Trophoblast glycoprotein is required for efficient synaptic vesicle exocytosis from retinal rod bipolar cells

Introduction

Rod bipolar cells (RBCs) faithfully transmit light-driven signals from rod photoreceptors in the outer retina to third order neurons in the inner retina. Recently, significant work has focused on the role of leucine-rich repeat (LRR) proteins in synaptic development and signal transduction at RBC synapses. We previously identified trophoblast glycoprotein (TPBG) as a novel transmembrane LRR protein localized to the dendrites and axon terminals of RBCs.

Methods

We examined the effects on RBC physiology and retinal processing of TPBG genetic knockout in mice using immunofluorescence and electron microscopy, electroretinogram recording, patch-clamp electrophysiology, and time-resolved membrane capacitance measurements.

Results

The scotopic electroretinogram showed a modest increase in the b-wave and a marked attenuation in oscillatory potentials in the TPBG knockout. No effect of TPBG knockout was observed on the RBC dendritic morphology, TRPM1 currents, or RBC excitability. Because scotopic oscillatory potentials primarily reflect RBC-driven rhythmic activity of the inner retina, we investigated the contribution of TPBG to downstream transmission from RBCs to third-order neurons. Using electron microscopy, we found shorter synaptic ribbons in TPBG knockout axon terminals in RBCs. Time-resolved capacitance measurements indicated that TPBG knockout reduces synaptic vesicle exocytosis and subsequent GABAergic reciprocal feedback without altering voltage-gated Ca2+ currents.

Discussion

TPBG is required for normal synaptic ribbon development and efficient neurotransmitter release from RBCs to downstream cells. Our results highlight a novel synaptic role for TPBG at RBC ribbon synapses and support further examination into the mechanisms by which TPBG regulates RBC physiology and circuit function.

Ocular Morpho-Functional Evaluation in ATTRv Pre-Symptomatic Carriers: A Case Series

The present study aimed to investigate ocular findings in hereditary transthyretin amyloidosis (ATTRv) pre-symptomatic carriers. Fourteen ATTRv pre-symptomatic carriers, who are patients with positive genetic testing but without signs or symptoms of the disease, were retrospectively evaluated. Retinal morphology was assessed using optical coherence tomography (OCT) and OCT-angiography. Retinal function was evaluated using cone b-wave and photopic negative response (PhNR). Pupillometry and in vivo corneal confocal microscopy (IVCM) were performed. ATTRv pre-symptomatic carriers presented a significantly reduced central macular thickness (CMT) (p = 0.01) and outer nuclear layer (ONL) thickness (p = 0.01) in comparison to normal controls. No differences were found when analyzing sub-foveal choroidal thickness, retinal nerve fiber layer and ganglion cell complex. In comparison to healthy controls, pre-symptomatic carriers presented an attenuated superficial retinal vascular network and a significantly augmented PhNR amplitude (p = 0.01). However, PhNR implicit times, B-wave amplitude and B-wave peak time did not show significant differences in comparison to controls. No differences were found for pupillometric values. All the examined eyes presented alterations in the IVCM. Preclinical ocular structural and functional abnormalities can be found in ATTRv pre-symptomatic carriers. Thus, an extensive ophthalmological evaluation should be included at the baseline visit and during follow-up. Considering the availability of new drugs potentially able to prevent or delay disease progression, the identification of new disease biomarkers appears to be particularly promising.

Luminance white noise electroretinograms (wnERGs) in mice

Purpose

To record and analyse electroretinograms (ERGs) to luminance stimuli with white noise temporal profiles in mice. White noise stimuli are expected to keep the retina in a physiologically more natural state than, e.g., flashes. The influence of mean luminance (ML) was studied.

Methods

Electroretinograms to luminance temporal white noise (TWN) modulation (wnERGs) were measured. The white noise stimuli contained all frequencies up to 20 Hz with equal amplitudes and random phases. Responses were recorded at 7 MLs between -0.7 and 1.2 log cd/m². Impulse response functions (IRFs) were calculated by cross correlating the averaged white noise electroretinogram (wnERG) responses with the stimulus. Amplitudes and latencies of the initial trough and subsequent peak in the IRFs were measured at each ML. Fourier transforms of the IRFs resulted in modulation transfer functions (MTFs). wnERGs were averaged across different animals. They were measured twice and the responses at identical instances in the 1st and 2nd recordings were plotted against each other. The correlation coefficient (r ² _repr) of the linear regression quantified the reproducibility. The results of the first and second measurement were further averaged. To study the underlying ERG mechanisms, the ERG potentials at the different MLs were plotted against those at the lowest and highest ML. The correlation coefficients (r ² _ML) were used to quantify their similarities.

Results

The amplitudes of the initial (a-wave-like) trough of the IRFs increased with increasing ML. The following positive (b-wave-like) peak showed a minimum at -0.4 log cd/m² above which there was a positive correlation between amplitude and ML. Their latencies decreased monotonously with increasing ML. In none of the IRFs, oscillatory potential (OP)-like components were observed. r ² _repr values were minimal at a ML of -0.1 log cd/m², where the MTFs changed from low-pass to band-pass. r ² _ML values increased and decreased with increasing ML when correlated with responses obtained at the highest or the lowest ML, respectively.

Conclusion

White noise electroretinograms can be reliably recorded in mice with luminance stimuli. IRFs resemble flash ERGs superficially, but they offer a novel procedure to study retinal physiology. New components can be described in the IRFs. The wnERGs are either rod- or cone-driven with little overlap.

Review: Use of Electrophysiological Techniques to Study Visual Functions of Aquatic Organisms

The light environments of natural water sources have specific characteristics. For the majority of aquatic organisms, vision is crucial for predation, hiding from predators, communicating information, and reproduction. Electroretinography (ERG) is a diagnostic method used for assessing visual function. An electroretinogram records the comprehensive potential response of retinal cells under light stimuli and divides it into several components. Unique wave components are derived from different retinal cells, thus retinal function can be determined by analyzing these components. This review provides an overview of the milestones of ERG technology, describing how ERG is used to study visual sensitivity (e.g., spectral sensitivity, luminous sensitivity, and temporal resolution) of fish, crustaceans, mollusks, and other aquatic organisms (seals, sea lions, sea turtles, horseshoe crabs, and jellyfish). In addition, it describes the correlations between visual sensitivity and habitat, the variation of visual sensitivity as a function of individual growth, and the diel cycle changes of visual sensitivity. Efforts to identify the visual sensitivity of different aquatic organisms are vital to understanding the environmental plasticity of biological evolution and for directing aquaculture, marine fishery, and ecosystem management.

Comparison of Machine Learning Approaches to Improve Diagnosis of Optic Neuropathy Using Photopic Negative Response Measured Using a Handheld Device

The photopic negative response of the full-field electroretinogram (ERG) is reduced in optic neuropathies. However, technical requirements for measurement and poor classification performance have limited widespread clinical application. Recent advances in hardware facilitate efficient clinic-based recording of the full-field ERG. Time series classification, a machine learning approach, may improve classification by using the entire ERG waveform as the input. In this study, full-field ERGs were recorded in 217 eyes (109 optic neuropathy and 108 controls) of 155 subjects. User-defined ERG features including photopic negative response were reduced in optic neuropathy eyes (p < 0.0005, generalized estimating equation models accounting for age). However, classification of optic neuropathy based on user-defined features was only fair with receiver operating characteristic area under the curve ranging between 0.62 and 0.68 and F1 score at the optimal cutoff ranging between 0.30 and 0.33. In comparison, machine learning classifiers using a variety of time series analysis approaches had F1 scores of 0.58–0.76 on a test data set. Time series classifications are promising for improving optic neuropathy diagnosis using ERG waveforms. Larger sample sizes will be important to refine the models.

Sex-Specific Retinal Anomalies Induced by Chronic Social Defeat Stress in Mice

Major depressive disorder (MDD) is one of the most common consequences of chronic stress. Still, there is currently no reliable biomarker to detect individuals at risk to develop the disease. Recently, the retina emerged as an effective way to investigate psychiatric disorders using the electroretinogram (ERG). In this study, cone and rod ERGs were performed in male and female C57BL/6 mice before and after chronic social defeat stress (CSDS). Mice were then divided as susceptible or resilient to stress. Our results suggest that CSDS reduces the amplitude of both oscillatory potentials and a-waves in the rods of resilient but not susceptible males. Similar effects were revealed following the analysis of the cone b-waves, which were faster after CSDS in resilient mice specifically. In females, rod ERGs revealed age-related changes with no change in cone ERGs. Finally, our analysis suggests that baseline ERG can predict with an efficacy up to 71% the expression of susceptibility and resilience before stress exposition in males and females. Overall, our findings suggest that retinal activity is a valid biomarker of stress response that could potentially serve as a tool to predict whether males and females will become susceptible or resilient when facing CSDS.

Ocular Involvement in Hereditary Transthyretin Amyloidosis: A Case Series Describing Novel Potential Biomarkers

Hereditary transthyretin amyloidosis (hATTR) is a rare disease caused by a point mutation in the transthyretin (TTR) gene and inherited in an autosomal dominant fashion. TTR is a plasma protein that functions as a carrier for thyroxine (T4) and retinol (vitamin A). Ophthalmological manifestations are due to both the hepatic and ocular production of mutated TTR. In this case series, we report the ocular manifestations of hATTR in eighteen eyes of nine consecutive patients. Corneal nerve abnormalities as well as morphological and functional changes in the retina were investigated. The study was a single-center, retrospective, observational, clinical case series. In all patients, corneal confocal microscopy (CCM), multimodal imaging of the retina, including fundus photography and Optical Coherence Tomography (OCT), as well as rod and cone electroretinography (ERG) were performed. Eight patients had active disease and one was an unaffected carrier. In all study eyes, corneal nerve plexa examined with CCM were poorly represented or absent. Mixed rod-cone and cone ERG b-wave amplitudes were reduced, and photopic b-wave responses were significantly delayed. Photopic Negative Response (PhNR) amplitude was significantly reduced, while PhNR latency was significantly augmented. In 13/18 eyes, vitreous opacities and abnormalities of vitreo-retinal interface were found. The current results highlight the presence of corneal nerve damage. Functional retinal abnormalities, detected by ERG, can be found even in the presence of minimal or absent structural retinal damage. These findings support the use of CCM and ERGs to detect early biomarkers for primary hATTR.

Comparison of the Humphrey Field Analyzer and Photopic Negative Response of Focal Macular Electroretinograms in the Evaluation of the Relationship Between Macula Structure and Function

Purpose: To investigate the association between macular inner retinal layer thickness and macula visual field (VF) mean deviation as measured by the Humphrey Field Analyzer (HFA) or macular function as measured by focal macular electroretinograms (ERGs) in patients with glaucoma.

Methods: The participants in this cross-sectional study were 71 patients with glaucoma and 10 healthy controls. Macular inner retinal layer thickness and function were measured in all participants using optical coherence tomography (OCT) and HFA or focal macular ERGs, respectively. Macular OCT images were segmented into the macular retinal nerve fiber layer (mRNFL), macular ganglion cell layer/inner plexiform layer (GCL/IPL), and ganglion cell complex (GCC). Spearman correlation analysis was used to assess the relationship between macular inner retinal layer thickness and function.

Results: Focal macular ERGs were composed of a negative wave (N1), a positive wave (P1), and a slow negative wave (N2). The N2 response density was significantly reduced in eyes with glaucoma, and was significantly associated with the thickness of the mRNFL (R = 0.317), GCL/IPL (R = 0.372), or GCC (R = 0.367). The observed structure–function relationship was also significantly correlated with the HFA VF mean deviation for each thickness [mRNFL (R = 0.728), GCL/IPL (R = 0.603), or GCC (R = 0.754)].

Conclusions: Although a significant correlation was found between the N2 response density and the thickness of the macular inner layer, the observed structure–function relationship with the mean deviation of the HFA VF was higher than that of the N2 response density.

Transient Increase and Delay of Multifocal Electroretinograms Following Laser Photocoagulations for Diabetic Macular Edema

Background: The acute physiological changes induced by focal retinal photocoagulation (PC) have been largely unexplored. Methods: This was a case-series study. We recorded multifocal electroretinograms (mfERGs) just before PC, and mfERGs were also recorded 5′, 15′, one hour, 24 h, and one week after the PCs. Transient changes of mfERGs were analyzed in eyes which underwent PCs to treat diabetic macular edema. The mfERGs recorded from the predominantly irradiated area and that from non-irradiated areas were analyzed separately. Results: Fifteen eyes of 15 patients were included in this study. The mfERGs elicited from non-irradiated areas did not change after PC, but the mfERGs elicited from the irradiated area changed with time; the amplitude was larger at 60′ than that before (p < 0.05) and at 5′ after PC (p < 0.01) and significantly smaller at 24 h and 1 week than that before and at 60′ after the PC (p < 0.01). The implicit time was significantly prolonged after PC. mfERG on irradiated area with the severe diabetic change was less altered after PCs. Conclusions: The transient increase in the amplitude at 60′ likely resulted from a biological amplification of partially damaged cells adjacent to the PC spots. The mfERGs manifested the dynamic alterations of the retinal function following PCs.

Retinal correlates of psychiatric disorders

Diagnosis and monitoring of psychiatric disorders rely heavily on subjective self-reports of clinical symptoms, which are complicated by the varying consistency of accounts reported by patients with an impaired mental state. Hence, more objective and quantifiable measures have been sought to provide clinicians with more robust methods to evaluate symptomology and track progression of disease in response to treatments. Owing to the shared origins of the retina and the brain, it has been suggested that changes in the retina may correlate with structural and functional changes in the brain. Vast improvements in retinal imaging, namely optical coherence tomography (OCT) and electrodiagnostic technology, have made it possible to investigate the eye at a microscopic level, allowing for the investigation of potential biomarkers in vivo. This review provides a summary of retinal biomarkers associated with schizophrenia, bipolar disorder and major depression, demonstrating how retinal biomarkers may be used to complement existing methods and provide structural markers of pathophysiological mechanisms that underpin brain dysfunction in psychiatric disorders.

Taurine Protects Retinal Cells and Improves Synaptic Connections in Early Diabetic Rats

Purpose: Taurine has long been thought to be involved in retinal protection from retinal degenerative diseases, but the underlying molecular mechanisms remain unclear. Retinal neurodegeneration is an early event in the pathogenesis of diabetic retinopathy (DR) that precedes and participates in the microcirculatory abnormalities that occur in DR. Our objective was to investigate the role and mechanisms of taurine in early diabetic retinas.Methods: Eight-week-old STZ-induced diabetic rats and control animals were randomly assigned to receive taurine or vehicle by intraperitoneal injection or by intragastric administration. The retinal function and retinal cell counts were evaluated using an electroretinography (ERG) and immunofluorescence microscopy. Plasma amino acids were measured by ion-exchange chromatography (IEC). The expression levels of retinal taurine transporter (Tau-T), mitochondria-dependent apoptosis-associated genes and reactive gliosis markers were studied by western blotting and immunofluorescence. Pre- and post-synaptic markers (PSD95 and mGluR6) in outer plexiform layer (OPL), and the bipolar cell marker protein kinase C alpha (PKCα) were localized by immunofluorescence. Levels of PSD95 and mGluR6 were determined by quantitative western blot.Results: Taurine significantly prevented the reduction of photopic b-wave amplitude and retinal cone cells and ganglion cells loss and maintained the Bcl-2/Bax ratio balance in diabetic rats. Taurine also prevented the upregulation of glial fibrillary acidic protein (GFAP) and reduced retinal reactive gliosis. Taurine reduced plasma glutamate and tyrosine levels, which were elevated in diabetic rats. Moreover, mGluR6 levels reduction detected by western blot and immunofluorescence in diabetic retinas was inhibited and the displacement of mGluR6 in OPL into the inner nuclear layer (INL) detected by immunofluorescence was reduced by Taurine treatment.Conclusion: Taurine may protect retinal cells from diabetic attacks by activating Tau-T, reducing retinal reactive gliosis, improving retinal synaptic connections and decreasing retinal cell apoptosis. Thus, taurine treatment may be a novel approach for early DR.

Visual Function in Mice Lacking GM3 Synthase

Purpose: Most complex gangliosides in vertebrates are formed from ganglioside GM3. GM3 deficiency in humans can result in epilepsy and visual impairment. To investigate whether a deficiency of GM3 is involved in visual function, ST3GAL5^-/- mice with mutations in the ST3GAL5 gene-coded GM3 synthase were employed. Materials and Methods: Sixty mice were employed in this study. The glycosphingolipids of mice retinas were analyzed through high performance thin layer chromatography. The morphology of the optic nerves and retinas were evaluated by hematoxylin and eosin staining and immunohistochemical analysis using an anti-glial fibrillary acidic protein (GFAP) antibody. An electroretinogram (ERG) was applied on the eyes of 4, 9, 12, and 14-month-old mice. Also, visual evoked potential (VEP) was applied on 13-month-old mice. Results: The GM3 in the retinas was detected in ST3GAL5^+/+ mice but not ST3GAL5^-/- mice. Also, GM1b and GD1α expressions and lactosylceramide accumulation were found in the ST3GAL5^-/- mouse retinas. There was no significant difference in GFAP expression in the retinas or optic discs between ST3GAL5^+/+ and ST3GAL5^-/- mice. Furthermore, the outcome of ERG and VEP analysis showed no disparity between the two strains in 13 and 14-month-old mice. Conclusion: In the eye, neither histopathological abnormalities nor abnormal functions of the retina were found in GM3-deficient mice. Differing from the situation in patients with GM3 deficiency, the lack of GM3 in mice did not lead to optic nerve atrophy.

Maintenance of Rhodopsin levels in Drosophila photoreceptor and phototransduction requires Protein Kinase D

During Drosophila phototransduction, the G protein coupled receptor (GPCR) Rhodopsin (Rh1) transduces photon absorption into electrical signal via G-protein coupled activation of phospholipase C (PLC). Rh1 levels in the plasma membrane are critical for normal sensitivity to light. In this study, we report that Protein Kinase D (dPKD) regulates Rh1 homeostasis in adult photoreceptors. Although eye development and retinal structure are unaffected in the dPKD hypomorph (dPKD^H), it exhibited elevated levels of Rh1. Surprisingly, despite having elevated levels of Rh1, no defect was observed in the electrical response to light in these flies. By contrast the levels of another transmembrane protein of the photoreceptor plasma membrane, Transient receptor potential (TRP) was not altered in dPKD^H. Our results indicate that dPKD is dispensable for eye development but is required for maintaining Rh1 levels in adult photoreceptors.

A Temporal White Noise Analysis for Extracting the Impulse Response Function of the Human Electroretinogram

PURPOSE

We introduce a method for determining the impulse response function (IRF) of the ERG derived from responses to temporal white noise (TWN) stimuli.

METHODS

This white noise ERG (wnERG) was recorded in participants with normal trichromatic vision to full-field (Ganzfeld) and 39.3° diameter focal stimuli at mesopic and photopic mean luminances and at different TWN contrasts. The IRF was obtained by cross-correlating the TWN stimulus with the wnERG.

RESULTS

We show that wnERG recordings are highly repeatable, with good signal-to-noise ratio, and do not lead to blink artifacts. The wnERG resembles a flash ERG waveform with an initial negativity (N1) followed by a positivity (P1), with amplitudes that are linearly related to stimulus contrast. These N1 and N1-P1 components showed commonalties in implicit times with the a- and b-waves of flash ERGs. There was a clear transition from rod- to cone-driven wnERGs at ∼1 photopic cd.m-2. We infer that oscillatory potentials found with the flash ERG, but not the wnERG, may reflect retinal nonlinearities due to the compression of energy into a short time period during a stimulus flash.

CONCLUSION

The wnERG provides a new approach to study the physiology of the retina using a stimulation method with adaptation and contrast conditions similar to natural scenes to allow for independent variation of stimulus strength and mean luminance, which is not possible with the conventional flash ERG.

TRANSLATIONAL RELEVANCE

The white noise ERG methodology will be of benefit for clinical studies and animal models in the evaluation of hypotheses related to cellular redundancy to understand the effects of disease on specific visual pathways.

Rod Electroretinograms Elicited by Silent Substitution Stimuli from the Light-Adapted Human Eye

PURPOSE

To demonstrate that silent substitution stimuli can be used to generate electroretinograms (ERGs) that effectively isolate rod photoreceptor function in humans without the need for dark adaptation, and that this approach constitutes a viable alternative to current clinical standard testing protocols.

METHODS

Rod-isolating and non-isolating sinusoidal flicker stimuli were generated on a 4 primary light-emitting diode (LED) Ganzfeld stimulator to elicit ERGs from participants with normal and compromised rod function who had not undergone dark-adaptation. Responses were subjected to Fourier analysis, and the amplitude and phase of the fundamental were used to examine temporal frequency and retinal illuminance response characteristics.

RESULTS

Electroretinograms elicited by rod-isolating silent substitution stimuli exhibit low-pass temporal frequency response characteristics with an upper response limit of 30 Hz. Responses are optimal between 5 and 8 Hz and between 10 and 100 photopic trolands (Td). There is a significant correlation between the response amplitudes obtained with the silent substitution method and current standard clinical protocols. Analysis of signal-to-noise ratios reveals significant differences between subjects with normal and compromised rod function.

CONCLUSIONS

Silent substitution provides an effective method for the isolation of human rod photoreceptor function in subjects with normal as well as compromised rod function when stimuli are used within appropriate parameter ranges.

TRANSLATIONAL RELEVANCE

This method of generating rod-mediated ERGs can be achieved without time-consuming periods of dark adaptation, provides improved isolation of rod- from cone-based activity, and will lead to the development of faster clinical electrophysiologic testing protocols with improved selectivity.

Assessment of retinal function and morphology in aging Ccl2 knockout mice

PURPOSE

The chemokine Ccl2, or monocyte chemoattractant protein-1 (MCP-1), has previously been identified as playing a potential role in many ocular diseases; however, its role in mice is less clear. We sought to correlate changes in retinal pigment epithelium (RPE) and retinal morphology with changes in function in aging Ccl2(-/-) mice.

METHODS

Ccl2(-/-) mice on a C57BL6J background were genotyped for Crb1(rd8/rd8) and were free of this mutation. Ccl2(-/-) mice and wild-type (WT) C57BL6J mice were investigated for changes in the retinal fundus and histology as a function of age. The function of the rod and cone pathways, and the rate of dark adaptation, was assessed using the electroretinogram (ERG) up to 15 months of age.

RESULTS

Fifteen-month-old Ccl2(-/-) mice had fundus lesions, more subretinal microglia/macrophages, and an increase in RPE cell size, indicative of RPE cell loss, when compared with WT mice. Within the retina, gross morphology was normal but there was an increase in Müller cell gliosis and microglial activation. These morphological changes in the Ccl2(-/-) RPE/retina did not correlate with a change in either rod or cone ERG pathway function, or with the rate of dark adaptation.

CONCLUSIONS

These data show that Ccl2 is important for preserving RPE and glial morphology with age, yet retinal function and gross morphology are maintained. Altered signaling in this chemokine pathway may, however, increase RPE and retinal vulnerability to disease.

Assessment of inner retina dysfunction and progressive ganglion cell loss in a mouse model of glaucoma

The DBA/2J mouse is a model of ocular hypertension and retinal ganglion cell (RGC) degeneration, the main features of which are iris pigment dispersion (IPD) and iris stromal atrophy (ISA). These animals also experience glaucomatous changes, including an increase in intraocular pressure (IOP) beginning at about 9-12 months of age and sectorial RGC death in the retina. The aim of this study was to determine the onset of functional changes exhibited by DBA/2J mice in the inner retina. This was performed by means of electroretinographic recordings (scotopic threshold response, STR) and their correlation with morphological changes (loss of RGCs). To this end, we recorded the scotopic threshold response in control C57BL/6J and in DBA/2J mice at different ages. The RGCs, in both DBA/2J and C57BL/6J animals, were identified at 15 months of age by retrograde tracing with an analogue of fluorogold, hydroxystilbamidine methanesulfonate (OHSt), applied on the superior colliculi. Whole mount retinas were processed to quantify the population of RGCs identified by fluorogold tracing and Brn3a immunodetection, and were counted using image analysis software; an isodensity contour plot was generated for each retina. DBA/2J mice showed a significant reduction in the positive STR (pSTR) amplitudes at 12 months of age, as compared to control C57BL/6J mice of the same age. The pSTR mean amplitude decreased to approximately 27.82% of the values recorded in control mice (p = 0.0058). STR responses decreased in both strains as a result of the natural process of aging, but the decrease was more pronounced in DBA/2J mice. Furthermore, quantification of the total number of RGCs identified by OHSt and Brn3a expression showed a reduced population of RGCs in DBA/2J mice as compared to control mice. Regression analysis revealed significant correlations between the decrease in pSTR and a non-homogeneous reduction in the number of RGCs throughout the retina. Our results indicate the existence of a correlation between retinal function impairment and RGC loss. This functional and morphological analysis allows a reliable assessment of the progression of the disease.