Abstract
Purpose:
To identify the relationship between the Myotonic Dystrophy type 1 (MD1) and some subtypes of other retinal dystrophies from based on electrophysiological findings. To describe a possible causal link between retinal manifestations of DM1 and known molecular mechanisms as well as parental origin of genetic transmission.
Methods:
An observational, descriptive study of 29 cases with MD1 in the neuro-ophthalmology department of the Cuban Institute of Neurology and Neurosurgery was conducted from March 2013 to March 2014. Ophthalmological examination, electroretinograms (ERG) and electro-oculograms (EOG) were performed complying ISCEV protocol. Maternal/paternal transmission routes were taken into account. Univariate and multivariate statistical analysis were performed, and odds ratios (OR) were calculated.
Results:
Mesopic ERG was decreased in 75.9% [average a wave amplitude: 221.98 (± 6.393) and average b wave: 300.10 (± 11,343)]. EOG was also decreased in 39.7% [mean Arden coefficient: 2.03 (± 0.76)]. Maternal transmission of MD1 increased 2.4 times the probability to have an affected ERG (OR = 2.403; 95% CI 1.611 to 3.584). A significant association was found (X2=12,504; gl=1; p=0,000) between decreased ERG amplitudes and maternal transmission of the disease.
Conclusions:
Photoreceptor dysfunction was greater than RPE dysfunction in opposed to what is classically described in DM1. These findings may contribute to future retinal dystrophy classifications. The DMPK (19q13,33) gene is very close to CRX (19q13,32), and large triplet expansions may affect the later one. These CTG expansions are frequently observed in maternal transmission of DM1 and could explain the electrophysiological phenotypic variability in these patients.