Differential binding to glycotopes among the layers of three mammalian retinal neurons by man-containing N-linked glycan, T(alpha) (Galbeta1-3GalNAcalpha1-), Tn (GalNAcalpha1-Ser/Thr) and I (beta)/II (beta) (Galbeta1-3/4GlcNAcbeta-) reactive lectins

Case Report: Multiple Retinal Astrocytic Hamartomas in Congenital Disorder of Glycosylation-Ia

Congenital disorder of glycosylation-Ia (CDG-Ia) is a rare autosomal recessive genetic disorder, characterized by systemic and ophthalmological abnormalities. Here, we report multiple retinal astrocytic hamartomas as a new retinal finding in an adolescent affected by congenital disorder of CDG-Ia. A 15-year-old boy affected by CDG-Ia underwent full ophthalmic examination, full field electroretinography (ERG) evaluation and retinal multimodal imaging, including: fundus photography, spectral domain optical coherence tomography (SD-OCT) and blue fundus autofluorescence (FAF). Blue FAF showed multiple papillary and iuxtapapillary bilateral hyper-FAF lesions, corresponding to hyperreflective thickening of the retinal nerve fiber layer, with internal optical empty spaces and posterior dense optical shadowing at SD-OCT. These imaging findings were consistent with retinal astrocytic hamartomas. Scotopic ERG response was significantly reduced in both eyes. Macular edema and absence of the retinal outer segments layer were also detectable. Retinal multi-modal imaging provides additional insights about retinal involvement of patients affected by CDG-Ia. In particular, this case shows the presence of multiple retinal astrocytic hamartomas.

Network analysis of adhesion/growth-regulatory galectins and their binding sites in adult chicken retina and choroid

The highly ordered multilayered organization of the adult chicken retina is a suitable test model for examining zonal distribution of the members of a bioeffector family. Based on the concept of the sugar code, the functional pairing of glycan epitopes with cognate receptors (lectins) is emerging as a means to explain the control of diverse physiological activities. Having recently completed the biochemical characterization of all seven adhesion/growth-regulatory galectins present in chicken, it was possible to establish how the individual characteristics of their expression profiles add up to shape the galectin network, which until now has not been defined at this level of complexity. This information will also have relevance in explaining the region-specific presence of glycan determinants in the retina, as illustrated in the first part of this study using a panel of nine plant/fungal agglutinins. The following systematic monitoring of the galectins yielded patterns for which quantitative and qualitative differences were detected. Obviously, positivity in distinct layers is not confined to a single protein of this family, e.g. CG-1A, CG-3 or CG-8. These results underline the requirement for network analysis for these proteins that can functionally interact in additive or antagonistic modes. Labeling of the tissue galectins facilitated profiling of their accessible binding sites. It also revealed differences among the galectin family members, highlighting the ability of this method to define binding properties on the level of tissue sections. Methodologically, the detection of endogenous lectins intimates that cognate glycans can become inaccessible, a notable caveat for lectin histochemical studies.

Retinal characteristics of the congenital disorder of glycosylation PMM2-CDG

The congenital disorder of glycosylation, PMM2-CDG, is associated with progressive photoreceptor degeneration, which causes a pigmentary retinopathy. We identified a sibling pair, mildly affected with PMM2-CDG, who showed preserved photoreceptor function, but profound deficits of the 'on-pathway' in the retina. This localises the site of early, or initial, retinal dysfunction in PMM2-CDG to the synapse in the outer plexiform layer between bipolar cells, photoreceptors and horizontal cells. We sought wider evidence to support this novel finding by reviewing retrospectively the case notes of eight patients, diagnosed with PMM2-CDG between the ages of 7 months to 16 years. We compared the clinical presentation and electroretinograms, (ERGs), of these patients with the sibling pair. We found that five of eight patients showed characteristic ERG features of on-pathway dysfunction in the form of reduced ERG b-wave amplitude. The remaining three patients had significant photoreceptor dysfunction by the time of ERG recording, and both a- and b-wave amplitudes were markedly attenuated. We conclude that ERG signs of on-pathway dysfunction can be detected in the early stages of PMM2-CDG. Referral for electroretinography evidence of this specific on-pathway deficit, with preservation of oscillatory potentials, can help establish the diagnosis of infants with developmental delay or failure to thrive in whom a glycosylation defect is suspected. Also by increasing our understanding of the interaction of N-glycoproteins at this synapse we may be able to design future therapeutic intervention to prevent or ameliorate the progressive visual loss associated with PMM2-CDG.