Mcardle Disease Associated Maculopathy and the Role of Glycogen in the Retina

Mcardle Disease Associated Maculopathy and the Role of Glycogen in the Retina

Marques JH and Beirão JM, J Ophthalmic Clin Res 2020, 7: 067 DOI: 10.24966/OCR-8887/100067 HSOA Journal of Ophthalmology & Clinical Research Case Report demanding tissues like the RPE depend on glycogen phosphoryla- McArdle Disease associated tion to produce energy and, on the other hand, glycogen erroneous accumulation may impair cellular functions. Probably due to higher Maculopathy and the Role of photoreceptor concentration and subsequent energy demand in the macula, this is the primary site for degeneration in our patient. The Glycogen in the Retina present report reinforces the role of the glycogen pathway as a pos- sible player in the pathophysiology of RPE pathologies, genetically and/or environmentally determined. Keywords: Age-related macular degeneration; Geographic atrophy; João Heitor Marques1* and João Melo Beirão1,2 Glycogen; McArdle; Retinal pigmented epithelium 1Serviço de Oftalmologia, Centro Hospitalar e Universitário do Porto, Portugal Introduction 2Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Portugal Intracellular glycogen works as a buffer for glucose metabolism. Glycogen phosphorylase breaks down glycogen, making glucose available for aerobic and anaerobic energetic pathways. It can be rapidly metabolized without ATP requirement. A deficit in glycogen phosphorylation results, not only in energy shortage, but also in its Abstract intracellular accumulation, which may further interfere with other Purpose: To report a case of maculopathy with pattern dystrophy cellular functions. and geographic atrophy in a patient with McArdle disease and to review the glycogen pathway’s disorders as a source of energy but Glycogen Storage Disease type V (GSDV), also known as McAr- also cause of disease in the retina. dle disease [1], is a genetic myopathy caused by loss-of-function mu- tation in both alleles of the PYGM gene. It results in an inherited Setting/Venue: Centro Hospitalar Universitário do Porto, Portugal. deficit of myophosphorylase, the skeletal muscle isoform of glycogen Methods: Case report with multimodal imaging, including color fun- phosphorylase enzyme. This leads, not only to ATP depletion, but also dus photography, infrared fundus photography, fluorescein angiogra- to the accumulation of ADP, inhibiting calcium pump and sodium-po- phy and optical coherence tomography. tassium pumps, during energy demand [2]. Muscle histology shows Results: A 61-year-old man with McArdle disease, a rare deficit of negative chemical staining for myophosphorylase activity and subsa- glycogen phosphorylation, with genetic and phenotypic (muscle bi- rcolemmal deposits of glycogen on periodic acid-Schiff stain [3]. opsy) confirmation. He had history of muscle weakness and pain Its estimated prevalence is 1:100000 [4], making it the most com- sincechildhood and recently complained of progressive visual loss. Fundus examination observation and multimodal imaging revealed mon disorder of skeletal muscle carbohydrate metabolism. GSDV is macular reticular pattern dystrophy of both eyes, associated with not usually a lethal condition. Clinically, it manifests as exercise intol- geographic atrophy in left eye. erance and reversible acute episodes of contractures, associated with rhabdomyolysis and myoglobinuria. Conclusion: Previous cases of McArdle disease-associated reti- nopathy with reticular pattern dystrophy had been reported. More- In the eye, the Retinal Pigmented Epithelium (RPE) is a spe- over, this is the first reported case that presented with geographic cialized tissue responsible for keeping the photoreceptors operating atrophy of the Retinal Pigmented Epithelium (RPE). Such findings and, ultimately, maintaining visual function. RPE forms the outer suggest that these phenotypes are part of the same pathological blood-retinal barrier: on one side, its tight junctions protect the retina spectrum and similar to other acquired retinal pigmented epithelium from blood-borne toxins and provides ocular immune privilege. On diseases, such as age-related macular degeneration. Metabolic high the other side, it must deliver nutrients and disposes waste products. Moreover, the RPE absorbs non-transduced light, mitigates photo-ox- *Corresponding author: João Heitor Marques, Serviço de Oftalmologia, Centro idative stress, recycles retinoids and secrets essential growth factors Hospitalar Universitário do Porto, Hospital Santo António (HSA), Largo do Prof. [5,6]. Abel Salazar, 4099-001 Porto, Portugal, Tel: +351 913680726: E-mail: joao- heitormarques@gmail.com Glucose is the major energy substrate for retinal metabolism [7] Citation: Marques JH, Beirão JM (2020) McArdle Disease associated Macu- and its source to the outer retina is the RPE. The RPE also manages lopathy and the Role of Glycogen in the Retina. J Ophthalmic Clin Res 7: 067. the conversion of glucose to glycogen and back, as a buffer [8], be- Received: April 06, 2020; Accepted: April 13, 2020; Published: April 20, 2020 tween the choriocapillaris and the photoreceptors. This way, it is able to manage the demand of the photoreceptors. Copyright: © 2020 Marques JH, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits un- The RPE is implicated in the pathogenesis of several retinal de- restricted use, distribution, and reproduction in any medium, provided the original generations, including Age-Related Macular Degeneration (AMD) author and source are credited. [9]. Citation: Marques JH, Beirão JM (2020) McArdle Disease associated Maculopathy and the Role of Glycogen in the Retina. J Ophthalmic Clin Res 7: 067. • Page 2 of 5 • Therefore, our purpose is to report a case of GSDV associated with geographic atrophy of the RPE and to review the glycogen path- ways’ as a source of energy but also degeneration in the retina. Methods 1. Case report with macular multimodal imaging, including color fundus photography, infrared fundus photography, fluorescein angiography and spectral-domain optical coherence tomography. 2. Systematic review of indexed articles on the glycogen role in Age-Related Macular Degeneration that were published until Feb- ruary 2020. Results We report a case of a man with exercise intolerance and pain during physical efforts since a young age. He had no relevant medi- cal history except for controlled arterial hypertension and past history of smoking (he quit 15 years before). At the age of 61, on routine blood samples, repeated over-the-limit creatine kinase measurements motivated the referral to our center. GSDV diagnosis was made with suggestive muscle biopsy and genetic confirmation (compound het- erozygote PYGM gene with mutations C148T and T2392CA, both associated with loss of function of myophosphorylase). Figure 1: Infra-red fundus photograph (left) and corresponding OCT B-scan (right) of the right (upper) and left (bottom) eyes. Six months after diagnosis, the patient complained of progressive vision loss in both eyes. Given this, he was referred to our Ophthal- mology Department. His visual acuity was 0.7 on his right eye and 0.4 on his left eye (decimal scale). Intraocular pressure measured with Goldmann applanation tonometer was 16mmHg in both eyes. Ante- rior segment examination was unremarkable. Fundus observation re- vealed no typical drusen in the periphery or posterior pole. There was macular reticular-like pattern dystrophy in both eyes, associated with geographic atrophy in left eye. Color and infra-red fundus photography, fluorescein angiography (Figure 1) and spectral-domain macular optical coherence tomogra- phy (Figure 2) confirmed the findings: On the right eye, optical co- herence tomography shown no sub-RPE deposits (drusen) and focal degeneration of RPE and external photoreceptor tips together with corresponding changes in the external nuclear layer. On the left eye, optical coherence tomography revealed no sub-RPE deposits (dru- sen), an area of complete atrophy of the RPE and external retinal lay- ers and changes similar to the previous described around the atrophic area. Discussion The present case-report confirms that degenerative geographic Figure 2: Fluorescein angiography at minute 2 (upper) and color fundus photo- atrophy is not a specific finding of classic AMD and is not always graph (bottom) of right and left eyes. accompanied by the presence of drusen. Moreover, pattern dystrophy and geographic atrophy may be part of the same pathological spec- trum. Regarding our case, we had no ophthalmic records before the di- Although there is no direct causal relationship between GSDV and agnosis, but visual symptoms started just in the seventh decade of the development of RPE atrophy, this case suggests that a single defi- life. Thus, we may assume that macular RPE atrophy began at around cit in energetic pathways may be capable of causing RPE atrophy or, that time, even if other asymptomatic retinal changes were eventual- at least, accelerate it. ly present before. Given that the metabolic deficit is congenital, an additional factor should be involved to explain the late onset of the In another perspective, it favors the hypothesis that the current disease. If we consider age as the second factor, we may postulate that definition of AMD encompasses not a single disease, since different glycogen phosphorylation deficit leads to a slow RPE suffering and pathological paths may lead to the same manifestation. debris accumulation that, after decades, results in cellular death. Volume 7 • Issue 1 • 100067 J Ophthalmic Clin Res ISSN:

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