Diabetic Retinopathy Screening programme.

AIMS/HYPOTHESIS: The aim of our study was to identify subgroups of patients attending the Scottish Diabetic Retinopathy Screening (DRS) programme who might safely move from annual to two yearly retinopathy screening. METHODS: This was a retrospective cohort study of screening data from the DRS programme collected between 2005 and 2011 for people aged ≥12 years with type 1 or type 2 diabetes in Scotland. We used hidden Markov models to calculate the probabilities of transitions to referable diabetic retinopathy (referable background or proliferative retinopathy) or referable maculopathy. RESULTS: The study included 155,114 individuals with no referable diabetic retinopathy or maculopathy at their first DRS examination and with one or more further DRS examinations. There were 11,275 incident cases of referable diabetic eye disease (9,204 referable maculopathy, 2,071 referable background or proliferative retinopathy). The observed transitions to referable background or proliferative retinopathy were lower for people with no visible retinopathy vs mild background retinopathy at their prior examination (respectively, 1.2% vs 8.1% for type 1 diabetes and 0.6% vs 5.1% for type 2 diabetes). The lowest probability for transitioning to referable background or proliferative retinopathy was among people with two consecutive screens showing no visible retinopathy, where the probability was <0.3% for type 1 and <0.2% for type 2 diabetes at 2 years. CONCLUSIONS/INTERPRETATION: Transition rates to referable diabetic eye disease were lowest among people with type 2 diabetes and two consecutive screens showing no visible retinopathy. If such people had been offered two yearly screening the DRS service would have needed to screen 40% fewer people in 2009.

Membrane traffic: how do GGAs fit in with the adaptors?

The AP-1 adaptor complex has been cast as the major player in clathrin coat formation for vesicular transport from the trans-Golgi to the endocytic pathway. But new results on 'GGA' proteins have raised doubts about this paradigm and suggest both a new sorting mechanism and an unexpected complexity in the roles of clathrin.

Ionophore-resistant mutants of Toxoplasma gondii reveal host cell permeabilization as an early event in egress.

Toxoplasma gondii is an obligate intracellular pathogen within the phylum Apicomplexa. Invasion and egress by this protozoan parasite are rapid events that are dependent upon parasite motility and appear to be directed by fluctuations in intracellular [Ca(2+)]. Treatment of infected host cells with the calcium ionophore A23187 causes the parasites to undergo rapid egress in a process termed ionophore-induced egress (IIE). In contrast, when extracellular parasites are exposed to this ionophore, they quickly lose infectivity (termed ionophore-induced death [IID]). From among several Iie(-) mutants described here, two were identified that differ in several attributes, most notably in their resistance to IID. The association between the Iie(-) and Iid(-) phenotypes is supported by the observation that two-thirds of mutants selected as Iid(-) are also Iie(-). Characterization of three distinct classes of IIE and IID mutants revealed that the Iie(-) phenotype is due to a defect in a parasite-dependent activity that normally causes infected host cells to be permeabilized just prior to egress. Iie(-) parasites underwent rapid egress when infected cells were artificially permeabilized by a mild saponin treatment, confirming that this step is deficient in the Iie(-) mutants. A model is proposed that includes host cell permeabilization as a critical part of the signaling pathway leading to parasite egress. The fact that Iie(-) mutants are also defective in early stages of the lytic cycle indicates some commonality between these normal processes and IIE.

Polar transmembrane domains target proteins to the interior of the yeast vacuole.

Membrane proteins transported to the yeast vacuole can have two fates. Some reach the outer vacuolar membrane, whereas others enter internal vesicles, which form in late endosomes, and are ultimately degraded. The vacuolar SNAREs Nyv1p and Vam3p avoid this fate by using the AP-3-dependent pathway, which bypasses late endosomes, but the endosomal SNARE Pep12p must avoid it more directly. Deletion analysis revealed no cytoplasmic sequences necessary to prevent the internalization of Pep12p in endosomes. However, introduction of acidic residues into the cytoplasmic half of the transmembrane domain created a dominant internalization signal. In other contexts, this same feature diverted proteins from the Golgi to endosomes and slowed their exit from the endoplasmic reticulum. The more modestly polar transmembrane domains of Sec12p and Ufe1p, which normally serve to hold these proteins in the endoplasmic reticulum, also cause Pep12p to be internalized, as does that of the vacuolar protein Cps1p. It seems that quality control mechanisms recognize polar transmembrane domains at multiple points in the secretory and endocytic pathways and in endosomes sort proteins for subsequent destruction in the vacuole. These mechanisms may minimize the damaging effects of abnormally exposed polar residues while being exploited for the localization of some normal proteins.

A selective transport route from Golgi to late endosomes that requires the yeast GGA proteins.

Pep12p is a yeast syntaxin located primarily in late endosomes. Using mutagenesis of a green fluorescent protein chimera we have identified a sorting signal FSDSPEF, which is required for transport of Pep12p from the exocytic pathway to late endosomes, from which it can, when overexpressed, reach the vacuole. When this signal is mutated, Pep12p instead passes to early endosomes, a step that is determined by its transmembrane domain. Surprisingly, Pep12p is then specifically retained in early endosomes and does not go on to late endosomes. By testing appropriate chimeras in mutant strains, we found that FSDSPEF-dependent sorting was abolished in strains lacking Gga1p and Gga2p, Golgi-associated coat proteins with homology to gamma adaptin. In the gga1 gga2 double mutant endogenous Pep12p cofractionated with the early endosome marker Tlg1p, and recycling of Snc1p through early endosomes was defective. Pep12p sorting was also defective in cells lacking the clathrin heavy or light chain. We suggest that specific and direct delivery of proteins to early and late endosomes is required to maintain the functional heterogeneity of the endocytic pathway and that the GGA proteins, probably in association with clathrin, help create vesicles destined for late endosomes.

Lytic cycle of Toxoplasma gondii.

Toxoplasma gondii is an obligate intracellular pathogen within the phylum Apicomplexa. This protozoan parasite is one of the most widespread, with a broad host range including many birds and mammals and a geographic range that is nearly worldwide. While infection of healthy adults is usually relatively mild, serious disease can result in utero or when the host is immunocompromised. This sophisticated eukaryote has many specialized features that make it well suited to its intracellular lifestyle. In this review, we describe the current knowledge of how the asexual tachyzoite stage of Toxoplasma attaches to, invades, replicates in, and exits the host cell. Since this process is closely analogous to the way in which viruses reproduce, we refer to it as the Toxoplasma "lytic cycle."

Development of a stable episomal shuttle vector for Toxoplasma gondii.

The rapid developments in the molecular genetics of Toxoplasma gondii have far reaching implications in treatment and vaccination strategies for this as well as closely related pathogens such as Plasmodium. Although stable transformation of this parasite through homologous and illegitimate genomic integration has provided many of the tools necessary for genetic analysis, subsequent manipulations of the DNA have proven laborious. This report describes the selection and subsequent characterization of a Toxoplasma sequence that permits the episomal maintenance of bacterial plasmids in this parasite. This sequence was isolated from the Toxoplasma genome through selection for episomal stability of a pUC19-based library in the absence of a selectable marker. A 500-base pair fragment was determined to possess the stabilization activity. Transformations of Toxoplasma using vectors possessing this fragment, referred to as EMS (episomal maintenance sequence), demonstrated an elevated stable transformation frequency compared with the vector alone. Mutants deficient in hypoxanthine-xanthine-guanine phosphoribosyltransferase activity were used as a test to see if this gene could be selected from a genomic library using a vector containing the EMS. The success of this test demonstrates the utility of EMS-containing vectors in complementation strategies and the ability of such constructs bearing large fragments of the Toxoplasma genome to be maintained episomally.

Semi-automated method for the determination of free fatty acids in plasma.

A semi-automated method for the determination of free fatty acids in plasma based on Mosinger's manual method (Mosinger, 1965) is described and the results of a comparison with Dole's titrimetric method (Dole, 1956) are presented. There is almost perfect correlation between the two methods, and the automated technique is simple, reliable, and significantly more accurate and precise than the titrimetric method.