Identification of ocular associations with systemic diseases can aid diagnosis and phenotyping and can yield pathophysiologic insights.

McArdle disease (glycogen storage disease type V) is a rare metabolic myopathy (estimated prevalence, 1/100 000) resulting from biallelic mutations in the PYGM gene, encoding muscle glycogen phosphorylase (reviewed by Lucia et al1), comments a study.

It was carried out by Omar A. Mahroo, PhD, Kamron N. Khan, PhD, FRCOphth, Genevieve Wright, MSc, Zoe Ockrim, FRCOphth, Renata S. Scalco, MD, Anthony G. Robson, PhD, Adnan Tufail, MD(Res), FRCOphth, Michel Michaelides, MD(Res), FRCOphth, Ros Quinlivan, MD, FRCP, Andrew R. Webster, MD(Res), FRCOphth.

The article was published in Ophthalmology journal.

Patients experience exercise intolerance and risk acute rhabdomyolysis, although life expectancy is rarely affected. A case report from 1988 described pattern dystrophy of the retinal pigment epithelium (RPE) in an affected patient.2 Two further cases have been reported.3, 4 With only 3 cases, chance association is possible; the 2 entities may be unrelated.
Pattern dystrophies can be associated with mutations in a number of genes, most frequently PRPH2.

Results of the study

The study reports multimodal imaging findings of a distinctive retinopathy in 4 unrelated patients with McArdle disease, similar to the previous case reports. The research team also reports results of retinal electrophysiologic analysis: despite far peripheral abnormalities on ultrawide-field imaging, there was no definite electrophysiologic evidence of generalized retinal, or generalized RPE, dysfunction (full-field electroretinography and electro-oculography light rise results were normal).

Screening results for mutations in a number of macular dystrophy genes were negative. In particular, the findings could not be attributed to mutations in PRPH2, which would have been most likely to result in a similar retinal phenotype.

The results of this study are of clinical significance because they support the association of this retinopathy with McArdle disease and can reduce the likelihood of misdiagnosis; this is increasingly important because particular genetic causes of retinopathy (including ABCA4) are subject to a number of novel treatment trials.

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